<?xml version="1.0" encoding="US-ASCII" standalone="no"?>
    <!-- Field: Doc-Info; Name: Generator; Value: GoFiler Complete; Version: 6.3a -->
    <!-- Field: Doc-Info; Name: VendorURI; Value: https://www.novaworks.com -->
    <!-- Field: Doc-Info; Name: Status; Value: 0x00000000 -->
<link:linkbase xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:xbrldt="http://xbrl.org/2005/xbrldt" xmlns:xbrli="http://www.xbrl.org/2003/instance" xsi:schemaLocation="http://www.xbrl.org/2003/linkbase http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd">
    <link:roleRef xlink:type="simple" xlink:href="hrow-20250930.xsd#Cover" roleURI="http://harrow.com/role/Cover" />
    <link:roleRef xlink:type="simple" xlink:href="hrow-20250930.xsd#BalanceSheets" roleURI="http://harrow.com/role/BalanceSheets" />
    <link:roleRef xlink:type="simple" xlink:href="hrow-20250930.xsd#BalanceSheetsParenthetical" roleURI="http://harrow.com/role/BalanceSheetsParenthetical" />
    <link:roleRef xlink:type="simple" xlink:href="hrow-20250930.xsd#StatementsOfOperations" roleURI="http://harrow.com/role/StatementsOfOperations" />
    <link:roleRef xlink:type="simple" xlink:href="hrow-20250930.xsd#StatementsOfStockholdersEquity" roleURI="http://harrow.com/role/StatementsOfStockholdersEquity" />
    <link:roleRef xlink:type="simple" xlink:href="hrow-20250930.xsd#StatementsOfCashFlows" roleURI="http://harrow.com/role/StatementsOfCashFlows" />
    <link:roleRef xlink:type="simple" xlink:href="hrow-20250930.xsd#DescriptionOfBusinessAndBasisOfPresentation" roleURI="http://harrow.com/role/DescriptionOfBusinessAndBasisOfPresentation" />
    <link:roleRef xlink:type="simple" xlink:href="hrow-20250930.xsd#SummaryOfSignificantAccountingPolicies" roleURI="http://harrow.com/role/SummaryOfSignificantAccountingPolicies" />
    <link:roleRef xlink:type="simple" xlink:href="hrow-20250930.xsd#Revenues" roleURI="http://harrow.com/role/Revenues" />
    <link:roleRef xlink:type="simple" xlink:href="hrow-20250930.xsd#Inventories" roleURI="http://harrow.com/role/Inventories" />
    <link:roleRef xlink:type="simple" xlink:href="hrow-20250930.xsd#PrepaidExpensesAndOtherCurrentAssets" roleURI="http://harrow.com/role/PrepaidExpensesAndOtherCurrentAssets" />
    <link:roleRef xlink:type="simple" xlink:href="hrow-20250930.xsd#PropertyPlantAndEquipment" roleURI="http://harrow.com/role/PropertyPlantAndEquipment" />
    <link:roleRef xlink:type="simple" xlink:href="hrow-20250930.xsd#CapitalizedSoftwareCosts" roleURI="http://harrow.com/role/CapitalizedSoftwareCosts" />
    <link:roleRef xlink:type="simple" xlink:href="hrow-20250930.xsd#IntangibleAssetsAndGoodwill" roleURI="http://harrow.com/role/IntangibleAssetsAndGoodwill" />
    <link:roleRef xlink:type="simple" xlink:href="hrow-20250930.xsd#AccountsPayableAndAccruedExpenses" roleURI="http://harrow.com/role/AccountsPayableAndAccruedExpenses" />
    <link:roleRef xlink:type="simple" xlink:href="hrow-20250930.xsd#Debt" roleURI="http://harrow.com/role/Debt" />
    <link:roleRef xlink:type="simple" xlink:href="hrow-20250930.xsd#Leases" roleURI="http://harrow.com/role/Leases" />
    <link:roleRef xlink:type="simple" xlink:href="hrow-20250930.xsd#StockholdersEquityAndStock-basedCompensation" roleURI="http://harrow.com/role/StockholdersEquityAndStock-basedCompensation" />
    <link:roleRef xlink:type="simple" xlink:href="hrow-20250930.xsd#CommitmentsAndContingencies" roleURI="http://harrow.com/role/CommitmentsAndContingencies" />
    <link:roleRef xlink:type="simple" xlink:href="hrow-20250930.xsd#SegmentsAndConcentrations" roleURI="http://harrow.com/role/SegmentsAndConcentrations" />
    <link:roleRef xlink:type="simple" xlink:href="hrow-20250930.xsd#SubsequentEvents" roleURI="http://harrow.com/role/SubsequentEvents" />
    <link:roleRef xlink:type="simple" xlink:href="hrow-20250930.xsd#SummaryOfSignificantAccountingPoliciesPolicies" roleURI="http://harrow.com/role/SummaryOfSignificantAccountingPoliciesPolicies" />
    <link:roleRef xlink:type="simple" xlink:href="hrow-20250930.xsd#SummaryOfSignificantAccountingPoliciesTables" roleURI="http://harrow.com/role/SummaryOfSignificantAccountingPoliciesTables" />
    <link:roleRef xlink:type="simple" xlink:href="hrow-20250930.xsd#RevenuesTables" roleURI="http://harrow.com/role/RevenuesTables" />
    <link:roleRef xlink:type="simple" xlink:href="hrow-20250930.xsd#InventoriesTables" roleURI="http://harrow.com/role/InventoriesTables" />
    <link:roleRef xlink:type="simple" xlink:href="hrow-20250930.xsd#PrepaidExpensesAndOtherCurrentAssetsTables" roleURI="http://harrow.com/role/PrepaidExpensesAndOtherCurrentAssetsTables" />
    <link:roleRef xlink:type="simple" xlink:href="hrow-20250930.xsd#PropertyPlantAndEquipmentTables" roleURI="http://harrow.com/role/PropertyPlantAndEquipmentTables" />
    <link:roleRef xlink:type="simple" xlink:href="hrow-20250930.xsd#CapitalizedSoftwareCostsTables" roleURI="http://harrow.com/role/CapitalizedSoftwareCostsTables" />
    <link:roleRef xlink:type="simple" xlink:href="hrow-20250930.xsd#IntangibleAssetsAndGoodwillTables" roleURI="http://harrow.com/role/IntangibleAssetsAndGoodwillTables" />
    <link:roleRef xlink:type="simple" xlink:href="hrow-20250930.xsd#AccountsPayableAndAccruedExpensesTables" roleURI="http://harrow.com/role/AccountsPayableAndAccruedExpensesTables" />
    <link:roleRef xlink:type="simple" xlink:href="hrow-20250930.xsd#DebtTables" roleURI="http://harrow.com/role/DebtTables" />
    <link:roleRef xlink:type="simple" xlink:href="hrow-20250930.xsd#LeasesTables" roleURI="http://harrow.com/role/LeasesTables" />
    <link:roleRef xlink:type="simple" xlink:href="hrow-20250930.xsd#StockholdersEquityAndStock-basedCompensationTables" roleURI="http://harrow.com/role/StockholdersEquityAndStock-basedCompensationTables" />
    <link:roleRef xlink:type="simple" xlink:href="hrow-20250930.xsd#SegmentsAndConcentrationsTables" roleURI="http://harrow.com/role/SegmentsAndConcentrationsTables" />
    <link:roleRef xlink:type="simple" xlink:href="hrow-20250930.xsd#ScheduleOfAccountsReceivableAllowanceOfCreditLossDetails" roleURI="http://harrow.com/role/ScheduleOfAccountsReceivableAllowanceOfCreditLossDetails" />
    <link:roleRef xlink:type="simple" xlink:href="hrow-20250930.xsd#ScheduleOfEstimatedFairValueDetails" roleURI="http://harrow.com/role/ScheduleOfEstimatedFairValueDetails" />
    <link:roleRef xlink:type="simple" xlink:href="hrow-20250930.xsd#DescriptionOfBusinessAndBasisOfPresentationDetailsNarrative" roleURI="http://harrow.com/role/DescriptionOfBusinessAndBasisOfPresentationDetailsNarrative" />
    <link:roleRef xlink:type="simple" xlink:href="hrow-20250930.xsd#ScheduleOfBasicEarningsPerCommonShareDetails" roleURI="http://harrow.com/role/ScheduleOfBasicEarningsPerCommonShareDetails" />
    <link:roleRef xlink:type="simple" xlink:href="hrow-20250930.xsd#ScheduleOfDilutedNetIncomePerShareDetails" roleURI="http://harrow.com/role/ScheduleOfDilutedNetIncomePerShareDetails" />
    <link:roleRef xlink:type="simple" xlink:href="hrow-20250930.xsd#ScheduleOfBasicAndDilutedEarningsPerCommonShareDetails" roleURI="http://harrow.com/role/ScheduleOfBasicAndDilutedEarningsPerCommonShareDetails" />
    <link:roleRef xlink:type="simple" xlink:href="hrow-20250930.xsd#SummaryOfSignificantAccountingPoliciesDetailsNarrative" roleURI="http://harrow.com/role/SummaryOfSignificantAccountingPoliciesDetailsNarrative" />
    <link:roleRef xlink:type="simple" xlink:href="hrow-20250930.xsd#ScheduleOfAccrualsAndAllowancesDetails" roleURI="http://harrow.com/role/ScheduleOfAccrualsAndAllowancesDetails" />
    <link:roleRef xlink:type="simple" xlink:href="hrow-20250930.xsd#ScheduleOfDisaggregatedRevenueDetails" roleURI="http://harrow.com/role/ScheduleOfDisaggregatedRevenueDetails" />
    <link:roleRef xlink:type="simple" xlink:href="hrow-20250930.xsd#RevenuesDetailsNarrative" roleURI="http://harrow.com/role/RevenuesDetailsNarrative" />
    <link:roleRef xlink:type="simple" xlink:href="hrow-20250930.xsd#ScheduleOfInventoriesDetails" roleURI="http://harrow.com/role/ScheduleOfInventoriesDetails" />
    <link:roleRef xlink:type="simple" xlink:href="hrow-20250930.xsd#ScheduleOfPrepaidExpensesAndOtherCurrentAssetsDetails" roleURI="http://harrow.com/role/ScheduleOfPrepaidExpensesAndOtherCurrentAssetsDetails" />
    <link:roleRef xlink:type="simple" xlink:href="hrow-20250930.xsd#ScheduleOfPropertyPlantAndEquipmentDetails" roleURI="http://harrow.com/role/ScheduleOfPropertyPlantAndEquipmentDetails" />
    <link:roleRef xlink:type="simple" xlink:href="hrow-20250930.xsd#PropertyPlantAndEquipmentDetailsNarrative" roleURI="http://harrow.com/role/PropertyPlantAndEquipmentDetailsNarrative" />
    <link:roleRef xlink:type="simple" xlink:href="hrow-20250930.xsd#ScheduleOfCapitalizedSoftwareCostsDetails" roleURI="http://harrow.com/role/ScheduleOfCapitalizedSoftwareCostsDetails" />
    <link:roleRef xlink:type="simple" xlink:href="hrow-20250930.xsd#CapitalizedSoftwareCostsDetailsNarrative" roleURI="http://harrow.com/role/CapitalizedSoftwareCostsDetailsNarrative" />
    <link:roleRef xlink:type="simple" xlink:href="hrow-20250930.xsd#ScheduleOfIntangibleAssetsDetails" roleURI="http://harrow.com/role/ScheduleOfIntangibleAssetsDetails" />
    <link:roleRef xlink:type="simple" xlink:href="hrow-20250930.xsd#ScheduleOfAmortizationExpensesForIntangibleAssetsDetails" roleURI="http://harrow.com/role/ScheduleOfAmortizationExpensesForIntangibleAssetsDetails" />
    <link:roleRef xlink:type="simple" xlink:href="hrow-20250930.xsd#ScheduleOfEstimatedFutureAmortizationExpenseDetails" roleURI="http://harrow.com/role/ScheduleOfEstimatedFutureAmortizationExpenseDetails" />
    <link:roleRef xlink:type="simple" xlink:href="hrow-20250930.xsd#IntangibleAssetsAndGoodwillDetailsNarrative" roleURI="http://harrow.com/role/IntangibleAssetsAndGoodwillDetailsNarrative" />
    <link:roleRef xlink:type="simple" xlink:href="hrow-20250930.xsd#ScheduleOfAccountsPayableAndAccruedExpensesDetails" roleURI="http://harrow.com/role/ScheduleOfAccountsPayableAndAccruedExpensesDetails" />
    <link:roleRef xlink:type="simple" xlink:href="hrow-20250930.xsd#ScheduleOfLongTermDebtDetails" roleURI="http://harrow.com/role/ScheduleOfLongTermDebtDetails" />
    <link:roleRef xlink:type="simple" xlink:href="hrow-20250930.xsd#ScheduleOfLongTermDebtDetailsParenthetical" roleURI="http://harrow.com/role/ScheduleOfLongTermDebtDetailsParenthetical" />
    <link:roleRef xlink:type="simple" xlink:href="hrow-20250930.xsd#ScheduleOfFutureMinimumPaymentUnderNotesPayablesDetails" roleURI="http://harrow.com/role/ScheduleOfFutureMinimumPaymentUnderNotesPayablesDetails" />
    <link:roleRef xlink:type="simple" xlink:href="hrow-20250930.xsd#DebtDetailsNarrative" roleURI="http://harrow.com/role/DebtDetailsNarrative" />
    <link:roleRef xlink:type="simple" xlink:href="hrow-20250930.xsd#LeasesDetailsNarrative" roleURI="http://harrow.com/role/LeasesDetailsNarrative" />
    <link:roleRef xlink:type="simple" xlink:href="hrow-20250930.xsd#ScheduleOfFutureLeasePaymentsUnderOperatingLeasesDetails" roleURI="http://harrow.com/role/ScheduleOfFutureLeasePaymentsUnderOperatingLeasesDetails" />
    <link:roleRef xlink:type="simple" xlink:href="hrow-20250930.xsd#ScheduleOfStockOptionPlanActivityDetails" roleURI="http://harrow.com/role/ScheduleOfStockOptionPlanActivityDetails" />
    <link:roleRef xlink:type="simple" xlink:href="hrow-20250930.xsd#ScheduleOfFairValueAssumptionsDetails" roleURI="http://harrow.com/role/ScheduleOfFairValueAssumptionsDetails" />
    <link:roleRef xlink:type="simple" xlink:href="hrow-20250930.xsd#ScheduleOfStockOptionOutstandingAndExercisableDetails" roleURI="http://harrow.com/role/ScheduleOfStockOptionOutstandingAndExercisableDetails" />
    <link:roleRef xlink:type="simple" xlink:href="hrow-20250930.xsd#ScheduleOfRestrictedStockUnitsActivityDetails" roleURI="http://harrow.com/role/ScheduleOfRestrictedStockUnitsActivityDetails" />
    <link:roleRef xlink:type="simple" xlink:href="hrow-20250930.xsd#ScheduleOfPerformanceStockUnitsDetails" roleURI="http://harrow.com/role/ScheduleOfPerformanceStockUnitsDetails" />
    <link:roleRef xlink:type="simple" xlink:href="hrow-20250930.xsd#ScheduleOfPerformanceStockUnitsActivityDetails" roleURI="http://harrow.com/role/ScheduleOfPerformanceStockUnitsActivityDetails" />
    <link:roleRef xlink:type="simple" xlink:href="hrow-20250930.xsd#ScheduleOfStockBasedCompensationGrantedToEmployeesDirectorsAndConsultantsDetails" roleURI="http://harrow.com/role/ScheduleOfStockBasedCompensationGrantedToEmployeesDirectorsAndConsultantsDetails" />
    <link:roleRef xlink:type="simple" xlink:href="hrow-20250930.xsd#StockholdersEquityAndStock-basedCompensationDetailsNarrative" roleURI="http://harrow.com/role/StockholdersEquityAndStock-basedCompensationDetailsNarrative" />
    <link:roleRef xlink:type="simple" xlink:href="hrow-20250930.xsd#CommitmentsAndContingenciesDetailsNarrative" roleURI="http://harrow.com/role/CommitmentsAndContingenciesDetailsNarrative" />
    <link:roleRef xlink:type="simple" xlink:href="hrow-20250930.xsd#ScheduleOfSegmentNetRevenuesDetails" roleURI="http://harrow.com/role/ScheduleOfSegmentNetRevenuesDetails" />
    <link:roleRef xlink:type="simple" xlink:href="hrow-20250930.xsd#ScheduleOfRevenuesBySegmentDetails" roleURI="http://harrow.com/role/ScheduleOfRevenuesBySegmentDetails" />
    <link:roleRef xlink:type="simple" xlink:href="hrow-20250930.xsd#SegmentsAndConcentrationsDetailsNarrative" roleURI="http://harrow.com/role/SegmentsAndConcentrationsDetailsNarrative" />
    <link:roleRef xlink:type="simple" xlink:href="hrow-20250930.xsd#SubsequentEventsDetailsNarrative" roleURI="http://harrow.com/role/SubsequentEventsDetailsNarrative" />
    <link:roleRef xlink:type="simple" xlink:href="https://xbrl.sec.gov/ecd/2025/ecd-2025.xsd#PvpDisclosureWithAdditionalMeasures" roleURI="http://xbrl.sec.gov/ecd/role/PvpDisclosureWithAdditionalMeasures" />
    <link:roleRef xlink:type="simple" xlink:href="https://xbrl.sec.gov/ecd/2025/ecd-2025.xsd#PvpTable" roleURI="http://xbrl.sec.gov/ecd/role/PvpTable" />
    <link:roleRef xlink:type="simple" xlink:href="https://xbrl.sec.gov/ecd/2025/ecd-2025.xsd#PvpAdjustmentsToCompensation" roleURI="http://xbrl.sec.gov/ecd/role/PvpAdjustmentsToCompensation" />
    <link:roleRef xlink:type="simple" xlink:href="https://xbrl.sec.gov/ecd/2025/ecd-2025.xsd#TabularListsByExecutiveCategory" roleURI="http://xbrl.sec.gov/ecd/role/TabularListsByExecutiveCategory" />
    <link:roleRef xlink:type="simple" xlink:href="https://xbrl.sec.gov/ecd/2025/ecd-2025.xsd#TabularListMeasures" roleURI="http://xbrl.sec.gov/ecd/role/TabularListMeasures" />
    <link:roleRef xlink:type="simple" xlink:href="https://xbrl.sec.gov/ecd/2025/ecd-2025.xsd#PvpMeasures" roleURI="http://xbrl.sec.gov/ecd/role/PvpMeasures" />
    <link:roleRef xlink:type="simple" xlink:href="https://xbrl.sec.gov/ecd/2025/ecd-2025.xsd#PvpExecutiveCategoriesOnly" roleURI="http://xbrl.sec.gov/ecd/role/PvpExecutiveCategoriesOnly" />
    <link:roleRef xlink:type="simple" xlink:href="https://xbrl.sec.gov/ecd/2025/ecd-2025.xsd#PvpAdjustmentsOnly" roleURI="http://xbrl.sec.gov/ecd/role/PvpAdjustmentsOnly" />
    <link:roleRef xlink:type="simple" xlink:href="https://xbrl.sec.gov/ecd/2025/ecd-2025.xsd#IndividualsOnly" roleURI="http://xbrl.sec.gov/ecd/role/IndividualsOnly" />
    <link:roleRef xlink:type="simple" xlink:href="https://xbrl.sec.gov/ecd/2025/ecd-2025.xsd#AwardTypeOnly" roleURI="http://xbrl.sec.gov/ecd/AwardTypeOnly" />
    <link:roleRef xlink:type="simple" xlink:href="https://xbrl.sec.gov/ecd/2025/ecd-2025.xsd#TradingArrangmentsOnly" roleURI="http://xbrl.sec.gov/ecd/role/TradingArrangementsOnly" />
    <link:roleRef xlink:type="simple" xlink:href="https://xbrl.sec.gov/ecd/2025/ecd-2025.xsd#ForgoneRecoveries" roleURI="http://xbrl.sec.gov/ecd/role/ForgoneRecoveries" />
    <link:roleRef xlink:type="simple" xlink:href="https://xbrl.sec.gov/ecd/2025/ecd-2025.xsd#OutstandingRecoveries" roleURI="http://xbrl.sec.gov/ecd/role/OutstandingRecoveries" />
    <link:roleRef xlink:type="simple" xlink:href="https://xbrl.sec.gov/ecd/2025/ecd-2025.xsd#AwardsCloseToMnpiDisc" roleURI="http://xbrl.sec.gov/ecd/role/AwardsCloseToMnpiDisc" />
    <link:roleRef xlink:type="simple" xlink:href="https://xbrl.sec.gov/ecd/2025/ecd-2025.xsd#InsiderTradingArrangemenstByInd" roleURI="http://xbrl.sec.gov/ecd/role/InsiderTradingArrangementsByInd" />
    <link:roleRef xlink:type="simple" xlink:href="https://xbrl.sec.gov/ecd/2025/ecd-2025.xsd#Defaults" roleURI="http://xbrl.sec.gov/ecd/role/Defaults" />
    <link:arcroleRef xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#hypercube-dimension" arcroleURI="http://xbrl.org/int/dim/arcrole/hypercube-dimension" />
    <link:arcroleRef xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-domain" arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-domain" />
    <link:arcroleRef xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#domain-member" arcroleURI="http://xbrl.org/int/dim/arcrole/domain-member" />
    <link:arcroleRef xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#all" arcroleURI="http://xbrl.org/int/dim/arcrole/all" />
    <link:arcroleRef xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#notAll" arcroleURI="http://xbrl.org/int/dim/arcrole/notAll" />
    <link:arcroleRef xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-default" arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-default" />
    <link:definitionLink xlink:type="extended" xlink:role="http://harrow.com/role/Cover" xlink:title="00000001 - Document - Cover" />
    <link:definitionLink xlink:type="extended" xlink:role="http://harrow.com/role/BalanceSheets" xlink:title="00000002 - Statement - Condensed Consolidated Balance Sheets" />
    <link:definitionLink xlink:type="extended" xlink:role="http://harrow.com/role/BalanceSheetsParenthetical" xlink:title="00000003 - Statement - Condensed Consolidated Balance Sheets (Parenthetical)" />
    <link:definitionLink xlink:type="extended" xlink:role="http://harrow.com/role/StatementsOfOperations" xlink:title="00000004 - Statement - Condensed Consolidated Statements of Operations (Unaudited)">
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaapStatementLineItems" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaapStatementTable" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xbrldt:contextElement="segment" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapStatementTable" xlink:type="arc" order="10" xbrldt:closed="true" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ProductOrServiceAxis" xlink:label="loc_srtProductOrServiceAxis" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaapStatementTable" xlink:to="loc_srtProductOrServiceAxis" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ProductsAndServicesDomain" xlink:label="loc_srtProductsAndServicesDomain" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srtProductOrServiceAxis" xlink:to="loc_srtProductsAndServicesDomain" xlink:type="arc" order="20" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ProductsAndServicesDomain" xlink:label="loc_srtProductsAndServicesDomain_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xbrldt:contextElement="segment" xlink:from="loc_srtProductOrServiceAxis" xlink:to="loc_srtProductsAndServicesDomain_10" xlink:type="arc" order="30" />
      <link:loc xlink:type="locator" xlink:href="hrow-20250930.xsd#HROW_ProductSalesNetMember" xlink:label="loc_HROWProductSalesNetMember_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srtProductsAndServicesDomain" xlink:to="loc_HROWProductSalesNetMember_40" xlink:type="arc" order="41" />
      <link:loc xlink:type="locator" xlink:href="hrow-20250930.xsd#HROW_OtherRevenuesMember" xlink:label="loc_HROWOtherRevenuesMember_80" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srtProductsAndServicesDomain" xlink:to="loc_HROWOtherRevenuesMember_80" xlink:type="arc" order="81" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevenuesAbstract" xlink:label="loc_us-gaapRevenuesAbstract_130" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapRevenuesAbstract_130" xlink:type="arc" order="0" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax" xlink:label="loc_us-gaapRevenueFromContractWithCustomerExcludingAssessedTax_130" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapRevenuesAbstract_130" xlink:to="loc_us-gaapRevenueFromContractWithCustomerExcludingAssessedTax_130" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CostOfGoodsAndServicesSold" xlink:label="loc_us-gaapCostOfGoodsAndServicesSold_130" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapCostOfGoodsAndServicesSold_130" xlink:type="arc" order="2" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_GrossProfit" xlink:label="loc_us-gaapGrossProfit_130" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapGrossProfit_130" xlink:type="arc" order="3" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OperatingExpensesAbstract" xlink:label="loc_us-gaapOperatingExpensesAbstract_130" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapOperatingExpensesAbstract_130" xlink:type="arc" order="4" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SellingGeneralAndAdministrativeExpense" xlink:label="loc_us-gaapSellingGeneralAndAdministrativeExpense_130" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapOperatingExpensesAbstract_130" xlink:to="loc_us-gaapSellingGeneralAndAdministrativeExpense_130" xlink:type="arc" order="5" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ResearchAndDevelopmentExpense" xlink:label="loc_us-gaapResearchAndDevelopmentExpense_130" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapOperatingExpensesAbstract_130" xlink:to="loc_us-gaapResearchAndDevelopmentExpense_130" xlink:type="arc" order="6" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OperatingExpenses" xlink:label="loc_us-gaapOperatingExpenses_130" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapOperatingExpensesAbstract_130" xlink:to="loc_us-gaapOperatingExpenses_130" xlink:type="arc" order="7" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OperatingIncomeLoss" xlink:label="loc_us-gaapOperatingIncomeLoss_130" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapOperatingIncomeLoss_130" xlink:type="arc" order="8" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NonoperatingIncomeExpenseAbstract" xlink:label="loc_us-gaapNonoperatingIncomeExpenseAbstract_130" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapNonoperatingIncomeExpenseAbstract_130" xlink:type="arc" order="9" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InterestExpenseNonoperating" xlink:label="loc_us-gaapInterestExpenseNonoperating_130" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapNonoperatingIncomeExpenseAbstract_130" xlink:to="loc_us-gaapInterestExpenseNonoperating_130" xlink:type="arc" order="10" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_GainLossOnInvestments" xlink:label="loc_us-gaapGainLossOnInvestments_130" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapNonoperatingIncomeExpenseAbstract_130" xlink:to="loc_us-gaapGainLossOnInvestments_130" xlink:type="arc" order="11" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_GainsLossesOnExtinguishmentOfDebt" xlink:label="loc_us-gaapGainsLossesOnExtinguishmentOfDebt_130" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapNonoperatingIncomeExpenseAbstract_130" xlink:to="loc_us-gaapGainsLossesOnExtinguishmentOfDebt_130" xlink:type="arc" order="12" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherNonoperatingIncomeExpense" xlink:label="loc_us-gaapOtherNonoperatingIncomeExpense_130" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapNonoperatingIncomeExpenseAbstract_130" xlink:to="loc_us-gaapOtherNonoperatingIncomeExpense_130" xlink:type="arc" order="13" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NonoperatingIncomeExpense" xlink:label="loc_us-gaapNonoperatingIncomeExpense_130" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapNonoperatingIncomeExpenseAbstract_130" xlink:to="loc_us-gaapNonoperatingIncomeExpense_130" xlink:type="arc" order="14" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest" xlink:label="loc_us-gaapIncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_130" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapNonoperatingIncomeExpenseAbstract_130" xlink:to="loc_us-gaapIncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_130" xlink:type="arc" order="15" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeTaxExpenseBenefit" xlink:label="loc_us-gaapIncomeTaxExpenseBenefit_130" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapNonoperatingIncomeExpenseAbstract_130" xlink:to="loc_us-gaapIncomeTaxExpenseBenefit_130" xlink:type="arc" order="16" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NetIncomeLoss" xlink:label="loc_us-gaapNetIncomeLoss_130" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapNonoperatingIncomeExpenseAbstract_130" xlink:to="loc_us-gaapNetIncomeLoss_130" xlink:type="arc" order="17" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EarningsPerShareBasic" xlink:label="loc_us-gaapEarningsPerShareBasic_130" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapNonoperatingIncomeExpenseAbstract_130" xlink:to="loc_us-gaapEarningsPerShareBasic_130" xlink:type="arc" order="18" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EarningsPerShareDiluted" xlink:label="loc_us-gaapEarningsPerShareDiluted_130" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapNonoperatingIncomeExpenseAbstract_130" xlink:to="loc_us-gaapEarningsPerShareDiluted_130" xlink:type="arc" order="19" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_WeightedAverageNumberOfSharesOutstandingBasic" xlink:label="loc_us-gaapWeightedAverageNumberOfSharesOutstandingBasic_130" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapNonoperatingIncomeExpenseAbstract_130" xlink:to="loc_us-gaapWeightedAverageNumberOfSharesOutstandingBasic_130" xlink:type="arc" order="20" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding" xlink:label="loc_us-gaapWeightedAverageNumberOfDilutedSharesOutstanding_130" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapNonoperatingIncomeExpenseAbstract_130" xlink:to="loc_us-gaapWeightedAverageNumberOfDilutedSharesOutstanding_130" xlink:type="arc" order="21" />
    </link:definitionLink>
    <link:definitionLink xlink:type="extended" xlink:role="http://harrow.com/role/StatementsOfStockholdersEquity" xlink:title="00000005 - Statement - Condensed Consolidated Statements of Stockholders&apos; Equity (Unaudited)">
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaapStatementLineItems" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaapStatementTable" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xbrldt:contextElement="segment" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapStatementTable" xlink:type="arc" order="10" xbrldt:closed="true" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementEquityComponentsAxis" xlink:label="loc_us-gaapStatementEquityComponentsAxis" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaapStatementTable" xlink:to="loc_us-gaapStatementEquityComponentsAxis" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityComponentDomain" xlink:label="loc_us-gaapEquityComponentDomain" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaapStatementEquityComponentsAxis" xlink:to="loc_us-gaapEquityComponentDomain" xlink:type="arc" order="20" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityComponentDomain" xlink:label="loc_us-gaapEquityComponentDomain_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xbrldt:contextElement="segment" xlink:from="loc_us-gaapStatementEquityComponentsAxis" xlink:to="loc_us-gaapEquityComponentDomain_10" xlink:type="arc" order="30" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockMember" xlink:label="loc_us-gaapCommonStockMember_0" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapEquityComponentDomain" xlink:to="loc_us-gaapCommonStockMember_0" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AdditionalPaidInCapitalMember" xlink:label="loc_us-gaapAdditionalPaidInCapitalMember_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapEquityComponentDomain" xlink:to="loc_us-gaapAdditionalPaidInCapitalMember_10" xlink:type="arc" order="11" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RetainedEarningsMember" xlink:label="loc_us-gaapRetainedEarningsMember_20" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapEquityComponentDomain" xlink:to="loc_us-gaapRetainedEarningsMember_20" xlink:type="arc" order="21" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ParentMember" xlink:label="loc_us-gaapParentMember_30" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapEquityComponentDomain" xlink:to="loc_us-gaapParentMember_30" xlink:type="arc" order="31" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NoncontrollingInterestMember" xlink:label="loc_us-gaapNoncontrollingInterestMember_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapEquityComponentDomain" xlink:to="loc_us-gaapNoncontrollingInterestMember_40" xlink:type="arc" order="41" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest" xlink:label="loc_us-gaapStockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_70" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapStockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_70" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SharesOutstanding" xlink:label="loc_us-gaapSharesOutstanding_70" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapSharesOutstanding_70" xlink:type="arc" order="2" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised" xlink:label="loc_us-gaapStockIssuedDuringPeriodValueStockOptionsExercised_70" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapStockIssuedDuringPeriodValueStockOptionsExercised_70" xlink:type="arc" order="3" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised" xlink:label="loc_us-gaapStockIssuedDuringPeriodSharesStockOptionsExercised_70" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapStockIssuedDuringPeriodSharesStockOptionsExercised_70" xlink:type="arc" order="4" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockIssuedDuringPeriodValueRestrictedStockAwardGross" xlink:label="loc_us-gaapStockIssuedDuringPeriodValueRestrictedStockAwardGross_70" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapStockIssuedDuringPeriodValueRestrictedStockAwardGross_70" xlink:type="arc" order="5" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardGross" xlink:label="loc_us-gaapStockIssuedDuringPeriodSharesRestrictedStockAwardGross_70" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapStockIssuedDuringPeriodSharesRestrictedStockAwardGross_70" xlink:type="arc" order="6" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockIssuedDuringPeriodValueOther" xlink:label="loc_us-gaapStockIssuedDuringPeriodValueOther_70" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapStockIssuedDuringPeriodValueOther_70" xlink:type="arc" order="7" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockIssuedDuringPeriodSharesOther" xlink:label="loc_us-gaapStockIssuedDuringPeriodSharesOther_70" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapStockIssuedDuringPeriodSharesOther_70" xlink:type="arc" order="8" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue" xlink:label="loc_us-gaapAdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_70" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapAdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_70" xlink:type="arc" order="9" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NetIncomeLoss" xlink:label="loc_us-gaapNetIncomeLoss_70" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapNetIncomeLoss_70" xlink:type="arc" order="10" />
    </link:definitionLink>
    <link:definitionLink xlink:type="extended" xlink:role="http://harrow.com/role/StatementsOfCashFlows" xlink:title="00000006 - Statement - Condensed Consolidated Statements of Cash Flows (Unaudited)" />
    <link:definitionLink xlink:type="extended" xlink:role="http://harrow.com/role/DescriptionOfBusinessAndBasisOfPresentation" xlink:title="999012 - Disclosure - DESCRIPTION OF BUSINESS AND BASIS OF PRESENTATION" />
    <link:definitionLink xlink:type="extended" xlink:role="http://harrow.com/role/SummaryOfSignificantAccountingPolicies" xlink:title="999013 - Disclosure - SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES" />
    <link:definitionLink xlink:type="extended" xlink:role="http://harrow.com/role/Revenues" xlink:title="999014 - Disclosure - REVENUES" />
    <link:definitionLink xlink:type="extended" xlink:role="http://harrow.com/role/Inventories" xlink:title="999015 - Disclosure - INVENTORIES" />
    <link:definitionLink xlink:type="extended" xlink:role="http://harrow.com/role/PrepaidExpensesAndOtherCurrentAssets" xlink:title="999016 - Disclosure - PREPAID EXPENSES AND OTHER CURRENT ASSETS" />
    <link:definitionLink xlink:type="extended" xlink:role="http://harrow.com/role/PropertyPlantAndEquipment" xlink:title="999017 - Disclosure - PROPERTY, PLANT AND EQUIPMENT" />
    <link:definitionLink xlink:type="extended" xlink:role="http://harrow.com/role/CapitalizedSoftwareCosts" xlink:title="999018 - Disclosure - CAPITALIZED SOFTWARE COSTS" />
    <link:definitionLink xlink:type="extended" xlink:role="http://harrow.com/role/IntangibleAssetsAndGoodwill" xlink:title="999019 - Disclosure - INTANGIBLE ASSETS AND GOODWILL" />
    <link:definitionLink xlink:type="extended" xlink:role="http://harrow.com/role/AccountsPayableAndAccruedExpenses" xlink:title="999020 - Disclosure - ACCOUNTS PAYABLE AND ACCRUED EXPENSES" />
    <link:definitionLink xlink:type="extended" xlink:role="http://harrow.com/role/Debt" xlink:title="999021 - Disclosure - DEBT" />
    <link:definitionLink xlink:type="extended" xlink:role="http://harrow.com/role/Leases" xlink:title="999022 - Disclosure - LEASES" />
    <link:definitionLink xlink:type="extended" xlink:role="http://harrow.com/role/StockholdersEquityAndStock-basedCompensation" xlink:title="999023 - Disclosure - STOCKHOLDERS&#8217; EQUITY AND STOCK-BASED COMPENSATION" />
    <link:definitionLink xlink:type="extended" xlink:role="http://harrow.com/role/CommitmentsAndContingencies" xlink:title="999024 - Disclosure - COMMITMENTS AND CONTINGENCIES" />
    <link:definitionLink xlink:type="extended" xlink:role="http://harrow.com/role/SegmentsAndConcentrations" xlink:title="999025 - Disclosure - SEGMENTS AND CONCENTRATIONS" />
    <link:definitionLink xlink:type="extended" xlink:role="http://harrow.com/role/SubsequentEvents" xlink:title="999026 - Disclosure - SUBSEQUENT EVENTS" />
    <link:definitionLink xlink:type="extended" xlink:role="http://harrow.com/role/SummaryOfSignificantAccountingPoliciesPolicies" xlink:title="999027 - Disclosure - SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Policies)" />
    <link:definitionLink xlink:type="extended" xlink:role="http://harrow.com/role/SummaryOfSignificantAccountingPoliciesTables" xlink:title="999028 - Disclosure - SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Tables)" />
    <link:definitionLink xlink:type="extended" xlink:role="http://harrow.com/role/RevenuesTables" xlink:title="999029 - Disclosure - REVENUES (Tables)" />
    <link:definitionLink xlink:type="extended" xlink:role="http://harrow.com/role/InventoriesTables" xlink:title="999030 - Disclosure - INVENTORIES (Tables)" />
    <link:definitionLink xlink:type="extended" xlink:role="http://harrow.com/role/PrepaidExpensesAndOtherCurrentAssetsTables" xlink:title="999031 - Disclosure - PREPAID EXPENSES AND OTHER CURRENT ASSETS (Tables)" />
    <link:definitionLink xlink:type="extended" xlink:role="http://harrow.com/role/PropertyPlantAndEquipmentTables" xlink:title="999032 - Disclosure - PROPERTY, PLANT AND EQUIPMENT (Tables)" />
    <link:definitionLink xlink:type="extended" xlink:role="http://harrow.com/role/CapitalizedSoftwareCostsTables" xlink:title="999033 - Disclosure - CAPITALIZED SOFTWARE COSTS (Tables)" />
    <link:definitionLink xlink:type="extended" xlink:role="http://harrow.com/role/IntangibleAssetsAndGoodwillTables" xlink:title="999034 - Disclosure - INTANGIBLE ASSETS AND GOODWILL (Tables)" />
    <link:definitionLink xlink:type="extended" xlink:role="http://harrow.com/role/AccountsPayableAndAccruedExpensesTables" xlink:title="999035 - Disclosure - ACCOUNTS PAYABLE AND ACCRUED EXPENSES (Tables)" />
    <link:definitionLink xlink:type="extended" xlink:role="http://harrow.com/role/DebtTables" xlink:title="999036 - Disclosure - DEBT (Tables)" />
    <link:definitionLink xlink:type="extended" xlink:role="http://harrow.com/role/LeasesTables" xlink:title="999037 - Disclosure - LEASES (Tables)" />
    <link:definitionLink xlink:type="extended" xlink:role="http://harrow.com/role/StockholdersEquityAndStock-basedCompensationTables" xlink:title="999038 - Disclosure - STOCKHOLDERS&#8217; EQUITY AND STOCK-BASED COMPENSATION (Tables)" />
    <link:definitionLink xlink:type="extended" xlink:role="http://harrow.com/role/SegmentsAndConcentrationsTables" xlink:title="999039 - Disclosure - SEGMENTS AND CONCENTRATIONS (Tables)" />
    <link:definitionLink xlink:type="extended" xlink:role="http://harrow.com/role/ScheduleOfAccountsReceivableAllowanceOfCreditLossDetails" xlink:title="999040 - Disclosure - SCHEDULE OF ACCOUNTS RECEIVABLE ALLOWANCE OF CREDIT LOSS (Details)" />
    <link:definitionLink xlink:type="extended" xlink:role="http://harrow.com/role/ScheduleOfEstimatedFairValueDetails" xlink:title="999041 - Disclosure - SCHEDULE OF ESTIMATED FAIR VALUE (Details)">
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_PlatformOperatorCryptoAssetLineItems" xlink:label="loc_srtPlatformOperatorCryptoAssetLineItems" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_PlatformOperatorCryptoAssetTable" xlink:label="loc_srtPlatformOperatorCryptoAssetTable" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xbrldt:contextElement="segment" xlink:from="loc_srtPlatformOperatorCryptoAssetLineItems" xlink:to="loc_srtPlatformOperatorCryptoAssetTable" xlink:type="arc" order="10" xbrldt:closed="true" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:label="loc_us-gaapFairValueByFairValueHierarchyLevelAxis" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_srtPlatformOperatorCryptoAssetTable" xlink:to="loc_us-gaapFairValueByFairValueHierarchyLevelAxis" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:label="loc_us-gaapFairValueMeasurementsFairValueHierarchyDomain" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaapFairValueByFairValueHierarchyLevelAxis" xlink:to="loc_us-gaapFairValueMeasurementsFairValueHierarchyDomain" xlink:type="arc" order="20" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:label="loc_us-gaapFairValueMeasurementsFairValueHierarchyDomain_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xbrldt:contextElement="segment" xlink:from="loc_us-gaapFairValueByFairValueHierarchyLevelAxis" xlink:to="loc_us-gaapFairValueMeasurementsFairValueHierarchyDomain_10" xlink:type="arc" order="30" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueInputsLevel1Member" xlink:label="loc_us-gaapFairValueInputsLevel1Member_0" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapFairValueMeasurementsFairValueHierarchyDomain" xlink:to="loc_us-gaapFairValueInputsLevel1Member_0" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueInputsLevel2Member" xlink:label="loc_us-gaapFairValueInputsLevel2Member_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapFairValueMeasurementsFairValueHierarchyDomain" xlink:to="loc_us-gaapFairValueInputsLevel2Member_40" xlink:type="arc" order="41" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentAxis" xlink:label="loc_us-gaapDebtInstrumentAxis" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_srtPlatformOperatorCryptoAssetTable" xlink:to="loc_us-gaapDebtInstrumentAxis" xlink:type="arc" order="2" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentNameDomain" xlink:label="loc_us-gaapDebtInstrumentNameDomain" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaapDebtInstrumentAxis" xlink:to="loc_us-gaapDebtInstrumentNameDomain" xlink:type="arc" order="20" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentNameDomain" xlink:label="loc_us-gaapDebtInstrumentNameDomain_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xbrldt:contextElement="segment" xlink:from="loc_us-gaapDebtInstrumentAxis" xlink:to="loc_us-gaapDebtInstrumentNameDomain_10" xlink:type="arc" order="30" />
      <link:loc xlink:type="locator" xlink:href="hrow-20250930.xsd#HROW_TwoThousandAndTwentySixNotesMember" xlink:label="loc_HROWTwoThousandAndTwentySixNotesMember_0" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapDebtInstrumentNameDomain" xlink:to="loc_HROWTwoThousandAndTwentySixNotesMember_0" xlink:type="arc" order="2" />
      <link:loc xlink:type="locator" xlink:href="hrow-20250930.xsd#HROW_TwoThousandAndTwentySevenNotesMember" xlink:label="loc_HROWTwoThousandAndTwentySevenNotesMember_20" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapDebtInstrumentNameDomain" xlink:to="loc_HROWTwoThousandAndTwentySevenNotesMember_20" xlink:type="arc" order="22" />
      <link:loc xlink:type="locator" xlink:href="hrow-20250930.xsd#HROW_OaktreeLoanMember" xlink:label="loc_HROWOaktreeLoanMember_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapDebtInstrumentNameDomain" xlink:to="loc_HROWOaktreeLoanMember_40" xlink:type="arc" order="42" />
      <link:loc xlink:type="locator" xlink:href="hrow-20250930.xsd#HROW_TwoThousandAndThirtyNotesMember" xlink:label="loc_HROWTwoThousandAndThirtyNotesMember_60" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapDebtInstrumentNameDomain" xlink:to="loc_HROWTwoThousandAndThirtyNotesMember_60" xlink:type="arc" order="62" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentCarryingAmount" xlink:label="loc_us-gaapDebtInstrumentCarryingAmount_90" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srtPlatformOperatorCryptoAssetLineItems" xlink:to="loc_us-gaapDebtInstrumentCarryingAmount_90" xlink:type="arc" order="0" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentFairValue" xlink:label="loc_us-gaapDebtInstrumentFairValue_90" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srtPlatformOperatorCryptoAssetLineItems" xlink:to="loc_us-gaapDebtInstrumentFairValue_90" xlink:type="arc" order="1" />
    </link:definitionLink>
    <link:definitionLink xlink:type="extended" xlink:role="http://harrow.com/role/DescriptionOfBusinessAndBasisOfPresentationDetailsNarrative" xlink:title="999042 - Disclosure - DESCRIPTION OF BUSINESS AND BASIS OF PRESENTATION (Details Narrative)" />
    <link:definitionLink xlink:type="extended" xlink:role="http://harrow.com/role/ScheduleOfBasicEarningsPerCommonShareDetails" xlink:title="999043 - Disclosure - SCHEDULE OF BASIC EARNINGS PER COMMON SHARE (Details)" />
    <link:definitionLink xlink:type="extended" xlink:role="http://harrow.com/role/ScheduleOfDilutedNetIncomePerShareDetails" xlink:title="999044 - Disclosure - SCHEDULE OF DILUTED NET INCOME PER SHARE (Details)">
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems" xlink:label="loc_us-gaapAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable" xlink:label="loc_us-gaapScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xbrldt:contextElement="segment" xlink:from="loc_us-gaapAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems" xlink:to="loc_us-gaapScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable" xlink:type="arc" order="10" xbrldt:closed="true" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis" xlink:label="loc_us-gaapAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaapScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable" xlink:to="loc_us-gaapAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AntidilutiveSecuritiesNameDomain" xlink:label="loc_us-gaapAntidilutiveSecuritiesNameDomain" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaapAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis" xlink:to="loc_us-gaapAntidilutiveSecuritiesNameDomain" xlink:type="arc" order="20" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AntidilutiveSecuritiesNameDomain" xlink:label="loc_us-gaapAntidilutiveSecuritiesNameDomain_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xbrldt:contextElement="segment" xlink:from="loc_us-gaapAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis" xlink:to="loc_us-gaapAntidilutiveSecuritiesNameDomain_10" xlink:type="arc" order="30" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestrictedStockMember" xlink:label="loc_us-gaapRestrictedStockMember_0" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapAntidilutiveSecuritiesNameDomain" xlink:to="loc_us-gaapRestrictedStockMember_0" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockOptionMember" xlink:label="loc_us-gaapStockOptionMember_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapAntidilutiveSecuritiesNameDomain" xlink:to="loc_us-gaapStockOptionMember_10" xlink:type="arc" order="11" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount" xlink:label="loc_us-gaapAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems" xlink:to="loc_us-gaapAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_40" xlink:type="arc" order="0" />
    </link:definitionLink>
    <link:definitionLink xlink:type="extended" xlink:role="http://harrow.com/role/ScheduleOfBasicAndDilutedEarningsPerCommonShareDetails" xlink:title="999045 - Disclosure - SCHEDULE OF BASIC AND DILUTED EARNINGS PER COMMON SHARE (Details)" />
    <link:definitionLink xlink:type="extended" xlink:role="http://harrow.com/role/SummaryOfSignificantAccountingPoliciesDetailsNarrative" xlink:title="999046 - Disclosure - SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details Narrative)">
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems" xlink:label="loc_us-gaapAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable" xlink:label="loc_us-gaapScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xbrldt:contextElement="segment" xlink:from="loc_us-gaapAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems" xlink:to="loc_us-gaapScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable" xlink:type="arc" order="10" xbrldt:closed="true" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis" xlink:label="loc_us-gaapAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaapScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable" xlink:to="loc_us-gaapAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AntidilutiveSecuritiesNameDomain" xlink:label="loc_us-gaapAntidilutiveSecuritiesNameDomain" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaapAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis" xlink:to="loc_us-gaapAntidilutiveSecuritiesNameDomain" xlink:type="arc" order="20" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AntidilutiveSecuritiesNameDomain" xlink:label="loc_us-gaapAntidilutiveSecuritiesNameDomain_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xbrldt:contextElement="segment" xlink:from="loc_us-gaapAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis" xlink:to="loc_us-gaapAntidilutiveSecuritiesNameDomain_10" xlink:type="arc" order="30" />
      <link:loc xlink:type="locator" xlink:href="hrow-20250930.xsd#HROW_StockOptionsUnvestedRSUsAndUnvestedPSUsMember" xlink:label="loc_HROWStockOptionsUnvestedRSUsAndUnvestedPSUsMember_0" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapAntidilutiveSecuritiesNameDomain" xlink:to="loc_HROWStockOptionsUnvestedRSUsAndUnvestedPSUsMember_0" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AwardTypeAxis" xlink:label="loc_us-gaapAwardTypeAxis" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaapScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable" xlink:to="loc_us-gaapAwardTypeAxis" xlink:type="arc" order="2" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="loc_us-gaapShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaapAwardTypeAxis" xlink:to="loc_us-gaapShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:type="arc" order="20" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="loc_us-gaapShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xbrldt:contextElement="segment" xlink:from="loc_us-gaapAwardTypeAxis" xlink:to="loc_us-gaapShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_10" xlink:type="arc" order="30" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestrictedStockUnitsRSUMember" xlink:label="loc_us-gaapRestrictedStockUnitsRSUMember_20" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:to="loc_us-gaapRestrictedStockUnitsRSUMember_20" xlink:type="arc" order="21" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_TitleOfIndividualAxis" xlink:label="loc_srtTitleOfIndividualAxis" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaapScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable" xlink:to="loc_srtTitleOfIndividualAxis" xlink:type="arc" order="3" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_TitleOfIndividualWithRelationshipToEntityDomain" xlink:label="loc_srtTitleOfIndividualWithRelationshipToEntityDomain" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srtTitleOfIndividualAxis" xlink:to="loc_srtTitleOfIndividualWithRelationshipToEntityDomain" xlink:type="arc" order="20" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_TitleOfIndividualWithRelationshipToEntityDomain" xlink:label="loc_srtTitleOfIndividualWithRelationshipToEntityDomain_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xbrldt:contextElement="segment" xlink:from="loc_srtTitleOfIndividualAxis" xlink:to="loc_srtTitleOfIndividualWithRelationshipToEntityDomain_10" xlink:type="arc" order="30" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_DirectorMember" xlink:label="loc_srtDirectorMember_20" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srtTitleOfIndividualWithRelationshipToEntityDomain" xlink:to="loc_srtDirectorMember_20" xlink:type="arc" order="22" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount" xlink:label="loc_us-gaapAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_90" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems" xlink:to="loc_us-gaapAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_90" xlink:type="arc" order="0" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardGross" xlink:label="loc_us-gaapStockIssuedDuringPeriodSharesRestrictedStockAwardGross_90" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems" xlink:to="loc_us-gaapStockIssuedDuringPeriodSharesRestrictedStockAwardGross_90" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EffectiveIncomeTaxRateReconciliationStateAndLocalIncomeTaxes" xlink:label="loc_us-gaapEffectiveIncomeTaxRateReconciliationStateAndLocalIncomeTaxes_90" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems" xlink:to="loc_us-gaapEffectiveIncomeTaxRateReconciliationStateAndLocalIncomeTaxes_90" xlink:type="arc" order="2" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate" xlink:label="loc_us-gaapEffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate_90" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems" xlink:to="loc_us-gaapEffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate_90" xlink:type="arc" order="3" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_UnrecognizedTaxBenefits" xlink:label="loc_us-gaapUnrecognizedTaxBenefits_90" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems" xlink:to="loc_us-gaapUnrecognizedTaxBenefits_90" xlink:type="arc" order="4" />
    </link:definitionLink>
    <link:definitionLink xlink:type="extended" xlink:role="http://harrow.com/role/ScheduleOfAccrualsAndAllowancesDetails" xlink:title="999047 - Disclosure - SCHEDULE OF ACCRUALS AND ALLOWANCES (Details)">
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ValuationAndQualifyingAccountsDisclosureLineItems" xlink:label="loc_srtValuationAndQualifyingAccountsDisclosureLineItems" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ValuationAndQualifyingAccountsDisclosureTable" xlink:label="loc_srtValuationAndQualifyingAccountsDisclosureTable" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xbrldt:contextElement="segment" xlink:from="loc_srtValuationAndQualifyingAccountsDisclosureLineItems" xlink:to="loc_srtValuationAndQualifyingAccountsDisclosureTable" xlink:type="arc" order="10" xbrldt:closed="true" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ValuationAllowancesAndReservesTypeAxis" xlink:label="loc_us-gaapValuationAllowancesAndReservesTypeAxis" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_srtValuationAndQualifyingAccountsDisclosureTable" xlink:to="loc_us-gaapValuationAllowancesAndReservesTypeAxis" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ValuationAllowancesAndReservesDomain" xlink:label="loc_us-gaapValuationAllowancesAndReservesDomain" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaapValuationAllowancesAndReservesTypeAxis" xlink:to="loc_us-gaapValuationAllowancesAndReservesDomain" xlink:type="arc" order="20" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ValuationAllowancesAndReservesDomain" xlink:label="loc_us-gaapValuationAllowancesAndReservesDomain_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xbrldt:contextElement="segment" xlink:from="loc_us-gaapValuationAllowancesAndReservesTypeAxis" xlink:to="loc_us-gaapValuationAllowancesAndReservesDomain_10" xlink:type="arc" order="30" />
      <link:loc xlink:type="locator" xlink:href="hrow-20250930.xsd#HROW_ChargebacksMember" xlink:label="loc_HROWChargebacksMember_0" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapValuationAllowancesAndReservesDomain" xlink:to="loc_HROWChargebacksMember_0" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="hrow-20250930.xsd#HROW_GovernmentRebatesMember" xlink:label="loc_HROWGovernmentRebatesMember_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapValuationAllowancesAndReservesDomain" xlink:to="loc_HROWGovernmentRebatesMember_10" xlink:type="arc" order="11" />
      <link:loc xlink:type="locator" xlink:href="hrow-20250930.xsd#HROW_AllowancesForSalesReturnsMember" xlink:label="loc_HROWAllowancesForSalesReturnsMember_20" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapValuationAllowancesAndReservesDomain" xlink:to="loc_HROWAllowancesForSalesReturnsMember_20" xlink:type="arc" order="21" />
      <link:loc xlink:type="locator" xlink:href="hrow-20250930.xsd#HROW_AdministrativeFeesAndOtherRebatesMember" xlink:label="loc_HROWAdministrativeFeesAndOtherRebatesMember_30" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapValuationAllowancesAndReservesDomain" xlink:to="loc_HROWAdministrativeFeesAndOtherRebatesMember_30" xlink:type="arc" order="31" />
      <link:loc xlink:type="locator" xlink:href="hrow-20250930.xsd#HROW_CoPayAssistanceMember" xlink:label="loc_HROWCoPayAssistanceMember_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapValuationAllowancesAndReservesDomain" xlink:to="loc_HROWCoPayAssistanceMember_40" xlink:type="arc" order="41" />
      <link:loc xlink:type="locator" xlink:href="hrow-20250930.xsd#HROW_ReservesForCashDiscountMember" xlink:label="loc_HROWReservesForCashDiscountMember_50" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapValuationAllowancesAndReservesDomain" xlink:to="loc_HROWReservesForCashDiscountMember_50" xlink:type="arc" order="51" />
      <link:loc xlink:type="locator" xlink:href="hrow-20250930.xsd#HROW_GainLossOnValuationAllowancesAndReservesBalance" xlink:label="loc_HROWGainLossOnValuationAllowancesAndReservesBalance_430" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srtValuationAndQualifyingAccountsDisclosureLineItems" xlink:to="loc_HROWGainLossOnValuationAllowancesAndReservesBalance_430" xlink:type="arc" order="0" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ValuationAllowancesAndReservesAdjustments" xlink:label="loc_us-gaapValuationAllowancesAndReservesAdjustments_430" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srtValuationAndQualifyingAccountsDisclosureLineItems" xlink:to="loc_us-gaapValuationAllowancesAndReservesAdjustments_430" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ValuationAllowancesAndReservesDeductions" xlink:label="loc_us-gaapValuationAllowancesAndReservesDeductions_430" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srtValuationAndQualifyingAccountsDisclosureLineItems" xlink:to="loc_us-gaapValuationAllowancesAndReservesDeductions_430" xlink:type="arc" order="2" />
    </link:definitionLink>
    <link:definitionLink xlink:type="extended" xlink:role="http://harrow.com/role/ScheduleOfDisaggregatedRevenueDetails" xlink:title="999048 - Disclosure - SCHEDULE OF DISAGGREGATED REVENUE (Details)">
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisaggregationOfRevenueLineItems" xlink:label="loc_us-gaapDisaggregationOfRevenueLineItems" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisaggregationOfRevenueTable" xlink:label="loc_us-gaapDisaggregationOfRevenueTable" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xbrldt:contextElement="segment" xlink:from="loc_us-gaapDisaggregationOfRevenueLineItems" xlink:to="loc_us-gaapDisaggregationOfRevenueTable" xlink:type="arc" order="10" xbrldt:closed="true" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ProductOrServiceAxis" xlink:label="loc_srtProductOrServiceAxis" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaapDisaggregationOfRevenueTable" xlink:to="loc_srtProductOrServiceAxis" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ProductsAndServicesDomain" xlink:label="loc_srtProductsAndServicesDomain" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srtProductOrServiceAxis" xlink:to="loc_srtProductsAndServicesDomain" xlink:type="arc" order="20" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ProductsAndServicesDomain" xlink:label="loc_srtProductsAndServicesDomain_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xbrldt:contextElement="segment" xlink:from="loc_srtProductOrServiceAxis" xlink:to="loc_srtProductsAndServicesDomain_10" xlink:type="arc" order="30" />
      <link:loc xlink:type="locator" xlink:href="hrow-20250930.xsd#HROW_ProductSalesNetMember" xlink:label="loc_HROWProductSalesNetMember_0" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srtProductsAndServicesDomain" xlink:to="loc_HROWProductSalesNetMember_0" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="hrow-20250930.xsd#HROW_OtherRevenuesMember" xlink:label="loc_HROWOtherRevenuesMember_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srtProductsAndServicesDomain" xlink:to="loc_HROWOtherRevenuesMember_40" xlink:type="arc" order="41" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax" xlink:label="loc_us-gaapRevenueFromContractWithCustomerExcludingAssessedTax_130" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapDisaggregationOfRevenueLineItems" xlink:to="loc_us-gaapRevenueFromContractWithCustomerExcludingAssessedTax_130" xlink:type="arc" order="0" />
    </link:definitionLink>
    <link:definitionLink xlink:type="extended" xlink:role="http://harrow.com/role/RevenuesDetailsNarrative" xlink:title="999049 - Disclosure - REVENUES (Details Narrative)" />
    <link:definitionLink xlink:type="extended" xlink:role="http://harrow.com/role/ScheduleOfInventoriesDetails" xlink:title="999050 - Disclosure - SCHEDULE OF INVENTORIES (Details)" />
    <link:definitionLink xlink:type="extended" xlink:role="http://harrow.com/role/ScheduleOfPrepaidExpensesAndOtherCurrentAssetsDetails" xlink:title="999051 - Disclosure - SCHEDULE OF PREPAID EXPENSES AND OTHER CURRENT ASSETS (Details)" />
    <link:definitionLink xlink:type="extended" xlink:role="http://harrow.com/role/ScheduleOfPropertyPlantAndEquipmentDetails" xlink:title="999052 - Disclosure - SCHEDULE OF PROPERTY, PLANT AND EQUIPMENT (Details)" />
    <link:definitionLink xlink:type="extended" xlink:role="http://harrow.com/role/PropertyPlantAndEquipmentDetailsNarrative" xlink:title="999053 - Disclosure - PROPERTY, PLANT AND EQUIPMENT (Details Narrative)" />
    <link:definitionLink xlink:type="extended" xlink:role="http://harrow.com/role/ScheduleOfCapitalizedSoftwareCostsDetails" xlink:title="999054 - Disclosure - SCHEDULE OF CAPITALIZED SOFTWARE COSTS (Details)">
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsLineItems" xlink:label="loc_us-gaapFiniteLivedIntangibleAssetsLineItems" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable" xlink:label="loc_us-gaapScheduleOfFiniteLivedIntangibleAssetsTable" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xbrldt:contextElement="segment" xlink:from="loc_us-gaapFiniteLivedIntangibleAssetsLineItems" xlink:to="loc_us-gaapScheduleOfFiniteLivedIntangibleAssetsTable" xlink:type="arc" order="10" xbrldt:closed="true" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis" xlink:label="loc_us-gaapFiniteLivedIntangibleAssetsByMajorClassAxis" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaapScheduleOfFiniteLivedIntangibleAssetsTable" xlink:to="loc_us-gaapFiniteLivedIntangibleAssetsByMajorClassAxis" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:label="loc_us-gaapFiniteLivedIntangibleAssetsMajorClassNameDomain" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaapFiniteLivedIntangibleAssetsByMajorClassAxis" xlink:to="loc_us-gaapFiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:type="arc" order="20" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:label="loc_us-gaapFiniteLivedIntangibleAssetsMajorClassNameDomain_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xbrldt:contextElement="segment" xlink:from="loc_us-gaapFiniteLivedIntangibleAssetsByMajorClassAxis" xlink:to="loc_us-gaapFiniteLivedIntangibleAssetsMajorClassNameDomain_10" xlink:type="arc" order="30" />
      <link:loc xlink:type="locator" xlink:href="hrow-20250930.xsd#HROW_CapitalizedSoftwareDevelopmentCostsMember" xlink:label="loc_HROWCapitalizedSoftwareDevelopmentCostsMember_0" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapFiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:to="loc_HROWCapitalizedSoftwareDevelopmentCostsMember_0" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="hrow-20250930.xsd#HROW_ThirdPartySoftwareLicenseMember" xlink:label="loc_HROWThirdPartySoftwareLicenseMember_20" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapFiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:to="loc_HROWThirdPartySoftwareLicenseMember_20" xlink:type="arc" order="21" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CapitalizedComputerSoftwareGross" xlink:label="loc_us-gaapCapitalizedComputerSoftwareGross_70" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapFiniteLivedIntangibleAssetsLineItems" xlink:to="loc_us-gaapCapitalizedComputerSoftwareGross_70" xlink:type="arc" order="0" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CapitalizedComputerSoftwareAccumulatedAmortization" xlink:label="loc_us-gaapCapitalizedComputerSoftwareAccumulatedAmortization_70" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapFiniteLivedIntangibleAssetsLineItems" xlink:to="loc_us-gaapCapitalizedComputerSoftwareAccumulatedAmortization_70" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CapitalizedComputerSoftwareNet" xlink:label="loc_us-gaapCapitalizedComputerSoftwareNet_70" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapFiniteLivedIntangibleAssetsLineItems" xlink:to="loc_us-gaapCapitalizedComputerSoftwareNet_70" xlink:type="arc" order="2" />
    </link:definitionLink>
    <link:definitionLink xlink:type="extended" xlink:role="http://harrow.com/role/CapitalizedSoftwareCostsDetailsNarrative" xlink:title="999055 - Disclosure - CAPITALIZED SOFTWARE COSTS (Details Narrative)">
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsLineItems" xlink:label="loc_us-gaapFiniteLivedIntangibleAssetsLineItems" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable" xlink:label="loc_us-gaapScheduleOfFiniteLivedIntangibleAssetsTable" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xbrldt:contextElement="segment" xlink:from="loc_us-gaapFiniteLivedIntangibleAssetsLineItems" xlink:to="loc_us-gaapScheduleOfFiniteLivedIntangibleAssetsTable" xlink:type="arc" order="10" xbrldt:closed="true" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis" xlink:label="loc_us-gaapFiniteLivedIntangibleAssetsByMajorClassAxis" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaapScheduleOfFiniteLivedIntangibleAssetsTable" xlink:to="loc_us-gaapFiniteLivedIntangibleAssetsByMajorClassAxis" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:label="loc_us-gaapFiniteLivedIntangibleAssetsMajorClassNameDomain" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaapFiniteLivedIntangibleAssetsByMajorClassAxis" xlink:to="loc_us-gaapFiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:type="arc" order="20" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:label="loc_us-gaapFiniteLivedIntangibleAssetsMajorClassNameDomain_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xbrldt:contextElement="segment" xlink:from="loc_us-gaapFiniteLivedIntangibleAssetsByMajorClassAxis" xlink:to="loc_us-gaapFiniteLivedIntangibleAssetsMajorClassNameDomain_10" xlink:type="arc" order="30" />
      <link:loc xlink:type="locator" xlink:href="hrow-20250930.xsd#HROW_CapitalizedSoftwareDevelopmentCostsMember" xlink:label="loc_HROWCapitalizedSoftwareDevelopmentCostsMember_0" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapFiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:to="loc_HROWCapitalizedSoftwareDevelopmentCostsMember_0" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AdjustmentForAmortization" xlink:label="loc_us-gaapAdjustmentForAmortization_50" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapFiniteLivedIntangibleAssetsLineItems" xlink:to="loc_us-gaapAdjustmentForAmortization_50" xlink:type="arc" order="0" />
    </link:definitionLink>
    <link:definitionLink xlink:type="extended" xlink:role="http://harrow.com/role/ScheduleOfIntangibleAssetsDetails" xlink:title="999056 - Disclosure - SCHEDULE OF INTANGIBLE ASSETS (Details)">
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsLineItems" xlink:label="loc_us-gaapFiniteLivedIntangibleAssetsLineItems" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable" xlink:label="loc_us-gaapScheduleOfFiniteLivedIntangibleAssetsTable" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xbrldt:contextElement="segment" xlink:from="loc_us-gaapFiniteLivedIntangibleAssetsLineItems" xlink:to="loc_us-gaapScheduleOfFiniteLivedIntangibleAssetsTable" xlink:type="arc" order="10" xbrldt:closed="true" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis" xlink:label="loc_us-gaapFiniteLivedIntangibleAssetsByMajorClassAxis" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaapScheduleOfFiniteLivedIntangibleAssetsTable" xlink:to="loc_us-gaapFiniteLivedIntangibleAssetsByMajorClassAxis" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:label="loc_us-gaapFiniteLivedIntangibleAssetsMajorClassNameDomain" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaapFiniteLivedIntangibleAssetsByMajorClassAxis" xlink:to="loc_us-gaapFiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:type="arc" order="20" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:label="loc_us-gaapFiniteLivedIntangibleAssetsMajorClassNameDomain_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xbrldt:contextElement="segment" xlink:from="loc_us-gaapFiniteLivedIntangibleAssetsByMajorClassAxis" xlink:to="loc_us-gaapFiniteLivedIntangibleAssetsMajorClassNameDomain_10" xlink:type="arc" order="30" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PatentsMember" xlink:label="loc_us-gaapPatentsMember_0" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapFiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:to="loc_us-gaapPatentsMember_0" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="hrow-20250930.xsd#HROW_LicensesMember" xlink:label="loc_HROWLicensesMember_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapFiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:to="loc_HROWLicensesMember_10" xlink:type="arc" order="11" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TrademarksMember" xlink:label="loc_us-gaapTrademarksMember_20" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapFiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:to="loc_us-gaapTrademarksMember_20" xlink:type="arc" order="21" />
      <link:loc xlink:type="locator" xlink:href="hrow-20250930.xsd#HROW_AcquiredNewDrugApplicationsMember" xlink:label="loc_HROWAcquiredNewDrugApplicationsMember_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapFiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:to="loc_HROWAcquiredNewDrugApplicationsMember_40" xlink:type="arc" order="41" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CustomerRelationshipsMember" xlink:label="loc_us-gaapCustomerRelationshipsMember_50" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapFiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:to="loc_us-gaapCustomerRelationshipsMember_50" xlink:type="arc" order="51" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TradeNamesMember" xlink:label="loc_us-gaapTradeNamesMember_60" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapFiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:to="loc_us-gaapTradeNamesMember_60" xlink:type="arc" order="61" />
      <link:loc xlink:type="locator" xlink:href="hrow-20250930.xsd#HROW_StatePharmacyLicensesMember" xlink:label="loc_HROWStatePharmacyLicensesMember_70" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapFiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:to="loc_HROWStatePharmacyLicensesMember_70" xlink:type="arc" order="71" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetUsefulLife" xlink:label="loc_us-gaapFiniteLivedIntangibleAssetUsefulLife_100" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapFiniteLivedIntangibleAssetsLineItems" xlink:to="loc_us-gaapFiniteLivedIntangibleAssetUsefulLife_100" xlink:type="arc" order="0" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsGross" xlink:label="loc_us-gaapFiniteLivedIntangibleAssetsGross_100" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapFiniteLivedIntangibleAssetsLineItems" xlink:to="loc_us-gaapFiniteLivedIntangibleAssetsGross_100" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization" xlink:label="loc_us-gaapFiniteLivedIntangibleAssetsAccumulatedAmortization_100" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapFiniteLivedIntangibleAssetsLineItems" xlink:to="loc_us-gaapFiniteLivedIntangibleAssetsAccumulatedAmortization_100" xlink:type="arc" order="2" />
      <link:loc xlink:type="locator" xlink:href="hrow-20250930.xsd#HROW_FiniteLivedIntangibleAssetsDisposal" xlink:label="loc_HROWFiniteLivedIntangibleAssetsDisposal_100" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapFiniteLivedIntangibleAssetsLineItems" xlink:to="loc_HROWFiniteLivedIntangibleAssetsDisposal_100" xlink:type="arc" order="3" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IntangibleAssetsNetExcludingGoodwill" xlink:label="loc_us-gaapIntangibleAssetsNetExcludingGoodwill_100" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapFiniteLivedIntangibleAssetsLineItems" xlink:to="loc_us-gaapIntangibleAssetsNetExcludingGoodwill_100" xlink:type="arc" order="4" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsAmortizationMethod" xlink:label="loc_us-gaapFiniteLivedIntangibleAssetsAmortizationMethod_100" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapFiniteLivedIntangibleAssetsLineItems" xlink:to="loc_us-gaapFiniteLivedIntangibleAssetsAmortizationMethod_100" xlink:type="arc" order="5" />
    </link:definitionLink>
    <link:definitionLink xlink:type="extended" xlink:role="http://harrow.com/role/ScheduleOfAmortizationExpensesForIntangibleAssetsDetails" xlink:title="999057 - Disclosure - SCHEDULE OF AMORTIZATION EXPENSES FOR INTANGIBLE ASSETS (Details)">
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsLineItems" xlink:label="loc_us-gaapFiniteLivedIntangibleAssetsLineItems" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable" xlink:label="loc_us-gaapScheduleOfFiniteLivedIntangibleAssetsTable" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xbrldt:contextElement="segment" xlink:from="loc_us-gaapFiniteLivedIntangibleAssetsLineItems" xlink:to="loc_us-gaapScheduleOfFiniteLivedIntangibleAssetsTable" xlink:type="arc" order="10" xbrldt:closed="true" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis" xlink:label="loc_us-gaapFiniteLivedIntangibleAssetsByMajorClassAxis" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaapScheduleOfFiniteLivedIntangibleAssetsTable" xlink:to="loc_us-gaapFiniteLivedIntangibleAssetsByMajorClassAxis" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:label="loc_us-gaapFiniteLivedIntangibleAssetsMajorClassNameDomain" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaapFiniteLivedIntangibleAssetsByMajorClassAxis" xlink:to="loc_us-gaapFiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:type="arc" order="20" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:label="loc_us-gaapFiniteLivedIntangibleAssetsMajorClassNameDomain_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xbrldt:contextElement="segment" xlink:from="loc_us-gaapFiniteLivedIntangibleAssetsByMajorClassAxis" xlink:to="loc_us-gaapFiniteLivedIntangibleAssetsMajorClassNameDomain_10" xlink:type="arc" order="30" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PatentsMember" xlink:label="loc_us-gaapPatentsMember_0" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapFiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:to="loc_us-gaapPatentsMember_0" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="hrow-20250930.xsd#HROW_LicensesMember" xlink:label="loc_HROWLicensesMember_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapFiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:to="loc_HROWLicensesMember_40" xlink:type="arc" order="41" />
      <link:loc xlink:type="locator" xlink:href="hrow-20250930.xsd#HROW_AcquiredProductRightsMember" xlink:label="loc_HROWAcquiredProductRightsMember_80" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapFiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:to="loc_HROWAcquiredProductRightsMember_80" xlink:type="arc" order="81" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TradeNamesMember" xlink:label="loc_us-gaapTradeNamesMember_120" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapFiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:to="loc_us-gaapTradeNamesMember_120" xlink:type="arc" order="121" />
      <link:loc xlink:type="locator" xlink:href="hrow-20250930.xsd#HROW_StatePharmacyLicenseMember" xlink:label="loc_HROWStatePharmacyLicenseMember_160" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapFiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:to="loc_HROWStatePharmacyLicenseMember_160" xlink:type="arc" order="161" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CustomerRelationshipsMember" xlink:label="loc_us-gaapCustomerRelationshipsMember_200" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapFiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:to="loc_us-gaapCustomerRelationshipsMember_200" xlink:type="arc" order="201" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AmortizationOfIntangibleAssets" xlink:label="loc_us-gaapAmortizationOfIntangibleAssets_290" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapFiniteLivedIntangibleAssetsLineItems" xlink:to="loc_us-gaapAmortizationOfIntangibleAssets_290" xlink:type="arc" order="0" />
    </link:definitionLink>
    <link:definitionLink xlink:type="extended" xlink:role="http://harrow.com/role/ScheduleOfEstimatedFutureAmortizationExpenseDetails" xlink:title="999058 - Disclosure - SCHEDULE OF ESTIMATED FUTURE AMORTIZATION EXPENSE (Details)" />
    <link:definitionLink xlink:type="extended" xlink:role="http://harrow.com/role/IntangibleAssetsAndGoodwillDetailsNarrative" xlink:title="999059 - Disclosure - INTANGIBLE ASSETS AND GOODWILL (Details Narrative)" />
    <link:definitionLink xlink:type="extended" xlink:role="http://harrow.com/role/ScheduleOfAccountsPayableAndAccruedExpensesDetails" xlink:title="999060 - Disclosure - SCHEDULE OF ACCOUNTS PAYABLE AND ACCRUED EXPENSES (Details)" />
    <link:definitionLink xlink:type="extended" xlink:role="http://harrow.com/role/ScheduleOfLongTermDebtDetails" xlink:title="999061 - Disclosure - SCHEDULE OF LONG TERM DEBT (Details)">
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShortTermDebtLineItems" xlink:label="loc_us-gaapShortTermDebtLineItems" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfShortTermDebtTable" xlink:label="loc_us-gaapScheduleOfShortTermDebtTable" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xbrldt:contextElement="segment" xlink:from="loc_us-gaapShortTermDebtLineItems" xlink:to="loc_us-gaapScheduleOfShortTermDebtTable" xlink:type="arc" order="10" xbrldt:closed="true" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentAxis" xlink:label="loc_us-gaapDebtInstrumentAxis" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaapScheduleOfShortTermDebtTable" xlink:to="loc_us-gaapDebtInstrumentAxis" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentNameDomain" xlink:label="loc_us-gaapDebtInstrumentNameDomain" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaapDebtInstrumentAxis" xlink:to="loc_us-gaapDebtInstrumentNameDomain" xlink:type="arc" order="20" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentNameDomain" xlink:label="loc_us-gaapDebtInstrumentNameDomain_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xbrldt:contextElement="segment" xlink:from="loc_us-gaapDebtInstrumentAxis" xlink:to="loc_us-gaapDebtInstrumentNameDomain_10" xlink:type="arc" order="30" />
      <link:loc xlink:type="locator" xlink:href="hrow-20250930.xsd#HROW_SeniorNotesDueAprilTwoThousandTwentySixMember" xlink:label="loc_HROWSeniorNotesDueAprilTwoThousandTwentySixMember_0" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapDebtInstrumentNameDomain" xlink:to="loc_HROWSeniorNotesDueAprilTwoThousandTwentySixMember_0" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="hrow-20250930.xsd#HROW_SeniorNotesDueDecemberTwoThousandTwentySevenMember" xlink:label="loc_HROWSeniorNotesDueDecemberTwoThousandTwentySevenMember_20" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapDebtInstrumentNameDomain" xlink:to="loc_HROWSeniorNotesDueDecemberTwoThousandTwentySevenMember_20" xlink:type="arc" order="21" />
      <link:loc xlink:type="locator" xlink:href="hrow-20250930.xsd#HROW_OaktreeLoanDueJanuaryTwoThousandTwentySixMember" xlink:label="loc_HROWOaktreeLoanDueJanuaryTwoThousandTwentySixMember_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapDebtInstrumentNameDomain" xlink:to="loc_HROWOaktreeLoanDueJanuaryTwoThousandTwentySixMember_40" xlink:type="arc" order="41" />
      <link:loc xlink:type="locator" xlink:href="hrow-20250930.xsd#HROW_SeniorNotesDueSeptemberTwoThousandThirtyMember" xlink:label="loc_HROWSeniorNotesDueSeptemberTwoThousandThirtyMember_60" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapDebtInstrumentNameDomain" xlink:to="loc_HROWSeniorNotesDueSeptemberTwoThousandThirtyMember_60" xlink:type="arc" order="61" />
      <link:loc xlink:type="locator" xlink:href="hrow-20250930.xsd#HROW_LongTermNotesPayableGross" xlink:label="loc_HROWLongTermNotesPayableGross_110" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShortTermDebtLineItems" xlink:to="loc_HROWLongTermNotesPayableGross_110" xlink:type="arc" order="0" />
      <link:loc xlink:type="locator" xlink:href="hrow-20250930.xsd#HROW_NotesPayableCurrentGross" xlink:label="loc_HROWNotesPayableCurrentGross_110" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShortTermDebtLineItems" xlink:to="loc_HROWNotesPayableCurrentGross_110" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentUnamortizedDiscountCurrent" xlink:label="loc_us-gaapDebtInstrumentUnamortizedDiscountCurrent_110" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShortTermDebtLineItems" xlink:to="loc_us-gaapDebtInstrumentUnamortizedDiscountCurrent_110" xlink:type="arc" order="2" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NotesPayableCurrent" xlink:label="loc_us-gaapNotesPayableCurrent_110" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShortTermDebtLineItems" xlink:to="loc_us-gaapNotesPayableCurrent_110" xlink:type="arc" order="3" />
    </link:definitionLink>
    <link:definitionLink xlink:type="extended" xlink:role="http://harrow.com/role/ScheduleOfLongTermDebtDetailsParenthetical" xlink:title="999062 - Disclosure - SCHEDULE OF LONG TERM DEBT (Details) (Parenthetical)">
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentLineItems" xlink:label="loc_us-gaapDebtInstrumentLineItems" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentTable" xlink:label="loc_us-gaapDebtInstrumentTable" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xbrldt:contextElement="segment" xlink:from="loc_us-gaapDebtInstrumentLineItems" xlink:to="loc_us-gaapDebtInstrumentTable" xlink:type="arc" order="10" xbrldt:closed="true" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeAxis" xlink:label="loc_us-gaapLongtermDebtTypeAxis" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaapDebtInstrumentTable" xlink:to="loc_us-gaapLongtermDebtTypeAxis" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeDomain" xlink:label="loc_us-gaapLongtermDebtTypeDomain" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaapLongtermDebtTypeAxis" xlink:to="loc_us-gaapLongtermDebtTypeDomain" xlink:type="arc" order="20" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeDomain" xlink:label="loc_us-gaapLongtermDebtTypeDomain_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xbrldt:contextElement="segment" xlink:from="loc_us-gaapLongtermDebtTypeAxis" xlink:to="loc_us-gaapLongtermDebtTypeDomain_10" xlink:type="arc" order="30" />
      <link:loc xlink:type="locator" xlink:href="hrow-20250930.xsd#HROW_SeniorNotesDueAprilTwoThousandTwentySixMember" xlink:label="loc_HROWSeniorNotesDueAprilTwoThousandTwentySixMember_0" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapLongtermDebtTypeDomain" xlink:to="loc_HROWSeniorNotesDueAprilTwoThousandTwentySixMember_0" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="hrow-20250930.xsd#HROW_SeniorNotesDueDecemberTwoThousandTwentySevenMember" xlink:label="loc_HROWSeniorNotesDueDecemberTwoThousandTwentySevenMember_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapLongtermDebtTypeDomain" xlink:to="loc_HROWSeniorNotesDueDecemberTwoThousandTwentySevenMember_10" xlink:type="arc" order="11" />
      <link:loc xlink:type="locator" xlink:href="hrow-20250930.xsd#HROW_SeniorNotesDueSeptemberTwoThousandThirtyMember" xlink:label="loc_HROWSeniorNotesDueSeptemberTwoThousandThirtyMember_30" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapLongtermDebtTypeDomain" xlink:to="loc_HROWSeniorNotesDueSeptemberTwoThousandThirtyMember_30" xlink:type="arc" order="31" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentAxis" xlink:label="loc_us-gaapDebtInstrumentAxis" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaapDebtInstrumentTable" xlink:to="loc_us-gaapDebtInstrumentAxis" xlink:type="arc" order="2" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentNameDomain" xlink:label="loc_us-gaapDebtInstrumentNameDomain" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaapDebtInstrumentAxis" xlink:to="loc_us-gaapDebtInstrumentNameDomain" xlink:type="arc" order="20" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentNameDomain" xlink:label="loc_us-gaapDebtInstrumentNameDomain_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xbrldt:contextElement="segment" xlink:from="loc_us-gaapDebtInstrumentAxis" xlink:to="loc_us-gaapDebtInstrumentNameDomain_10" xlink:type="arc" order="30" />
      <link:loc xlink:type="locator" xlink:href="hrow-20250930.xsd#HROW_OaktreeLoanDueJanuaryTwoThousandTwentySixMember" xlink:label="loc_HROWOaktreeLoanDueJanuaryTwoThousandTwentySixMember_20" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapDebtInstrumentNameDomain" xlink:to="loc_HROWOaktreeLoanDueJanuaryTwoThousandTwentySixMember_20" xlink:type="arc" order="21" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentMaturityDateDescription" xlink:label="loc_us-gaapDebtInstrumentMaturityDateDescription_50" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapDebtInstrumentLineItems" xlink:to="loc_us-gaapDebtInstrumentMaturityDateDescription_50" xlink:type="arc" order="0" />
    </link:definitionLink>
    <link:definitionLink xlink:type="extended" xlink:role="http://harrow.com/role/ScheduleOfFutureMinimumPaymentUnderNotesPayablesDetails" xlink:title="999063 - Disclosure - SCHEDULE OF FUTURE MINIMUM PAYMENT UNDER NOTES PAYABLES (Details)" />
    <link:definitionLink xlink:type="extended" xlink:role="http://harrow.com/role/DebtDetailsNarrative" xlink:title="999064 - Disclosure - DEBT (Details Narrative)">
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentLineItems" xlink:label="loc_us-gaapDebtInstrumentLineItems" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentTable" xlink:label="loc_us-gaapDebtInstrumentTable" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xbrldt:contextElement="segment" xlink:from="loc_us-gaapDebtInstrumentLineItems" xlink:to="loc_us-gaapDebtInstrumentTable" xlink:type="arc" order="10" xbrldt:closed="true" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentAxis" xlink:label="loc_us-gaapDebtInstrumentAxis" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaapDebtInstrumentTable" xlink:to="loc_us-gaapDebtInstrumentAxis" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentNameDomain" xlink:label="loc_us-gaapDebtInstrumentNameDomain" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaapDebtInstrumentAxis" xlink:to="loc_us-gaapDebtInstrumentNameDomain" xlink:type="arc" order="20" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentNameDomain" xlink:label="loc_us-gaapDebtInstrumentNameDomain_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xbrldt:contextElement="segment" xlink:from="loc_us-gaapDebtInstrumentAxis" xlink:to="loc_us-gaapDebtInstrumentNameDomain_10" xlink:type="arc" order="30" />
      <link:loc xlink:type="locator" xlink:href="hrow-20250930.xsd#HROW_FifthThirdRevolvingCreditFacilityMember" xlink:label="loc_HROWFifthThirdRevolvingCreditFacilityMember_0" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapDebtInstrumentNameDomain" xlink:to="loc_HROWFifthThirdRevolvingCreditFacilityMember_0" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="hrow-20250930.xsd#HROW_OaktreeLoanDueTwoThousandTwentySixMember" xlink:label="loc_HROWOaktreeLoanDueTwoThousandTwentySixMember_150" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapDebtInstrumentNameDomain" xlink:to="loc_HROWOaktreeLoanDueTwoThousandTwentySixMember_150" xlink:type="arc" order="151" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CreditFacilityAxis" xlink:label="loc_us-gaapCreditFacilityAxis" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaapDebtInstrumentTable" xlink:to="loc_us-gaapCreditFacilityAxis" xlink:type="arc" order="2" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CreditFacilityDomain" xlink:label="loc_us-gaapCreditFacilityDomain" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaapCreditFacilityAxis" xlink:to="loc_us-gaapCreditFacilityDomain" xlink:type="arc" order="20" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CreditFacilityDomain" xlink:label="loc_us-gaapCreditFacilityDomain_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xbrldt:contextElement="segment" xlink:from="loc_us-gaapCreditFacilityAxis" xlink:to="loc_us-gaapCreditFacilityDomain_10" xlink:type="arc" order="30" />
      <link:loc xlink:type="locator" xlink:href="hrow-20250930.xsd#HROW_SeniorSecuredRevolvingCreditFacilityMember" xlink:label="loc_HROWSeniorSecuredRevolvingCreditFacilityMember_0" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapCreditFacilityDomain" xlink:to="loc_HROWSeniorSecuredRevolvingCreditFacilityMember_0" xlink:type="arc" order="2" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevolvingCreditFacilityMember" xlink:label="loc_us-gaapRevolvingCreditFacilityMember_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapCreditFacilityDomain" xlink:to="loc_us-gaapRevolvingCreditFacilityMember_10" xlink:type="arc" order="12" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeAxis" xlink:label="loc_srtRangeAxis" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaapDebtInstrumentTable" xlink:to="loc_srtRangeAxis" xlink:type="arc" order="3" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember" xlink:label="loc_srtRangeMember" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srtRangeAxis" xlink:to="loc_srtRangeMember" xlink:type="arc" order="20" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember" xlink:label="loc_srtRangeMember_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xbrldt:contextElement="segment" xlink:from="loc_srtRangeAxis" xlink:to="loc_srtRangeMember_10" xlink:type="arc" order="30" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MinimumMember" xlink:label="loc_srtMinimumMember_30" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srtRangeMember" xlink:to="loc_srtMinimumMember_30" xlink:type="arc" order="32" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MaximumMember" xlink:label="loc_srtMaximumMember_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srtRangeMember" xlink:to="loc_srtMaximumMember_40" xlink:type="arc" order="42" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AwardTypeAxis" xlink:label="loc_us-gaapAwardTypeAxis" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaapDebtInstrumentTable" xlink:to="loc_us-gaapAwardTypeAxis" xlink:type="arc" order="4" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="loc_us-gaapShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaapAwardTypeAxis" xlink:to="loc_us-gaapShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:type="arc" order="20" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="loc_us-gaapShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xbrldt:contextElement="segment" xlink:from="loc_us-gaapAwardTypeAxis" xlink:to="loc_us-gaapShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_10" xlink:type="arc" order="30" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SecuredOvernightFinancingRateSofrMember" xlink:label="loc_us-gaapSecuredOvernightFinancingRateSofrMember_50" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:to="loc_us-gaapSecuredOvernightFinancingRateSofrMember_50" xlink:type="arc" order="53" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeAxis" xlink:label="loc_us-gaapLongtermDebtTypeAxis" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaapDebtInstrumentTable" xlink:to="loc_us-gaapLongtermDebtTypeAxis" xlink:type="arc" order="5" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeDomain" xlink:label="loc_us-gaapLongtermDebtTypeDomain" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaapLongtermDebtTypeAxis" xlink:to="loc_us-gaapLongtermDebtTypeDomain" xlink:type="arc" order="20" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeDomain" xlink:label="loc_us-gaapLongtermDebtTypeDomain_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xbrldt:contextElement="segment" xlink:from="loc_us-gaapLongtermDebtTypeAxis" xlink:to="loc_us-gaapLongtermDebtTypeDomain_10" xlink:type="arc" order="30" />
      <link:loc xlink:type="locator" xlink:href="hrow-20250930.xsd#HROW_SeniorNotesDueTwoThousandTwentyThirtyMember" xlink:label="loc_HROWSeniorNotesDueTwoThousandTwentyThirtyMember_80" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapLongtermDebtTypeDomain" xlink:to="loc_HROWSeniorNotesDueTwoThousandTwentyThirtyMember_80" xlink:type="arc" order="81" />
      <link:loc xlink:type="locator" xlink:href="hrow-20250930.xsd#HROW_OaktreeLoanMember" xlink:label="loc_HROWOaktreeLoanMember_180" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapLongtermDebtTypeDomain" xlink:to="loc_HROWOaktreeLoanMember_180" xlink:type="arc" order="181" />
      <link:loc xlink:type="locator" xlink:href="hrow-20250930.xsd#HROW_SeniorNotesDueTwoThousandTwentySixMember" xlink:label="loc_HROWSeniorNotesDueTwoThousandTwentySixMember_220" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapLongtermDebtTypeDomain" xlink:to="loc_HROWSeniorNotesDueTwoThousandTwentySixMember_220" xlink:type="arc" order="221" />
      <link:loc xlink:type="locator" xlink:href="hrow-20250930.xsd#HROW_SeniorNotesDueTwoThousandTwentySevenMember" xlink:label="loc_HROWSeniorNotesDueTwoThousandTwentySevenMember_310" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapLongtermDebtTypeDomain" xlink:to="loc_HROWSeniorNotesDueTwoThousandTwentySevenMember_310" xlink:type="arc" order="311" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TypeOfArrangementAxis" xlink:label="loc_us-gaapTypeOfArrangementAxis" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaapDebtInstrumentTable" xlink:to="loc_us-gaapTypeOfArrangementAxis" xlink:type="arc" order="6" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember" xlink:label="loc_us-gaapArrangementsAndNonarrangementTransactionsMember" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaapTypeOfArrangementAxis" xlink:to="loc_us-gaapArrangementsAndNonarrangementTransactionsMember" xlink:type="arc" order="20" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember" xlink:label="loc_us-gaapArrangementsAndNonarrangementTransactionsMember_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xbrldt:contextElement="segment" xlink:from="loc_us-gaapTypeOfArrangementAxis" xlink:to="loc_us-gaapArrangementsAndNonarrangementTransactionsMember_10" xlink:type="arc" order="30" />
      <link:loc xlink:type="locator" xlink:href="hrow-20250930.xsd#HROW_SecondAmendmentMember" xlink:label="loc_HROWSecondAmendmentMember_120" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapArrangementsAndNonarrangementTransactionsMember" xlink:to="loc_HROWSecondAmendmentMember_120" xlink:type="arc" order="121" />
      <link:loc xlink:type="locator" xlink:href="hrow-20250930.xsd#HROW_OaktreeLoanMember" xlink:label="loc_HROWOaktreeLoanMember_130" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapArrangementsAndNonarrangementTransactionsMember" xlink:to="loc_HROWOaktreeLoanMember_130" xlink:type="arc" order="131" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_LegalEntityAxis" xlink:label="loc_deiLegalEntityAxis" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaapDebtInstrumentTable" xlink:to="loc_deiLegalEntityAxis" xlink:type="arc" order="7" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityDomain" xlink:label="loc_deiEntityDomain" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_deiLegalEntityAxis" xlink:to="loc_deiEntityDomain" xlink:type="arc" order="20" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityDomain" xlink:label="loc_deiEntityDomain_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xbrldt:contextElement="segment" xlink:from="loc_deiLegalEntityAxis" xlink:to="loc_deiEntityDomain_10" xlink:type="arc" order="30" />
      <link:loc xlink:type="locator" xlink:href="hrow-20250930.xsd#HROW_OaktreeFundAdministrationLLCMember" xlink:label="loc_HROWOaktreeFundAdministrationLLCMember_130" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_deiEntityDomain" xlink:to="loc_HROWOaktreeFundAdministrationLLCMember_130" xlink:type="arc" order="132" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_TitleOfIndividualAxis" xlink:label="loc_srtTitleOfIndividualAxis" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaapDebtInstrumentTable" xlink:to="loc_srtTitleOfIndividualAxis" xlink:type="arc" order="8" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_TitleOfIndividualWithRelationshipToEntityDomain" xlink:label="loc_srtTitleOfIndividualWithRelationshipToEntityDomain" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srtTitleOfIndividualAxis" xlink:to="loc_srtTitleOfIndividualWithRelationshipToEntityDomain" xlink:type="arc" order="20" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_TitleOfIndividualWithRelationshipToEntityDomain" xlink:label="loc_srtTitleOfIndividualWithRelationshipToEntityDomain_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xbrldt:contextElement="segment" xlink:from="loc_srtTitleOfIndividualAxis" xlink:to="loc_srtTitleOfIndividualWithRelationshipToEntityDomain_10" xlink:type="arc" order="30" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InvestorMember" xlink:label="loc_us-gaapInvestorMember_240" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srtTitleOfIndividualWithRelationshipToEntityDomain" xlink:to="loc_us-gaapInvestorMember_240" xlink:type="arc" order="241" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentFaceAmount" xlink:label="loc_us-gaapDebtInstrumentFaceAmount_440" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapDebtInstrumentLineItems" xlink:to="loc_us-gaapDebtInstrumentFaceAmount_440" xlink:type="arc" order="0" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentMaturityDate" xlink:label="loc_us-gaapDebtInstrumentMaturityDate_440" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapDebtInstrumentLineItems" xlink:to="loc_us-gaapDebtInstrumentMaturityDate_440" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentBasisSpreadOnVariableRate1" xlink:label="loc_us-gaapDebtInstrumentBasisSpreadOnVariableRate1_440" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapDebtInstrumentLineItems" xlink:to="loc_us-gaapDebtInstrumentBasisSpreadOnVariableRate1_440" xlink:type="arc" order="2" />
      <link:loc xlink:type="locator" xlink:href="hrow-20250930.xsd#HROW_UnusedFeeRate" xlink:label="loc_HROWUnusedFeeRate_440" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapDebtInstrumentLineItems" xlink:to="loc_HROWUnusedFeeRate_440" xlink:type="arc" order="3" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DeferredCostsCurrentAndNoncurrent" xlink:label="loc_us-gaapDeferredCostsCurrentAndNoncurrent_440" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapDebtInstrumentLineItems" xlink:to="loc_us-gaapDeferredCostsCurrentAndNoncurrent_440" xlink:type="arc" order="4" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentInterestRateStatedPercentage" xlink:label="loc_us-gaapDebtInstrumentInterestRateStatedPercentage_440" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapDebtInstrumentLineItems" xlink:to="loc_us-gaapDebtInstrumentInterestRateStatedPercentage_440" xlink:type="arc" order="5" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ProceedsFromSecuredNotesPayable" xlink:label="loc_us-gaapProceedsFromSecuredNotesPayable_440" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapDebtInstrumentLineItems" xlink:to="loc_us-gaapProceedsFromSecuredNotesPayable_440" xlink:type="arc" order="6" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PaymentsForUnderwritingExpense" xlink:label="loc_us-gaapPaymentsForUnderwritingExpense_440" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapDebtInstrumentLineItems" xlink:to="loc_us-gaapPaymentsForUnderwritingExpense_440" xlink:type="arc" order="7" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PaymentsOfStockIssuanceCosts" xlink:label="loc_us-gaapPaymentsOfStockIssuanceCosts_440" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapDebtInstrumentLineItems" xlink:to="loc_us-gaapPaymentsOfStockIssuanceCosts_440" xlink:type="arc" order="8" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentRedemptionPricePercentage" xlink:label="loc_us-gaapDebtInstrumentRedemptionPricePercentage_440" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapDebtInstrumentLineItems" xlink:to="loc_us-gaapDebtInstrumentRedemptionPricePercentage_440" xlink:type="arc" order="9" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InterestExpenseOtherLongTermDebt" xlink:label="loc_us-gaapInterestExpenseOtherLongTermDebt_440" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapDebtInstrumentLineItems" xlink:to="loc_us-gaapInterestExpenseOtherLongTermDebt_440" xlink:type="arc" order="10" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AmortizationOfFinancingCostsAndDiscounts" xlink:label="loc_us-gaapAmortizationOfFinancingCostsAndDiscounts_440" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapDebtInstrumentLineItems" xlink:to="loc_us-gaapAmortizationOfFinancingCostsAndDiscounts_440" xlink:type="arc" order="11" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LineOfCreditFacilityUnusedCapacityCommitmentFeePercentage" xlink:label="loc_us-gaapLineOfCreditFacilityUnusedCapacityCommitmentFeePercentage_440" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapDebtInstrumentLineItems" xlink:to="loc_us-gaapLineOfCreditFacilityUnusedCapacityCommitmentFeePercentage_440" xlink:type="arc" order="12" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentFeeAmount" xlink:label="loc_us-gaapDebtInstrumentFeeAmount_440" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapDebtInstrumentLineItems" xlink:to="loc_us-gaapDebtInstrumentFeeAmount_440" xlink:type="arc" order="13" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RepaymentsOfDebt" xlink:label="loc_us-gaapRepaymentsOfDebt_440" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapDebtInstrumentLineItems" xlink:to="loc_us-gaapRepaymentsOfDebt_440" xlink:type="arc" order="14" />
      <link:loc xlink:type="locator" xlink:href="hrow-20250930.xsd#HROW_UnaccruedExitFee" xlink:label="loc_HROWUnaccruedExitFee_440" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapDebtInstrumentLineItems" xlink:to="loc_HROWUnaccruedExitFee_440" xlink:type="arc" order="15" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RedemptionPremium" xlink:label="loc_us-gaapRedemptionPremium_440" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapDebtInstrumentLineItems" xlink:to="loc_us-gaapRedemptionPremium_440" xlink:type="arc" order="16" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_WriteOffOfDeferredDebtIssuanceCost" xlink:label="loc_us-gaapWriteOffOfDeferredDebtIssuanceCost_440" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapDebtInstrumentLineItems" xlink:to="loc_us-gaapWriteOffOfDeferredDebtIssuanceCost_440" xlink:type="arc" order="17" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_GainsLossesOnExtinguishmentOfDebt" xlink:label="loc_us-gaapGainsLossesOnExtinguishmentOfDebt_440" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapDebtInstrumentLineItems" xlink:to="loc_us-gaapGainsLossesOnExtinguishmentOfDebt_440" xlink:type="arc" order="18" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentIncreaseDecreaseForPeriodNet" xlink:label="loc_us-gaapDebtInstrumentIncreaseDecreaseForPeriodNet_440" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapDebtInstrumentLineItems" xlink:to="loc_us-gaapDebtInstrumentIncreaseDecreaseForPeriodNet_440" xlink:type="arc" order="19" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InterestExpense" xlink:label="loc_us-gaapInterestExpense_440" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapDebtInstrumentLineItems" xlink:to="loc_us-gaapInterestExpense_440" xlink:type="arc" order="20" />
      <link:loc xlink:type="locator" xlink:href="hrow-20250930.xsd#HROW_UnaccruedInterest" xlink:label="loc_HROWUnaccruedInterest_440" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapDebtInstrumentLineItems" xlink:to="loc_HROWUnaccruedInterest_440" xlink:type="arc" order="21" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_UnamortizedDebtIssuanceExpense" xlink:label="loc_us-gaapUnamortizedDebtIssuanceExpense_440" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapDebtInstrumentLineItems" xlink:to="loc_us-gaapUnamortizedDebtIssuanceExpense_440" xlink:type="arc" order="22" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SharesIssuedPricePerShare" xlink:label="loc_us-gaapSharesIssuedPricePerShare_440" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapDebtInstrumentLineItems" xlink:to="loc_us-gaapSharesIssuedPricePerShare_440" xlink:type="arc" order="23" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentInterestRateDuringPeriod" xlink:label="loc_us-gaapDebtInstrumentInterestRateDuringPeriod_440" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapDebtInstrumentLineItems" xlink:to="loc_us-gaapDebtInstrumentInterestRateDuringPeriod_440" xlink:type="arc" order="25" />
    </link:definitionLink>
    <link:definitionLink xlink:type="extended" xlink:role="http://harrow.com/role/LeasesDetailsNarrative" xlink:title="999065 - Disclosure - LEASES (Details Narrative)">
      <link:loc xlink:type="locator" xlink:href="hrow-20250930.xsd#HROW_LeaseLineItems" xlink:label="loc_HROWLeaseLineItems" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LesseeLeaseDescriptionTable" xlink:label="loc_us-gaapLesseeLeaseDescriptionTable" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xbrldt:contextElement="segment" xlink:from="loc_HROWLeaseLineItems" xlink:to="loc_us-gaapLesseeLeaseDescriptionTable" xlink:type="arc" order="10" xbrldt:closed="true" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeAxis" xlink:label="loc_srtRangeAxis" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaapLesseeLeaseDescriptionTable" xlink:to="loc_srtRangeAxis" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember" xlink:label="loc_srtRangeMember" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srtRangeAxis" xlink:to="loc_srtRangeMember" xlink:type="arc" order="20" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember" xlink:label="loc_srtRangeMember_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xbrldt:contextElement="segment" xlink:from="loc_srtRangeAxis" xlink:to="loc_srtRangeMember_10" xlink:type="arc" order="30" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MinimumMember" xlink:label="loc_srtMinimumMember_0" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srtRangeMember" xlink:to="loc_srtMinimumMember_0" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MaximumMember" xlink:label="loc_srtMaximumMember_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srtRangeMember" xlink:to="loc_srtMaximumMember_10" xlink:type="arc" order="11" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PropertyPlantAndEquipmentByTypeAxis" xlink:label="loc_us-gaapPropertyPlantAndEquipmentByTypeAxis" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaapLesseeLeaseDescriptionTable" xlink:to="loc_us-gaapPropertyPlantAndEquipmentByTypeAxis" xlink:type="arc" order="2" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:label="loc_us-gaapPropertyPlantAndEquipmentTypeDomain" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaapPropertyPlantAndEquipmentByTypeAxis" xlink:to="loc_us-gaapPropertyPlantAndEquipmentTypeDomain" xlink:type="arc" order="20" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:label="loc_us-gaapPropertyPlantAndEquipmentTypeDomain_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xbrldt:contextElement="segment" xlink:from="loc_us-gaapPropertyPlantAndEquipmentByTypeAxis" xlink:to="loc_us-gaapPropertyPlantAndEquipmentTypeDomain_10" xlink:type="arc" order="30" />
      <link:loc xlink:type="locator" xlink:href="hrow-20250930.xsd#HROW_OfficeAndLaboratorySpaceMember" xlink:label="loc_HROWOfficeAndLaboratorySpaceMember_0" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapPropertyPlantAndEquipmentTypeDomain" xlink:to="loc_HROWOfficeAndLaboratorySpaceMember_0" xlink:type="arc" order="2" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_StatementGeographicalAxis" xlink:label="loc_srtStatementGeographicalAxis" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaapLesseeLeaseDescriptionTable" xlink:to="loc_srtStatementGeographicalAxis" xlink:type="arc" order="3" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_SegmentGeographicalDomain" xlink:label="loc_srtSegmentGeographicalDomain" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srtStatementGeographicalAxis" xlink:to="loc_srtSegmentGeographicalDomain" xlink:type="arc" order="20" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_SegmentGeographicalDomain" xlink:label="loc_srtSegmentGeographicalDomain_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xbrldt:contextElement="segment" xlink:from="loc_srtStatementGeographicalAxis" xlink:to="loc_srtSegmentGeographicalDomain_10" xlink:type="arc" order="30" />
      <link:loc xlink:type="locator" xlink:href="hrow-20250930.xsd#HROW_LedgewoodMember" xlink:label="loc_HROWLedgewoodMember_20" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srtSegmentGeographicalDomain" xlink:to="loc_HROWLedgewoodMember_20" xlink:type="arc" order="21" />
      <link:loc xlink:type="locator" xlink:href="hrow-20250930.xsd#HROW_NashvilleMember" xlink:label="loc_HROWNashvilleMember_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srtSegmentGeographicalDomain" xlink:to="loc_HROWNashvilleMember_40" xlink:type="arc" order="41" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeStatementLocationAxis" xlink:label="loc_us-gaapIncomeStatementLocationAxis" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaapLesseeLeaseDescriptionTable" xlink:to="loc_us-gaapIncomeStatementLocationAxis" xlink:type="arc" order="4" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeStatementLocationDomain" xlink:label="loc_us-gaapIncomeStatementLocationDomain" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaapIncomeStatementLocationAxis" xlink:to="loc_us-gaapIncomeStatementLocationDomain" xlink:type="arc" order="20" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeStatementLocationDomain" xlink:label="loc_us-gaapIncomeStatementLocationDomain_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xbrldt:contextElement="segment" xlink:from="loc_us-gaapIncomeStatementLocationAxis" xlink:to="loc_us-gaapIncomeStatementLocationDomain_10" xlink:type="arc" order="30" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SellingGeneralAndAdministrativeExpensesMember" xlink:label="loc_us-gaapSellingGeneralAndAdministrativeExpensesMember_130" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapIncomeStatementLocationDomain" xlink:to="loc_us-gaapSellingGeneralAndAdministrativeExpensesMember_130" xlink:type="arc" order="131" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LesseeOperatingLeaseRemainingLeaseTerm" xlink:label="loc_us-gaapLesseeOperatingLeaseRemainingLeaseTerm_180" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_HROWLeaseLineItems" xlink:to="loc_us-gaapLesseeOperatingLeaseRemainingLeaseTerm_180" xlink:type="arc" order="0" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AreaOfLand" xlink:label="loc_us-gaapAreaOfLand_180" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_HROWLeaseLineItems" xlink:to="loc_us-gaapAreaOfLand_180" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="hrow-20250930.xsd#HROW_LeaseExpirationDateDescription" xlink:label="loc_HROWLeaseExpirationDateDescription_180" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_HROWLeaseLineItems" xlink:to="loc_HROWLeaseExpirationDateDescription_180" xlink:type="arc" order="2" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OperatingLeaseWeightedAverageDiscountRatePercent" xlink:label="loc_us-gaapOperatingLeaseWeightedAverageDiscountRatePercent_180" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_HROWLeaseLineItems" xlink:to="loc_us-gaapOperatingLeaseWeightedAverageDiscountRatePercent_180" xlink:type="arc" order="3" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OperatingLeaseWeightedAverageRemainingLeaseTerm1" xlink:label="loc_us-gaapOperatingLeaseWeightedAverageRemainingLeaseTerm1_180" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_HROWLeaseLineItems" xlink:to="loc_us-gaapOperatingLeaseWeightedAverageRemainingLeaseTerm1_180" xlink:type="arc" order="4" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OperatingLeasePayments" xlink:label="loc_us-gaapOperatingLeasePayments_180" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_HROWLeaseLineItems" xlink:to="loc_us-gaapOperatingLeasePayments_180" xlink:type="arc" order="5" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OperatingLeaseExpense" xlink:label="loc_us-gaapOperatingLeaseExpense_180" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_HROWLeaseLineItems" xlink:to="loc_us-gaapOperatingLeaseExpense_180" xlink:type="arc" order="6" />
    </link:definitionLink>
    <link:definitionLink xlink:type="extended" xlink:role="http://harrow.com/role/ScheduleOfFutureLeasePaymentsUnderOperatingLeasesDetails" xlink:title="999066 - Disclosure - SCHEDULE OF FUTURE LEASE PAYMENTS UNDER OPERATING LEASES (Details)" />
    <link:definitionLink xlink:type="extended" xlink:role="http://harrow.com/role/ScheduleOfStockOptionPlanActivityDetails" xlink:title="999067 - Disclosure - SCHEDULE OF STOCK OPTION PLAN ACTIVITY (Details)">
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:label="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:label="loc_us-gaapScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xbrldt:contextElement="segment" xlink:from="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="loc_us-gaapScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:type="arc" order="10" xbrldt:closed="true" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AwardTypeAxis" xlink:label="loc_us-gaapAwardTypeAxis" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaapScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:to="loc_us-gaapAwardTypeAxis" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="loc_us-gaapShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaapAwardTypeAxis" xlink:to="loc_us-gaapShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:type="arc" order="20" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="loc_us-gaapShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xbrldt:contextElement="segment" xlink:from="loc_us-gaapAwardTypeAxis" xlink:to="loc_us-gaapShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_10" xlink:type="arc" order="30" />
      <link:loc xlink:type="locator" xlink:href="hrow-20250930.xsd#HROW_StockOptionPlanOneMember" xlink:label="loc_HROWStockOptionPlanOneMember_0" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:to="loc_HROWStockOptionPlanOneMember_0" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber" xlink:label="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber_40" xlink:type="arc" order="0" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice" xlink:label="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice_40" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross" xlink:label="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross_40" xlink:type="arc" order="2" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice" xlink:label="loc_us-gaapShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="loc_us-gaapShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice_40" xlink:type="arc" order="3" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised" xlink:label="loc_us-gaapStockIssuedDuringPeriodSharesStockOptionsExercised_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="loc_us-gaapStockIssuedDuringPeriodSharesStockOptionsExercised_40" xlink:type="arc" order="4" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice" xlink:label="loc_us-gaapShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="loc_us-gaapShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice_40" xlink:type="arc" order="5" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod" xlink:label="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod_40" xlink:type="arc" order="6" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsForfeituresInPeriodWeightedAverageExercisePrice" xlink:label="loc_us-gaapShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsForfeituresInPeriodWeightedAverageExercisePrice_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="loc_us-gaapShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsForfeituresInPeriodWeightedAverageExercisePrice_40" xlink:type="arc" order="7" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2" xlink:label="loc_us-gaapSharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="loc_us-gaapSharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2_40" xlink:type="arc" order="10" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue" xlink:label="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue_40" xlink:type="arc" order="11" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber" xlink:label="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber_40" xlink:type="arc" order="12" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableWeightedAverageExercisePrice" xlink:label="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableWeightedAverageExercisePrice_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableWeightedAverageExercisePrice_40" xlink:type="arc" order="13" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableWeightedAverageRemainingContractualTerm1" xlink:label="loc_us-gaapSharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableWeightedAverageRemainingContractualTerm1_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="loc_us-gaapSharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableWeightedAverageRemainingContractualTerm1_40" xlink:type="arc" order="14" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableIntrinsicValue1" xlink:label="loc_us-gaapSharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableIntrinsicValue1_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="loc_us-gaapSharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableIntrinsicValue1_40" xlink:type="arc" order="15" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingNumber" xlink:label="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingNumber_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingNumber_40" xlink:type="arc" order="16" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingWeightedAverageExercisePrice" xlink:label="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingWeightedAverageExercisePrice_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingWeightedAverageExercisePrice_40" xlink:type="arc" order="17" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingWeightedAverageRemainingContractualTerm1" xlink:label="loc_us-gaapSharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingWeightedAverageRemainingContractualTerm1_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="loc_us-gaapSharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingWeightedAverageRemainingContractualTerm1_40" xlink:type="arc" order="18" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingAggregateIntrinsicValue" xlink:label="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingAggregateIntrinsicValue_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingAggregateIntrinsicValue_40" xlink:type="arc" order="19" />
    </link:definitionLink>
    <link:definitionLink xlink:type="extended" xlink:role="http://harrow.com/role/ScheduleOfFairValueAssumptionsDetails" xlink:title="999068 - Disclosure - SCHEDULE OF FAIR VALUE ASSUMPTIONS (Details)">
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:label="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:label="loc_us-gaapScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xbrldt:contextElement="segment" xlink:from="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="loc_us-gaapScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:type="arc" order="10" xbrldt:closed="true" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AwardTypeAxis" xlink:label="loc_us-gaapAwardTypeAxis" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaapScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:to="loc_us-gaapAwardTypeAxis" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="loc_us-gaapShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaapAwardTypeAxis" xlink:to="loc_us-gaapShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:type="arc" order="20" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="loc_us-gaapShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xbrldt:contextElement="segment" xlink:from="loc_us-gaapAwardTypeAxis" xlink:to="loc_us-gaapShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_10" xlink:type="arc" order="30" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EmployeeStockOptionMember" xlink:label="loc_us-gaapEmployeeStockOptionMember_0" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:to="loc_us-gaapEmployeeStockOptionMember_0" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeAxis" xlink:label="loc_srtRangeAxis" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaapScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:to="loc_srtRangeAxis" xlink:type="arc" order="2" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember" xlink:label="loc_srtRangeMember" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srtRangeAxis" xlink:to="loc_srtRangeMember" xlink:type="arc" order="20" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember" xlink:label="loc_srtRangeMember_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xbrldt:contextElement="segment" xlink:from="loc_srtRangeAxis" xlink:to="loc_srtRangeMember_10" xlink:type="arc" order="30" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MinimumMember" xlink:label="loc_srtMinimumMember_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srtRangeMember" xlink:to="loc_srtMinimumMember_10" xlink:type="arc" order="12" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MaximumMember" xlink:label="loc_srtMaximumMember_20" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srtRangeMember" xlink:to="loc_srtMaximumMember_20" xlink:type="arc" order="22" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue" xlink:label="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_40" xlink:type="arc" order="0" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1" xlink:label="loc_us-gaapSharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="loc_us-gaapSharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1_40" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate" xlink:label="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate_40" xlink:type="arc" order="2" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate" xlink:label="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate_40" xlink:type="arc" order="3" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate" xlink:label="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate_40" xlink:type="arc" order="4" />
    </link:definitionLink>
    <link:definitionLink xlink:type="extended" xlink:role="http://harrow.com/role/ScheduleOfStockOptionOutstandingAndExercisableDetails" xlink:title="999069 - Disclosure - SCHEDULE OF STOCK OPTION OUTSTANDING AND EXERCISABLE (Details)">
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLineItems" xlink:label="loc_us-gaapShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLineItems" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeTable" xlink:label="loc_us-gaapScheduleOfShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeTable" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xbrldt:contextElement="segment" xlink:from="loc_us-gaapShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLineItems" xlink:to="loc_us-gaapScheduleOfShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeTable" xlink:type="arc" order="10" xbrldt:closed="true" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeAxis" xlink:label="loc_us-gaapShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeAxis" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaapScheduleOfShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeTable" xlink:to="loc_us-gaapShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeAxis" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeDomain" xlink:label="loc_us-gaapShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeDomain" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaapShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeAxis" xlink:to="loc_us-gaapShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeDomain" xlink:type="arc" order="20" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeDomain" xlink:label="loc_us-gaapShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeDomain_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xbrldt:contextElement="segment" xlink:from="loc_us-gaapShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeAxis" xlink:to="loc_us-gaapShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeDomain_10" xlink:type="arc" order="30" />
      <link:loc xlink:type="locator" xlink:href="hrow-20250930.xsd#HROW_RangeOneMember" xlink:label="loc_HROWRangeOneMember_0" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeDomain" xlink:to="loc_HROWRangeOneMember_0" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="hrow-20250930.xsd#HROW_RangeTwoMember" xlink:label="loc_HROWRangeTwoMember_20" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeDomain" xlink:to="loc_HROWRangeTwoMember_20" xlink:type="arc" order="21" />
      <link:loc xlink:type="locator" xlink:href="hrow-20250930.xsd#HROW_RangeThreeMember" xlink:label="loc_HROWRangeThreeMember_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeDomain" xlink:to="loc_HROWRangeThreeMember_40" xlink:type="arc" order="41" />
      <link:loc xlink:type="locator" xlink:href="hrow-20250930.xsd#HROW_RangeFourMember" xlink:label="loc_HROWRangeFourMember_60" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeDomain" xlink:to="loc_HROWRangeFourMember_60" xlink:type="arc" order="61" />
      <link:loc xlink:type="locator" xlink:href="hrow-20250930.xsd#HROW_RangeFiveMember" xlink:label="loc_HROWRangeFiveMember_80" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeDomain" xlink:to="loc_HROWRangeFiveMember_80" xlink:type="arc" order="81" />
      <link:loc xlink:type="locator" xlink:href="hrow-20250930.xsd#HROW_RangeSixMember" xlink:label="loc_HROWRangeSixMember_100" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeDomain" xlink:to="loc_HROWRangeSixMember_100" xlink:type="arc" order="101" />
      <link:loc xlink:type="locator" xlink:href="hrow-20250930.xsd#HROW_RangeSevenMember" xlink:label="loc_HROWRangeSevenMember_120" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeDomain" xlink:to="loc_HROWRangeSevenMember_120" xlink:type="arc" order="121" />
      <link:loc xlink:type="locator" xlink:href="hrow-20250930.xsd#HROW_RangeEightMember" xlink:label="loc_HROWRangeEightMember_140" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeDomain" xlink:to="loc_HROWRangeEightMember_140" xlink:type="arc" order="141" />
      <link:loc xlink:type="locator" xlink:href="hrow-20250930.xsd#HROW_RangeNineMember" xlink:label="loc_HROWRangeNineMember_160" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeDomain" xlink:to="loc_HROWRangeNineMember_160" xlink:type="arc" order="161" />
      <link:loc xlink:type="locator" xlink:href="hrow-20250930.xsd#HROW_RangeTenMember" xlink:label="loc_HROWRangeTenMember_180" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeDomain" xlink:to="loc_HROWRangeTenMember_180" xlink:type="arc" order="181" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLowerRangeLimit" xlink:label="loc_us-gaapShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLowerRangeLimit_230" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLineItems" xlink:to="loc_us-gaapShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLowerRangeLimit_230" xlink:type="arc" order="0" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeUpperRangeLimit" xlink:label="loc_us-gaapShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeUpperRangeLimit_230" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLineItems" xlink:to="loc_us-gaapShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeUpperRangeLimit_230" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeNumberOfOutstandingOptions" xlink:label="loc_us-gaapShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeNumberOfOutstandingOptions_230" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLineItems" xlink:to="loc_us-gaapShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeNumberOfOutstandingOptions_230" xlink:type="arc" order="2" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SharebasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeOutstandingOptionsWeightedAverageRemainingContractualTerm2" xlink:label="loc_us-gaapSharebasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeOutstandingOptionsWeightedAverageRemainingContractualTerm2_230" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLineItems" xlink:to="loc_us-gaapSharebasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeOutstandingOptionsWeightedAverageRemainingContractualTerm2_230" xlink:type="arc" order="3" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SharebasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeOutstandingOptionsWeightedAverageExercisePriceBeginningBalance1" xlink:label="loc_us-gaapSharebasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeOutstandingOptionsWeightedAverageExercisePriceBeginningBalance1_230" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLineItems" xlink:to="loc_us-gaapSharebasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeOutstandingOptionsWeightedAverageExercisePriceBeginningBalance1_230" xlink:type="arc" order="4" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeNumberOfExercisableOptions" xlink:label="loc_us-gaapShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeNumberOfExercisableOptions_230" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLineItems" xlink:to="loc_us-gaapShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeNumberOfExercisableOptions_230" xlink:type="arc" order="5" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SharebasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeExercisableOptionsWeightedAverageExercisePrice1" xlink:label="loc_us-gaapSharebasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeExercisableOptionsWeightedAverageExercisePrice1_230" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLineItems" xlink:to="loc_us-gaapSharebasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeExercisableOptionsWeightedAverageExercisePrice1_230" xlink:type="arc" order="6" />
    </link:definitionLink>
    <link:definitionLink xlink:type="extended" xlink:role="http://harrow.com/role/ScheduleOfRestrictedStockUnitsActivityDetails" xlink:title="999070 - Disclosure - SCHEDULE OF RESTRICTED STOCK UNITS ACTIVITY (Details)">
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:label="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:label="loc_us-gaapScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xbrldt:contextElement="segment" xlink:from="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="loc_us-gaapScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:type="arc" order="10" xbrldt:closed="true" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AwardTypeAxis" xlink:label="loc_us-gaapAwardTypeAxis" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaapScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:to="loc_us-gaapAwardTypeAxis" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="loc_us-gaapShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaapAwardTypeAxis" xlink:to="loc_us-gaapShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:type="arc" order="20" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="loc_us-gaapShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xbrldt:contextElement="segment" xlink:from="loc_us-gaapAwardTypeAxis" xlink:to="loc_us-gaapShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_10" xlink:type="arc" order="30" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestrictedStockUnitsRSUMember" xlink:label="loc_us-gaapRestrictedStockUnitsRSUMember_0" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:to="loc_us-gaapRestrictedStockUnitsRSUMember_0" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber" xlink:label="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_40" xlink:type="arc" order="0" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue" xlink:label="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_40" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod" xlink:label="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_40" xlink:type="arc" order="2" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue" xlink:label="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_40" xlink:type="arc" order="3" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod" xlink:label="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_40" xlink:type="arc" order="4" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue" xlink:label="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue_40" xlink:type="arc" order="5" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod" xlink:label="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod_40" xlink:type="arc" order="6" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue" xlink:label="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue_40" xlink:type="arc" order="7" />
    </link:definitionLink>
    <link:definitionLink xlink:type="extended" xlink:role="http://harrow.com/role/ScheduleOfPerformanceStockUnitsDetails" xlink:title="999071 - Disclosure - SCHEDULE OF PERFORMANCE STOCK UNITS (Details)">
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:label="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:label="loc_us-gaapScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xbrldt:contextElement="segment" xlink:from="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="loc_us-gaapScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:type="arc" order="10" xbrldt:closed="true" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_VestingAxis" xlink:label="loc_us-gaapVestingAxis" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaapScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:to="loc_us-gaapVestingAxis" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_VestingDomain" xlink:label="loc_us-gaapVestingDomain" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaapVestingAxis" xlink:to="loc_us-gaapVestingDomain" xlink:type="arc" order="20" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_VestingDomain" xlink:label="loc_us-gaapVestingDomain_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xbrldt:contextElement="segment" xlink:from="loc_us-gaapVestingAxis" xlink:to="loc_us-gaapVestingDomain_10" xlink:type="arc" order="30" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationAwardTrancheOneMember" xlink:label="loc_us-gaapShareBasedCompensationAwardTrancheOneMember_0" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapVestingDomain" xlink:to="loc_us-gaapShareBasedCompensationAwardTrancheOneMember_0" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationAwardTrancheTwoMember" xlink:label="loc_us-gaapShareBasedCompensationAwardTrancheTwoMember_20" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapVestingDomain" xlink:to="loc_us-gaapShareBasedCompensationAwardTrancheTwoMember_20" xlink:type="arc" order="21" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationAwardTrancheThreeMember" xlink:label="loc_us-gaapShareBasedCompensationAwardTrancheThreeMember_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapVestingDomain" xlink:to="loc_us-gaapShareBasedCompensationAwardTrancheThreeMember_40" xlink:type="arc" order="41" />
      <link:loc xlink:type="locator" xlink:href="hrow-20250930.xsd#HROW_ShareBasedCompensationAwardTrancheFourMember" xlink:label="loc_HROWShareBasedCompensationAwardTrancheFourMember_60" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapVestingDomain" xlink:to="loc_HROWShareBasedCompensationAwardTrancheFourMember_60" xlink:type="arc" order="61" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SharePrice" xlink:label="loc_us-gaapSharePrice_90" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="loc_us-gaapSharePrice_90" xlink:type="arc" order="0" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAcceleratedVestingNumber" xlink:label="loc_us-gaapSharebasedCompensationArrangementBySharebasedPaymentAwardAcceleratedVestingNumber_90" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="loc_us-gaapSharebasedCompensationArrangementBySharebasedPaymentAwardAcceleratedVestingNumber_90" xlink:type="arc" order="1" />
    </link:definitionLink>
    <link:definitionLink xlink:type="extended" xlink:role="http://harrow.com/role/ScheduleOfPerformanceStockUnitsActivityDetails" xlink:title="999072 - Disclosure - SCHEDULE OF PERFORMANCE STOCK UNITS ACTIVITY (Details)">
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:label="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:label="loc_us-gaapScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xbrldt:contextElement="segment" xlink:from="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="loc_us-gaapScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:type="arc" order="10" xbrldt:closed="true" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AwardTypeAxis" xlink:label="loc_us-gaapAwardTypeAxis" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaapScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:to="loc_us-gaapAwardTypeAxis" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="loc_us-gaapShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaapAwardTypeAxis" xlink:to="loc_us-gaapShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:type="arc" order="20" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="loc_us-gaapShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xbrldt:contextElement="segment" xlink:from="loc_us-gaapAwardTypeAxis" xlink:to="loc_us-gaapShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_10" xlink:type="arc" order="30" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PerformanceSharesMember" xlink:label="loc_us-gaapPerformanceSharesMember_0" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:to="loc_us-gaapPerformanceSharesMember_0" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber" xlink:label="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_40" xlink:type="arc" order="0" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue" xlink:label="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_40" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod" xlink:label="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_40" xlink:type="arc" order="2" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue" xlink:label="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_40" xlink:type="arc" order="3" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod" xlink:label="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_40" xlink:type="arc" order="4" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue" xlink:label="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue_40" xlink:type="arc" order="5" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod" xlink:label="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod_40" xlink:type="arc" order="6" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue" xlink:label="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue_40" xlink:type="arc" order="7" />
    </link:definitionLink>
    <link:definitionLink xlink:type="extended" xlink:role="http://harrow.com/role/ScheduleOfStockBasedCompensationGrantedToEmployeesDirectorsAndConsultantsDetails" xlink:title="999073 - Disclosure - SCHEDULE OF STOCK BASED COMPENSATION GRANTED TO EMPLOYEES, DIRECTORS AND CONSULTANTS (Details)">
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:label="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:label="loc_us-gaapScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xbrldt:contextElement="segment" xlink:from="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="loc_us-gaapScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:type="arc" order="10" xbrldt:closed="true" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_TitleOfIndividualAxis" xlink:label="loc_srtTitleOfIndividualAxis" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaapScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:to="loc_srtTitleOfIndividualAxis" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_TitleOfIndividualWithRelationshipToEntityDomain" xlink:label="loc_srtTitleOfIndividualWithRelationshipToEntityDomain" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srtTitleOfIndividualAxis" xlink:to="loc_srtTitleOfIndividualWithRelationshipToEntityDomain" xlink:type="arc" order="20" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_TitleOfIndividualWithRelationshipToEntityDomain" xlink:label="loc_srtTitleOfIndividualWithRelationshipToEntityDomain_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xbrldt:contextElement="segment" xlink:from="loc_srtTitleOfIndividualAxis" xlink:to="loc_srtTitleOfIndividualWithRelationshipToEntityDomain_10" xlink:type="arc" order="30" />
      <link:loc xlink:type="locator" xlink:href="hrow-20250930.xsd#HROW_EmployeesMember" xlink:label="loc_HROWEmployeesMember_0" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srtTitleOfIndividualWithRelationshipToEntityDomain" xlink:to="loc_HROWEmployeesMember_0" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_DirectorMember" xlink:label="loc_srtDirectorMember_80" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srtTitleOfIndividualWithRelationshipToEntityDomain" xlink:to="loc_srtDirectorMember_80" xlink:type="arc" order="81" />
      <link:loc xlink:type="locator" xlink:href="hrow-20250930.xsd#HROW_ConsultantsMember" xlink:label="loc_HROWConsultantsMember_120" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srtTitleOfIndividualWithRelationshipToEntityDomain" xlink:to="loc_HROWConsultantsMember_120" xlink:type="arc" order="121" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeStatementLocationAxis" xlink:label="loc_us-gaapIncomeStatementLocationAxis" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaapScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:to="loc_us-gaapIncomeStatementLocationAxis" xlink:type="arc" order="2" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeStatementLocationDomain" xlink:label="loc_us-gaapIncomeStatementLocationDomain" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaapIncomeStatementLocationAxis" xlink:to="loc_us-gaapIncomeStatementLocationDomain" xlink:type="arc" order="20" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeStatementLocationDomain" xlink:label="loc_us-gaapIncomeStatementLocationDomain_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xbrldt:contextElement="segment" xlink:from="loc_us-gaapIncomeStatementLocationAxis" xlink:to="loc_us-gaapIncomeStatementLocationDomain_10" xlink:type="arc" order="30" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SellingGeneralAndAdministrativeExpensesMember" xlink:label="loc_us-gaapSellingGeneralAndAdministrativeExpensesMember_0" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapIncomeStatementLocationDomain" xlink:to="loc_us-gaapSellingGeneralAndAdministrativeExpensesMember_0" xlink:type="arc" order="2" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ResearchAndDevelopmentExpenseMember" xlink:label="loc_us-gaapResearchAndDevelopmentExpenseMember_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapIncomeStatementLocationDomain" xlink:to="loc_us-gaapResearchAndDevelopmentExpenseMember_40" xlink:type="arc" order="42" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AllocatedShareBasedCompensationExpense" xlink:label="loc_us-gaapAllocatedShareBasedCompensationExpense_210" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="loc_us-gaapAllocatedShareBasedCompensationExpense_210" xlink:type="arc" order="0" />
    </link:definitionLink>
    <link:definitionLink xlink:type="extended" xlink:role="http://harrow.com/role/StockholdersEquityAndStock-basedCompensationDetailsNarrative" xlink:title="999074 - Disclosure - STOCKHOLDERS&#8217; EQUITY AND STOCK-BASED COMPENSATION (Details Narrative)">
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems" xlink:label="loc_us-gaapAccumulatedOtherComprehensiveIncomeLossLineItems" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossTable" xlink:label="loc_us-gaapAccumulatedOtherComprehensiveIncomeLossTable" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xbrldt:contextElement="segment" xlink:from="loc_us-gaapAccumulatedOtherComprehensiveIncomeLossLineItems" xlink:to="loc_us-gaapAccumulatedOtherComprehensiveIncomeLossTable" xlink:type="arc" order="10" xbrldt:closed="true" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RelatedPartyTransactionsByRelatedPartyAxis" xlink:label="loc_us-gaapRelatedPartyTransactionsByRelatedPartyAxis" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaapAccumulatedOtherComprehensiveIncomeLossTable" xlink:to="loc_us-gaapRelatedPartyTransactionsByRelatedPartyAxis" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RelatedPartyDomain" xlink:label="loc_us-gaapRelatedPartyDomain" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaapRelatedPartyTransactionsByRelatedPartyAxis" xlink:to="loc_us-gaapRelatedPartyDomain" xlink:type="arc" order="20" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RelatedPartyDomain" xlink:label="loc_us-gaapRelatedPartyDomain_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xbrldt:contextElement="segment" xlink:from="loc_us-gaapRelatedPartyTransactionsByRelatedPartyAxis" xlink:to="loc_us-gaapRelatedPartyDomain_10" xlink:type="arc" order="30" />
      <link:loc xlink:type="locator" xlink:href="hrow-20250930.xsd#HROW_AndrewRBollMember" xlink:label="loc_HROWAndrewRBollMember_0" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapRelatedPartyDomain" xlink:to="loc_HROWAndrewRBollMember_0" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="hrow-20250930.xsd#HROW_MarkLBaumMember" xlink:label="loc_HROWMarkLBaumMember_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapRelatedPartyDomain" xlink:to="loc_HROWMarkLBaumMember_10" xlink:type="arc" order="11" />
      <link:loc xlink:type="locator" xlink:href="hrow-20250930.xsd#HROW_JohnPSaharekMember" xlink:label="loc_HROWJohnPSaharekMember_20" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapRelatedPartyDomain" xlink:to="loc_HROWJohnPSaharekMember_20" xlink:type="arc" order="21" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementEquityComponentsAxis" xlink:label="loc_us-gaapStatementEquityComponentsAxis" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaapAccumulatedOtherComprehensiveIncomeLossTable" xlink:to="loc_us-gaapStatementEquityComponentsAxis" xlink:type="arc" order="2" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityComponentDomain" xlink:label="loc_us-gaapEquityComponentDomain" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaapStatementEquityComponentsAxis" xlink:to="loc_us-gaapEquityComponentDomain" xlink:type="arc" order="20" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityComponentDomain" xlink:label="loc_us-gaapEquityComponentDomain_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xbrldt:contextElement="segment" xlink:from="loc_us-gaapStatementEquityComponentsAxis" xlink:to="loc_us-gaapEquityComponentDomain_10" xlink:type="arc" order="30" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockMember" xlink:label="loc_us-gaapCommonStockMember_0" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapEquityComponentDomain" xlink:to="loc_us-gaapCommonStockMember_0" xlink:type="arc" order="2" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AwardTypeAxis" xlink:label="loc_us-gaapAwardTypeAxis" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaapAccumulatedOtherComprehensiveIncomeLossTable" xlink:to="loc_us-gaapAwardTypeAxis" xlink:type="arc" order="3" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="loc_us-gaapShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaapAwardTypeAxis" xlink:to="loc_us-gaapShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:type="arc" order="20" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="loc_us-gaapShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xbrldt:contextElement="segment" xlink:from="loc_us-gaapAwardTypeAxis" xlink:to="loc_us-gaapShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_10" xlink:type="arc" order="30" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PerformanceSharesMember" xlink:label="loc_us-gaapPerformanceSharesMember_0" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:to="loc_us-gaapPerformanceSharesMember_0" xlink:type="arc" order="3" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EmployeeStockOptionMember" xlink:label="loc_us-gaapEmployeeStockOptionMember_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:to="loc_us-gaapEmployeeStockOptionMember_40" xlink:type="arc" order="42" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestrictedStockUnitsRSUMember" xlink:label="loc_us-gaapRestrictedStockUnitsRSUMember_60" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:to="loc_us-gaapRestrictedStockUnitsRSUMember_60" xlink:type="arc" order="62" />
      <link:loc xlink:type="locator" xlink:href="hrow-20250930.xsd#HROW_RSUAndPSUMember" xlink:label="loc_HROWRSUAndPSUMember_70" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:to="loc_HROWRSUAndPSUMember_70" xlink:type="arc" order="72" />
      <link:loc xlink:type="locator" xlink:href="hrow-20250930.xsd#HROW_PerformanceStockUnitsPSUMember" xlink:label="loc_HROWPerformanceStockUnitsPSUMember_250" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:to="loc_HROWPerformanceStockUnitsPSUMember_250" xlink:type="arc" order="252" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AwardDateAxis" xlink:label="loc_us-gaapAwardDateAxis" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaapAccumulatedOtherComprehensiveIncomeLossTable" xlink:to="loc_us-gaapAwardDateAxis" xlink:type="arc" order="4" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AwardDateDomain" xlink:label="loc_us-gaapAwardDateDomain" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaapAwardDateAxis" xlink:to="loc_us-gaapAwardDateDomain" xlink:type="arc" order="20" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AwardDateDomain" xlink:label="loc_us-gaapAwardDateDomain_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xbrldt:contextElement="segment" xlink:from="loc_us-gaapAwardDateAxis" xlink:to="loc_us-gaapAwardDateDomain_10" xlink:type="arc" order="30" />
      <link:loc xlink:type="locator" xlink:href="hrow-20250930.xsd#HROW_AprilTwentyTwentyThreeMember" xlink:label="loc_HROWAprilTwentyTwentyThreeMember_0" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapAwardDateDomain" xlink:to="loc_HROWAprilTwentyTwentyThreeMember_0" xlink:type="arc" order="4" />
      <link:loc xlink:type="locator" xlink:href="hrow-20250930.xsd#HROW_PriorPeriodsMember" xlink:label="loc_HROWPriorPeriodsMember_60" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapAwardDateDomain" xlink:to="loc_HROWPriorPeriodsMember_60" xlink:type="arc" order="63" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_TitleOfIndividualAxis" xlink:label="loc_srtTitleOfIndividualAxis" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaapAccumulatedOtherComprehensiveIncomeLossTable" xlink:to="loc_srtTitleOfIndividualAxis" xlink:type="arc" order="5" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_TitleOfIndividualWithRelationshipToEntityDomain" xlink:label="loc_srtTitleOfIndividualWithRelationshipToEntityDomain" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srtTitleOfIndividualAxis" xlink:to="loc_srtTitleOfIndividualWithRelationshipToEntityDomain" xlink:type="arc" order="20" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_TitleOfIndividualWithRelationshipToEntityDomain" xlink:label="loc_srtTitleOfIndividualWithRelationshipToEntityDomain_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xbrldt:contextElement="segment" xlink:from="loc_srtTitleOfIndividualAxis" xlink:to="loc_srtTitleOfIndividualWithRelationshipToEntityDomain_10" xlink:type="arc" order="30" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_DirectorMember" xlink:label="loc_srtDirectorMember_100" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srtTitleOfIndividualWithRelationshipToEntityDomain" xlink:to="loc_srtDirectorMember_100" xlink:type="arc" order="101" />
      <link:loc xlink:type="locator" xlink:href="hrow-20250930.xsd#HROW_EmployeesAndConsultantMember" xlink:label="loc_HROWEmployeesAndConsultantMember_140" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srtTitleOfIndividualWithRelationshipToEntityDomain" xlink:to="loc_HROWEmployeesAndConsultantMember_140" xlink:type="arc" order="142" />
      <link:loc xlink:type="locator" xlink:href="hrow-20250930.xsd#HROW_EmployeesAndDirectorsMember" xlink:label="loc_HROWEmployeesAndDirectorsMember_150" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srtTitleOfIndividualWithRelationshipToEntityDomain" xlink:to="loc_HROWEmployeesAndDirectorsMember_150" xlink:type="arc" order="151" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ChiefExecutiveOfficerMember" xlink:label="loc_srtChiefExecutiveOfficerMember_250" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srtTitleOfIndividualWithRelationshipToEntityDomain" xlink:to="loc_srtChiefExecutiveOfficerMember_250" xlink:type="arc" order="251" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeAxis" xlink:label="loc_srtRangeAxis" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaapAccumulatedOtherComprehensiveIncomeLossTable" xlink:to="loc_srtRangeAxis" xlink:type="arc" order="6" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember" xlink:label="loc_srtRangeMember" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srtRangeAxis" xlink:to="loc_srtRangeMember" xlink:type="arc" order="20" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember" xlink:label="loc_srtRangeMember_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xbrldt:contextElement="segment" xlink:from="loc_srtRangeAxis" xlink:to="loc_srtRangeMember_10" xlink:type="arc" order="30" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MinimumMember" xlink:label="loc_srtMinimumMember_260" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srtRangeMember" xlink:to="loc_srtMinimumMember_260" xlink:type="arc" order="262" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MaximumMember" xlink:label="loc_srtMaximumMember_270" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srtRangeMember" xlink:to="loc_srtMaximumMember_270" xlink:type="arc" order="272" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod" xlink:label="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_350" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapAccumulatedOtherComprehensiveIncomeLossLineItems" xlink:to="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_350" xlink:type="arc" order="0" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockIssuedDuringPeriodSharesNewIssues" xlink:label="loc_us-gaapStockIssuedDuringPeriodSharesNewIssues_350" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapAccumulatedOtherComprehensiveIncomeLossLineItems" xlink:to="loc_us-gaapStockIssuedDuringPeriodSharesNewIssues_350" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SharesPaidForTaxWithholdingForShareBasedCompensation" xlink:label="loc_us-gaapSharesPaidForTaxWithholdingForShareBasedCompensation_350" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapAccumulatedOtherComprehensiveIncomeLossLineItems" xlink:to="loc_us-gaapSharesPaidForTaxWithholdingForShareBasedCompensation_350" xlink:type="arc" order="2" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PaymentsRelatedToTaxWithholdingForShareBasedCompensation" xlink:label="loc_us-gaapPaymentsRelatedToTaxWithholdingForShareBasedCompensation_350" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapAccumulatedOtherComprehensiveIncomeLossLineItems" xlink:to="loc_us-gaapPaymentsRelatedToTaxWithholdingForShareBasedCompensation_350" xlink:type="arc" order="3" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockIssuedDuringPeriodValueEmployeeBenefitPlan" xlink:label="loc_us-gaapStockIssuedDuringPeriodValueEmployeeBenefitPlan_350" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapAccumulatedOtherComprehensiveIncomeLossLineItems" xlink:to="loc_us-gaapStockIssuedDuringPeriodValueEmployeeBenefitPlan_350" xlink:type="arc" order="4" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised" xlink:label="loc_us-gaapStockIssuedDuringPeriodSharesStockOptionsExercised_350" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapAccumulatedOtherComprehensiveIncomeLossLineItems" xlink:to="loc_us-gaapStockIssuedDuringPeriodSharesStockOptionsExercised_350" xlink:type="arc" order="5" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLowerRangeLimit" xlink:label="loc_us-gaapShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLowerRangeLimit_350" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapAccumulatedOtherComprehensiveIncomeLossLineItems" xlink:to="loc_us-gaapShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLowerRangeLimit_350" xlink:type="arc" order="6" />
      <link:loc xlink:type="locator" xlink:href="hrow-20250930.xsd#HROW_AddtionalSharesPaidForTaxWithholdingForShareBasedCompensation" xlink:label="loc_HROWAddtionalSharesPaidForTaxWithholdingForShareBasedCompensation_350" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapAccumulatedOtherComprehensiveIncomeLossLineItems" xlink:to="loc_HROWAddtionalSharesPaidForTaxWithholdingForShareBasedCompensation_350" xlink:type="arc" order="7" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ProceedsFromStockOptionsExercised" xlink:label="loc_us-gaapProceedsFromStockOptionsExercised_350" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapAccumulatedOtherComprehensiveIncomeLossLineItems" xlink:to="loc_us-gaapProceedsFromStockOptionsExercised_350" xlink:type="arc" order="8" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeUpperRangeLimit" xlink:label="loc_us-gaapShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeUpperRangeLimit_350" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapAccumulatedOtherComprehensiveIncomeLossLineItems" xlink:to="loc_us-gaapShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeUpperRangeLimit_350" xlink:type="arc" order="9" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockIssuedDuringPeriodValueRestrictedStockAwardGross" xlink:label="loc_us-gaapStockIssuedDuringPeriodValueRestrictedStockAwardGross_350" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapAccumulatedOtherComprehensiveIncomeLossLineItems" xlink:to="loc_us-gaapStockIssuedDuringPeriodValueRestrictedStockAwardGross_350" xlink:type="arc" order="10" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod" xlink:label="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_350" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapAccumulatedOtherComprehensiveIncomeLossLineItems" xlink:to="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_350" xlink:type="arc" order="11" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockIssuedDuringPeriodSharesIssuedForServices" xlink:label="loc_us-gaapStockIssuedDuringPeriodSharesIssuedForServices_350" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapAccumulatedOtherComprehensiveIncomeLossLineItems" xlink:to="loc_us-gaapStockIssuedDuringPeriodSharesIssuedForServices_350" xlink:type="arc" order="12" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SharePrice" xlink:label="loc_us-gaapSharePrice_350" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapAccumulatedOtherComprehensiveIncomeLossLineItems" xlink:to="loc_us-gaapSharePrice_350" xlink:type="arc" order="13" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingRights" xlink:label="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingRights_350" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapAccumulatedOtherComprehensiveIncomeLossLineItems" xlink:to="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingRights_350" xlink:type="arc" order="14" />
      <link:loc xlink:type="locator" xlink:href="hrow-20250930.xsd#HROW_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsForfeitureFactor" xlink:label="loc_HROWShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsForfeitureFactor_350" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapAccumulatedOtherComprehensiveIncomeLossLineItems" xlink:to="loc_HROWShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsForfeitureFactor_350" xlink:type="arc" order="15" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized" xlink:label="loc_us-gaapEmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized_350" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapAccumulatedOtherComprehensiveIncomeLossLineItems" xlink:to="loc_us-gaapEmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized_350" xlink:type="arc" order="16" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1" xlink:label="loc_us-gaapEmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_350" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapAccumulatedOtherComprehensiveIncomeLossLineItems" xlink:to="loc_us-gaapEmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_350" xlink:type="arc" order="17" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AllocatedShareBasedCompensationExpense" xlink:label="loc_us-gaapAllocatedShareBasedCompensationExpense_350" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapAccumulatedOtherComprehensiveIncomeLossLineItems" xlink:to="loc_us-gaapAllocatedShareBasedCompensationExpense_350" xlink:type="arc" order="18" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue" xlink:label="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue_350" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapAccumulatedOtherComprehensiveIncomeLossLineItems" xlink:to="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue_350" xlink:type="arc" order="19" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodTotalFairValue" xlink:label="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodTotalFairValue_350" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapAccumulatedOtherComprehensiveIncomeLossLineItems" xlink:to="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodTotalFairValue_350" xlink:type="arc" order="20" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1" xlink:label="loc_us-gaapSharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1_350" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapAccumulatedOtherComprehensiveIncomeLossLineItems" xlink:to="loc_us-gaapSharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1_350" xlink:type="arc" order="21" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate" xlink:label="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate_350" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapAccumulatedOtherComprehensiveIncomeLossLineItems" xlink:to="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate_350" xlink:type="arc" order="22" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate" xlink:label="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate_350" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapAccumulatedOtherComprehensiveIncomeLossLineItems" xlink:to="loc_us-gaapShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate_350" xlink:type="arc" order="23" />
      <link:loc xlink:type="locator" xlink:href="hrow-20250930.xsd#HROW_SharebasedCompensationArrangementBySharebasedPaymentAwardDerivedServicePeriod" xlink:label="loc_HROWSharebasedCompensationArrangementBySharebasedPaymentAwardDerivedServicePeriod_350" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapAccumulatedOtherComprehensiveIncomeLossLineItems" xlink:to="loc_HROWSharebasedCompensationArrangementBySharebasedPaymentAwardDerivedServicePeriod_350" xlink:type="arc" order="24" />
    </link:definitionLink>
    <link:definitionLink xlink:type="extended" xlink:role="http://harrow.com/role/CommitmentsAndContingenciesDetailsNarrative" xlink:title="999075 - Disclosure - COMMITMENTS AND CONTINGENCIES (Details Narrative)">
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LossContingenciesLineItems" xlink:label="loc_us-gaapLossContingenciesLineItems" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LossContingenciesTable" xlink:label="loc_us-gaapLossContingenciesTable" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xbrldt:contextElement="segment" xlink:from="loc_us-gaapLossContingenciesLineItems" xlink:to="loc_us-gaapLossContingenciesTable" xlink:type="arc" order="10" xbrldt:closed="true" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_LitigationCaseAxis" xlink:label="loc_srtLitigationCaseAxis" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaapLossContingenciesTable" xlink:to="loc_srtLitigationCaseAxis" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_LitigationCaseTypeDomain" xlink:label="loc_srtLitigationCaseTypeDomain" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srtLitigationCaseAxis" xlink:to="loc_srtLitigationCaseTypeDomain" xlink:type="arc" order="20" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_LitigationCaseTypeDomain" xlink:label="loc_srtLitigationCaseTypeDomain_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xbrldt:contextElement="segment" xlink:from="loc_srtLitigationCaseAxis" xlink:to="loc_srtLitigationCaseTypeDomain_10" xlink:type="arc" order="30" />
      <link:loc xlink:type="locator" xlink:href="hrow-20250930.xsd#HROW_OSRXLiabilityMember" xlink:label="loc_HROWOSRXLiabilityMember_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srtLitigationCaseTypeDomain" xlink:to="loc_HROWOSRXLiabilityMember_10" xlink:type="arc" order="11" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsequentEventTypeAxis" xlink:label="loc_us-gaapSubsequentEventTypeAxis" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaapLossContingenciesTable" xlink:to="loc_us-gaapSubsequentEventTypeAxis" xlink:type="arc" order="2" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsequentEventTypeDomain" xlink:label="loc_us-gaapSubsequentEventTypeDomain" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaapSubsequentEventTypeAxis" xlink:to="loc_us-gaapSubsequentEventTypeDomain" xlink:type="arc" order="20" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsequentEventTypeDomain" xlink:label="loc_us-gaapSubsequentEventTypeDomain_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xbrldt:contextElement="segment" xlink:from="loc_us-gaapSubsequentEventTypeAxis" xlink:to="loc_us-gaapSubsequentEventTypeDomain_10" xlink:type="arc" order="30" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsequentEventMember" xlink:label="loc_us-gaapSubsequentEventMember_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapSubsequentEventTypeDomain" xlink:to="loc_us-gaapSubsequentEventMember_10" xlink:type="arc" order="12" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TypeOfArrangementAxis" xlink:label="loc_us-gaapTypeOfArrangementAxis" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaapLossContingenciesTable" xlink:to="loc_us-gaapTypeOfArrangementAxis" xlink:type="arc" order="3" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember" xlink:label="loc_us-gaapArrangementsAndNonarrangementTransactionsMember" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaapTypeOfArrangementAxis" xlink:to="loc_us-gaapArrangementsAndNonarrangementTransactionsMember" xlink:type="arc" order="20" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember" xlink:label="loc_us-gaapArrangementsAndNonarrangementTransactionsMember_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xbrldt:contextElement="segment" xlink:from="loc_us-gaapTypeOfArrangementAxis" xlink:to="loc_us-gaapArrangementsAndNonarrangementTransactionsMember_10" xlink:type="arc" order="30" />
      <link:loc xlink:type="locator" xlink:href="hrow-20250930.xsd#HROW_FormosaAgreementMember" xlink:label="loc_HROWFormosaAgreementMember_20" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapArrangementsAndNonarrangementTransactionsMember" xlink:to="loc_HROWFormosaAgreementMember_20" xlink:type="arc" order="21" />
      <link:loc xlink:type="locator" xlink:href="hrow-20250930.xsd#HROW_AssetPurchaseLicenseandRelatedAgreementsMember" xlink:label="loc_HROWAssetPurchaseLicenseandRelatedAgreementsMember_30" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapArrangementsAndNonarrangementTransactionsMember" xlink:to="loc_HROWAssetPurchaseLicenseandRelatedAgreementsMember_30" xlink:type="arc" order="31" />
      <link:loc xlink:type="locator" xlink:href="hrow-20250930.xsd#HROW_MergerAgreementMember" xlink:label="loc_HROWMergerAgreementMember_70" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapArrangementsAndNonarrangementTransactionsMember" xlink:to="loc_HROWMergerAgreementMember_70" xlink:type="arc" order="72" />
      <link:loc xlink:type="locator" xlink:href="hrow-20250930.xsd#HROW_AssetPurchaseAndLicenseAgreementsMember" xlink:label="loc_HROWAssetPurchaseAndLicenseAgreementsMember_120" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapArrangementsAndNonarrangementTransactionsMember" xlink:to="loc_HROWAssetPurchaseAndLicenseAgreementsMember_120" xlink:type="arc" order="121" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis" xlink:label="loc_srtScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaapLossContingenciesTable" xlink:to="loc_srtScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis" xlink:type="arc" order="4" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_EquityMethodInvesteeNameDomain" xlink:label="loc_srtEquityMethodInvesteeNameDomain" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srtScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis" xlink:to="loc_srtEquityMethodInvesteeNameDomain" xlink:type="arc" order="20" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_EquityMethodInvesteeNameDomain" xlink:label="loc_srtEquityMethodInvesteeNameDomain_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xbrldt:contextElement="segment" xlink:from="loc_srtScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis" xlink:to="loc_srtEquityMethodInvesteeNameDomain_10" xlink:type="arc" order="30" />
      <link:loc xlink:type="locator" xlink:href="hrow-20250930.xsd#HROW_MeltsMember" xlink:label="loc_HROWMeltsMember_70" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srtEquityMethodInvesteeNameDomain" xlink:to="loc_HROWMeltsMember_70" xlink:type="arc" order="71" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeAxis" xlink:label="loc_srtRangeAxis" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaapLossContingenciesTable" xlink:to="loc_srtRangeAxis" xlink:type="arc" order="5" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember" xlink:label="loc_srtRangeMember" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srtRangeAxis" xlink:to="loc_srtRangeMember" xlink:type="arc" order="20" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember" xlink:label="loc_srtRangeMember_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xbrldt:contextElement="segment" xlink:from="loc_srtRangeAxis" xlink:to="loc_srtRangeMember_10" xlink:type="arc" order="30" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MinimumMember" xlink:label="loc_srtMinimumMember_100" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srtRangeMember" xlink:to="loc_srtMinimumMember_100" xlink:type="arc" order="101" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MaximumMember" xlink:label="loc_srtMaximumMember_110" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srtRangeMember" xlink:to="loc_srtMaximumMember_110" xlink:type="arc" order="111" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_StatementScenarioAxis" xlink:label="loc_srtStatementScenarioAxis" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaapLossContingenciesTable" xlink:to="loc_srtStatementScenarioAxis" xlink:type="arc" order="6" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ScenarioUnspecifiedDomain" xlink:label="loc_srtScenarioUnspecifiedDomain" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srtStatementScenarioAxis" xlink:to="loc_srtScenarioUnspecifiedDomain" xlink:type="arc" order="20" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ScenarioUnspecifiedDomain" xlink:label="loc_srtScenarioUnspecifiedDomain_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xbrldt:contextElement="segment" xlink:from="loc_srtStatementScenarioAxis" xlink:to="loc_srtScenarioUnspecifiedDomain_10" xlink:type="arc" order="30" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ScenarioForecastMember" xlink:label="loc_srtScenarioForecastMember_160" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srtScenarioUnspecifiedDomain" xlink:to="loc_srtScenarioForecastMember_160" xlink:type="arc" order="161" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ProceedsFromLegalSettlements" xlink:label="loc_us-gaapProceedsFromLegalSettlements_180" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapLossContingenciesLineItems" xlink:to="loc_us-gaapProceedsFromLegalSettlements_180" xlink:type="arc" order="0" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LossContingencyDamagesPaidValue" xlink:label="loc_us-gaapLossContingencyDamagesPaidValue_180" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapLossContingenciesLineItems" xlink:to="loc_us-gaapLossContingencyDamagesPaidValue_180" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LossContingencyDamagesSoughtValue" xlink:label="loc_us-gaapLossContingencyDamagesSoughtValue_180" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapLossContingenciesLineItems" xlink:to="loc_us-gaapLossContingencyDamagesSoughtValue_180" xlink:type="arc" order="2" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LitigationSettlementAmountAwardedToOtherParty" xlink:label="loc_us-gaapLitigationSettlementAmountAwardedToOtherParty_180" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapLossContingenciesLineItems" xlink:to="loc_us-gaapLitigationSettlementAmountAwardedToOtherParty_180" xlink:type="arc" order="3" />
      <link:loc xlink:type="locator" xlink:href="hrow-20250930.xsd#HROW_DescriptionOfLicensesAgreements" xlink:label="loc_HROWDescriptionOfLicensesAgreements_180" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapLossContingenciesLineItems" xlink:to="loc_HROWDescriptionOfLicensesAgreements_180" xlink:type="arc" order="4" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RoyaltyExpense" xlink:label="loc_us-gaapRoyaltyExpense_180" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapLossContingenciesLineItems" xlink:to="loc_us-gaapRoyaltyExpense_180" xlink:type="arc" order="5" />
      <link:loc xlink:type="locator" xlink:href="hrow-20250930.xsd#HROW_UpfrontAndMilestonePayments" xlink:label="loc_HROWUpfrontAndMilestonePayments_180" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapLossContingenciesLineItems" xlink:to="loc_HROWUpfrontAndMilestonePayments_180" xlink:type="arc" order="6" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityMethodInvestmentOwnershipPercentage" xlink:label="loc_us-gaapEquityMethodInvestmentOwnershipPercentage_180" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapLossContingenciesLineItems" xlink:to="loc_us-gaapEquityMethodInvestmentOwnershipPercentage_180" xlink:type="arc" order="7" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired" xlink:label="loc_us-gaapPaymentsToAcquireBusinessesNetOfCashAcquired_180" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapLossContingenciesLineItems" xlink:to="loc_us-gaapPaymentsToAcquireBusinessesNetOfCashAcquired_180" xlink:type="arc" order="8" />
      <link:loc xlink:type="locator" xlink:href="hrow-20250930.xsd#HROW_AaggregateAmountInCash" xlink:label="loc_HROWAaggregateAmountInCash_180" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapLossContingenciesLineItems" xlink:to="loc_HROWAaggregateAmountInCash_180" xlink:type="arc" order="9" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SharesIssued" xlink:label="loc_us-gaapSharesIssued_180" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapLossContingenciesLineItems" xlink:to="loc_us-gaapSharesIssued_180" xlink:type="arc" order="10" />
      <link:loc xlink:type="locator" xlink:href="hrow-20250930.xsd#HROW_AnnualNetSalesMilestones" xlink:label="loc_HROWAnnualNetSalesMilestones_180" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapLossContingenciesLineItems" xlink:to="loc_HROWAnnualNetSalesMilestones_180" xlink:type="arc" order="11" />
      <link:loc xlink:type="locator" xlink:href="hrow-20250930.xsd#HROW_TotalAnnualNetSalesMilestones" xlink:label="loc_HROWTotalAnnualNetSalesMilestones_180" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapLossContingenciesLineItems" xlink:to="loc_HROWTotalAnnualNetSalesMilestones_180" xlink:type="arc" order="12" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PurchaseCommitmentRemainingMinimumAmountCommitted" xlink:label="loc_us-gaapPurchaseCommitmentRemainingMinimumAmountCommitted_180" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapLossContingenciesLineItems" xlink:to="loc_us-gaapPurchaseCommitmentRemainingMinimumAmountCommitted_180" xlink:type="arc" order="13" />
    </link:definitionLink>
    <link:definitionLink xlink:type="extended" xlink:role="http://harrow.com/role/ScheduleOfSegmentNetRevenuesDetails" xlink:title="999076 - Disclosure - SCHEDULE OF SEGMENT NET REVENUES (Details)">
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentReportingInformationLineItems" xlink:label="loc_us-gaapSegmentReportingInformationLineItems" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable" xlink:label="loc_us-gaapScheduleOfSegmentReportingInformationBySegmentTable" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xbrldt:contextElement="segment" xlink:from="loc_us-gaapSegmentReportingInformationLineItems" xlink:to="loc_us-gaapScheduleOfSegmentReportingInformationBySegmentTable" xlink:type="arc" order="10" xbrldt:closed="true" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementBusinessSegmentsAxis" xlink:label="loc_us-gaapStatementBusinessSegmentsAxis" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaapScheduleOfSegmentReportingInformationBySegmentTable" xlink:to="loc_us-gaapStatementBusinessSegmentsAxis" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentDomain" xlink:label="loc_us-gaapSegmentDomain" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaapStatementBusinessSegmentsAxis" xlink:to="loc_us-gaapSegmentDomain" xlink:type="arc" order="20" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentDomain" xlink:label="loc_us-gaapSegmentDomain_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xbrldt:contextElement="segment" xlink:from="loc_us-gaapStatementBusinessSegmentsAxis" xlink:to="loc_us-gaapSegmentDomain_10" xlink:type="arc" order="30" />
      <link:loc xlink:type="locator" xlink:href="hrow-20250930.xsd#HROW_BrandedMember" xlink:label="loc_HROWBrandedMember_0" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapSegmentDomain" xlink:to="loc_HROWBrandedMember_0" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="hrow-20250930.xsd#HROW_CompoundingMember" xlink:label="loc_HROWCompoundingMember_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapSegmentDomain" xlink:to="loc_HROWCompoundingMember_10" xlink:type="arc" order="11" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CorporateMember" xlink:label="loc_us-gaapCorporateMember_240" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapSegmentDomain" xlink:to="loc_us-gaapCorporateMember_240" xlink:type="arc" order="241" />
      <link:loc xlink:type="locator" xlink:href="hrow-20250930.xsd#HROW_ReportableSegmentAggregationResearchAndDevelopmentMember" xlink:label="loc_HROWReportableSegmentAggregationResearchAndDevelopmentMember_260" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapSegmentDomain" xlink:to="loc_HROWReportableSegmentAggregationResearchAndDevelopmentMember_260" xlink:type="arc" order="261" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ProductOrServiceAxis" xlink:label="loc_srtProductOrServiceAxis" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaapScheduleOfSegmentReportingInformationBySegmentTable" xlink:to="loc_srtProductOrServiceAxis" xlink:type="arc" order="2" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ProductsAndServicesDomain" xlink:label="loc_srtProductsAndServicesDomain" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srtProductOrServiceAxis" xlink:to="loc_srtProductsAndServicesDomain" xlink:type="arc" order="20" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ProductsAndServicesDomain" xlink:label="loc_srtProductsAndServicesDomain_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xbrldt:contextElement="segment" xlink:from="loc_srtProductOrServiceAxis" xlink:to="loc_srtProductsAndServicesDomain_10" xlink:type="arc" order="30" />
      <link:loc xlink:type="locator" xlink:href="hrow-20250930.xsd#HROW_ProductSalesNetMember" xlink:label="loc_HROWProductSalesNetMember_0" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srtProductsAndServicesDomain" xlink:to="loc_HROWProductSalesNetMember_0" xlink:type="arc" order="2" />
      <link:loc xlink:type="locator" xlink:href="hrow-20250930.xsd#HROW_OtherRevenuesMember" xlink:label="loc_HROWOtherRevenuesMember_60" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srtProductsAndServicesDomain" xlink:to="loc_HROWOtherRevenuesMember_60" xlink:type="arc" order="62" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ConsolidationItemsAxis" xlink:label="loc_srtConsolidationItemsAxis" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaapScheduleOfSegmentReportingInformationBySegmentTable" xlink:to="loc_srtConsolidationItemsAxis" xlink:type="arc" order="3" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ConsolidationItemsDomain" xlink:label="loc_srtConsolidationItemsDomain" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srtConsolidationItemsAxis" xlink:to="loc_srtConsolidationItemsDomain" xlink:type="arc" order="20" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ConsolidationItemsDomain" xlink:label="loc_srtConsolidationItemsDomain_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xbrldt:contextElement="segment" xlink:from="loc_srtConsolidationItemsAxis" xlink:to="loc_srtConsolidationItemsDomain_10" xlink:type="arc" order="30" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OperatingSegmentsMember" xlink:label="loc_us-gaapOperatingSegmentsMember_180" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srtConsolidationItemsDomain" xlink:to="loc_us-gaapOperatingSegmentsMember_180" xlink:type="arc" order="182" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax" xlink:label="loc_us-gaapRevenueFromContractWithCustomerExcludingAssessedTax_570" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapSegmentReportingInformationLineItems" xlink:to="loc_us-gaapRevenueFromContractWithCustomerExcludingAssessedTax_570" xlink:type="arc" order="0" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CostOfGoodsAndServicesSold" xlink:label="loc_us-gaapCostOfGoodsAndServicesSold_570" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapSegmentReportingInformationLineItems" xlink:to="loc_us-gaapCostOfGoodsAndServicesSold_570" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_GrossProfit" xlink:label="loc_us-gaapGrossProfit_570" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapSegmentReportingInformationLineItems" xlink:to="loc_us-gaapGrossProfit_570" xlink:type="arc" order="2" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OperatingExpensesAbstract" xlink:label="loc_us-gaapOperatingExpensesAbstract_570" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapSegmentReportingInformationLineItems" xlink:to="loc_us-gaapOperatingExpensesAbstract_570" xlink:type="arc" order="3" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SellingGeneralAndAdministrativeExpense" xlink:label="loc_us-gaapSellingGeneralAndAdministrativeExpense_570" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapOperatingExpensesAbstract_570" xlink:to="loc_us-gaapSellingGeneralAndAdministrativeExpense_570" xlink:type="arc" order="4" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ResearchAndDevelopmentExpense" xlink:label="loc_us-gaapResearchAndDevelopmentExpense_570" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapOperatingExpensesAbstract_570" xlink:to="loc_us-gaapResearchAndDevelopmentExpense_570" xlink:type="arc" order="5" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OperatingExpenses" xlink:label="loc_us-gaapOperatingExpenses_570" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapSegmentReportingInformationLineItems" xlink:to="loc_us-gaapOperatingExpenses_570" xlink:type="arc" order="6" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OperatingIncomeLoss" xlink:label="loc_us-gaapOperatingIncomeLoss_570" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapSegmentReportingInformationLineItems" xlink:to="loc_us-gaapOperatingIncomeLoss_570" xlink:type="arc" order="7" />
    </link:definitionLink>
    <link:definitionLink xlink:type="extended" xlink:role="http://harrow.com/role/ScheduleOfRevenuesBySegmentDetails" xlink:title="999077 - Disclosure - SCHEDULE OF REVENUES BY SEGMENT (Details)">
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EntityWideInformationRevenueFromExternalCustomerLineItems" xlink:label="loc_us-gaapEntityWideInformationRevenueFromExternalCustomerLineItems" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfEntityWideInformationRevenueFromExternalCustomersByProductsAndServicesTable" xlink:label="loc_us-gaapScheduleOfEntityWideInformationRevenueFromExternalCustomersByProductsAndServicesTable" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xbrldt:contextElement="segment" xlink:from="loc_us-gaapEntityWideInformationRevenueFromExternalCustomerLineItems" xlink:to="loc_us-gaapScheduleOfEntityWideInformationRevenueFromExternalCustomersByProductsAndServicesTable" xlink:type="arc" order="10" xbrldt:closed="true" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ProductOrServiceAxis" xlink:label="loc_srtProductOrServiceAxis" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaapScheduleOfEntityWideInformationRevenueFromExternalCustomersByProductsAndServicesTable" xlink:to="loc_srtProductOrServiceAxis" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ProductsAndServicesDomain" xlink:label="loc_srtProductsAndServicesDomain" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srtProductOrServiceAxis" xlink:to="loc_srtProductsAndServicesDomain" xlink:type="arc" order="20" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ProductsAndServicesDomain" xlink:label="loc_srtProductsAndServicesDomain_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xbrldt:contextElement="segment" xlink:from="loc_srtProductOrServiceAxis" xlink:to="loc_srtProductsAndServicesDomain_10" xlink:type="arc" order="30" />
      <link:loc xlink:type="locator" xlink:href="hrow-20250930.xsd#HROW_IHEEZOMember" xlink:label="loc_HROWIHEEZOMember_0" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srtProductsAndServicesDomain" xlink:to="loc_HROWIHEEZOMember_0" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="hrow-20250930.xsd#HROW_VEVYEMember" xlink:label="loc_HROWVEVYEMember_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srtProductsAndServicesDomain" xlink:to="loc_HROWVEVYEMember_40" xlink:type="arc" order="41" />
      <link:loc xlink:type="locator" xlink:href="hrow-20250930.xsd#HROW_OtherProductsMember" xlink:label="loc_HROWOtherProductsMember_80" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srtProductsAndServicesDomain" xlink:to="loc_HROWOtherProductsMember_80" xlink:type="arc" order="81" />
      <link:loc xlink:type="locator" xlink:href="hrow-20250930.xsd#HROW_OtherRevenueMember" xlink:label="loc_HROWOtherRevenueMember_120" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srtProductsAndServicesDomain" xlink:to="loc_HROWOtherRevenueMember_120" xlink:type="arc" order="121" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementBusinessSegmentsAxis" xlink:label="loc_us-gaapStatementBusinessSegmentsAxis" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaapScheduleOfEntityWideInformationRevenueFromExternalCustomersByProductsAndServicesTable" xlink:to="loc_us-gaapStatementBusinessSegmentsAxis" xlink:type="arc" order="2" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentDomain" xlink:label="loc_us-gaapSegmentDomain" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaapStatementBusinessSegmentsAxis" xlink:to="loc_us-gaapSegmentDomain" xlink:type="arc" order="20" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentDomain" xlink:label="loc_us-gaapSegmentDomain_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xbrldt:contextElement="segment" xlink:from="loc_us-gaapStatementBusinessSegmentsAxis" xlink:to="loc_us-gaapSegmentDomain_10" xlink:type="arc" order="30" />
      <link:loc xlink:type="locator" xlink:href="hrow-20250930.xsd#HROW_BrandedMember" xlink:label="loc_HROWBrandedMember_160" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapSegmentDomain" xlink:to="loc_HROWBrandedMember_160" xlink:type="arc" order="161" />
      <link:loc xlink:type="locator" xlink:href="hrow-20250930.xsd#HROW_ImprimisRxMember" xlink:label="loc_HROWImprimisRxMember_200" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapSegmentDomain" xlink:to="loc_HROWImprimisRxMember_200" xlink:type="arc" order="201" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_Revenues" xlink:label="loc_us-gaapRevenues_290" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapEntityWideInformationRevenueFromExternalCustomerLineItems" xlink:to="loc_us-gaapRevenues_290" xlink:type="arc" order="0" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax" xlink:label="loc_us-gaapRevenueFromContractWithCustomerExcludingAssessedTax_290" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapEntityWideInformationRevenueFromExternalCustomerLineItems" xlink:to="loc_us-gaapRevenueFromContractWithCustomerExcludingAssessedTax_290" xlink:type="arc" order="1" />
    </link:definitionLink>
    <link:definitionLink xlink:type="extended" xlink:role="http://harrow.com/role/SegmentsAndConcentrationsDetailsNarrative" xlink:title="999078 - Disclosure - SEGMENTS AND CONCENTRATIONS (Details Narrative)">
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EntityWideRevenueMajorCustomerLineItems" xlink:label="loc_us-gaapEntityWideRevenueMajorCustomerLineItems" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfEntityWideRevenueByMajorCustomersByReportingSegmentsTable" xlink:label="loc_us-gaapScheduleOfEntityWideRevenueByMajorCustomersByReportingSegmentsTable" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xbrldt:contextElement="segment" xlink:from="loc_us-gaapEntityWideRevenueMajorCustomerLineItems" xlink:to="loc_us-gaapScheduleOfEntityWideRevenueByMajorCustomersByReportingSegmentsTable" xlink:type="arc" order="10" xbrldt:closed="true" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MajorCustomersAxis" xlink:label="loc_srtMajorCustomersAxis" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaapScheduleOfEntityWideRevenueByMajorCustomersByReportingSegmentsTable" xlink:to="loc_srtMajorCustomersAxis" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_NameOfMajorCustomerDomain" xlink:label="loc_srtNameOfMajorCustomerDomain" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srtMajorCustomersAxis" xlink:to="loc_srtNameOfMajorCustomerDomain" xlink:type="arc" order="20" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_NameOfMajorCustomerDomain" xlink:label="loc_srtNameOfMajorCustomerDomain_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xbrldt:contextElement="segment" xlink:from="loc_srtMajorCustomersAxis" xlink:to="loc_srtNameOfMajorCustomerDomain_10" xlink:type="arc" order="30" />
      <link:loc xlink:type="locator" xlink:href="hrow-20250930.xsd#HROW_TwoCustomerMember" xlink:label="loc_HROWTwoCustomerMember_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srtNameOfMajorCustomerDomain" xlink:to="loc_HROWTwoCustomerMember_10" xlink:type="arc" order="11" />
      <link:loc xlink:type="locator" xlink:href="hrow-20250930.xsd#HROW_OneCustomerMember" xlink:label="loc_HROWOneCustomerMember_30" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srtNameOfMajorCustomerDomain" xlink:to="loc_HROWOneCustomerMember_30" xlink:type="arc" order="31" />
      <link:loc xlink:type="locator" xlink:href="hrow-20250930.xsd#HROW_CustomerMember" xlink:label="loc_HROWCustomerMember_50" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srtNameOfMajorCustomerDomain" xlink:to="loc_HROWCustomerMember_50" xlink:type="arc" order="51" />
      <link:loc xlink:type="locator" xlink:href="hrow-20250930.xsd#HROW_TwoSuppliersMember" xlink:label="loc_HROWTwoSuppliersMember_90" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srtNameOfMajorCustomerDomain" xlink:to="loc_HROWTwoSuppliersMember_90" xlink:type="arc" order="91" />
      <link:loc xlink:type="locator" xlink:href="hrow-20250930.xsd#HROW_ThreeSuppliersMember" xlink:label="loc_HROWThreeSuppliersMember_110" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srtNameOfMajorCustomerDomain" xlink:to="loc_HROWThreeSuppliersMember_110" xlink:type="arc" order="111" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskByBenchmarkAxis" xlink:label="loc_us-gaapConcentrationRiskByBenchmarkAxis" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaapScheduleOfEntityWideRevenueByMajorCustomersByReportingSegmentsTable" xlink:to="loc_us-gaapConcentrationRiskByBenchmarkAxis" xlink:type="arc" order="2" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskBenchmarkDomain" xlink:label="loc_us-gaapConcentrationRiskBenchmarkDomain" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaapConcentrationRiskByBenchmarkAxis" xlink:to="loc_us-gaapConcentrationRiskBenchmarkDomain" xlink:type="arc" order="20" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskBenchmarkDomain" xlink:label="loc_us-gaapConcentrationRiskBenchmarkDomain_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xbrldt:contextElement="segment" xlink:from="loc_us-gaapConcentrationRiskByBenchmarkAxis" xlink:to="loc_us-gaapConcentrationRiskBenchmarkDomain_10" xlink:type="arc" order="30" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SalesRevenueNetMember" xlink:label="loc_us-gaapSalesRevenueNetMember_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapConcentrationRiskBenchmarkDomain" xlink:to="loc_us-gaapSalesRevenueNetMember_10" xlink:type="arc" order="12" />
      <link:loc xlink:type="locator" xlink:href="hrow-20250930.xsd#HROW_PurchasesMember" xlink:label="loc_HROWPurchasesMember_90" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapConcentrationRiskBenchmarkDomain" xlink:to="loc_HROWPurchasesMember_90" xlink:type="arc" order="92" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskByTypeAxis" xlink:label="loc_us-gaapConcentrationRiskByTypeAxis" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaapScheduleOfEntityWideRevenueByMajorCustomersByReportingSegmentsTable" xlink:to="loc_us-gaapConcentrationRiskByTypeAxis" xlink:type="arc" order="3" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskTypeDomain" xlink:label="loc_us-gaapConcentrationRiskTypeDomain" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaapConcentrationRiskByTypeAxis" xlink:to="loc_us-gaapConcentrationRiskTypeDomain" xlink:type="arc" order="20" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskTypeDomain" xlink:label="loc_us-gaapConcentrationRiskTypeDomain_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xbrldt:contextElement="segment" xlink:from="loc_us-gaapConcentrationRiskByTypeAxis" xlink:to="loc_us-gaapConcentrationRiskTypeDomain_10" xlink:type="arc" order="30" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CustomerConcentrationRiskMember" xlink:label="loc_us-gaapCustomerConcentrationRiskMember_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapConcentrationRiskTypeDomain" xlink:to="loc_us-gaapCustomerConcentrationRiskMember_10" xlink:type="arc" order="13" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SupplierConcentrationRiskMember" xlink:label="loc_us-gaapSupplierConcentrationRiskMember_90" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapConcentrationRiskTypeDomain" xlink:to="loc_us-gaapSupplierConcentrationRiskMember_90" xlink:type="arc" order="93" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NumberOfReportableSegments" xlink:label="loc_us-gaapNumberOfReportableSegments_160" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapEntityWideRevenueMajorCustomerLineItems" xlink:to="loc_us-gaapNumberOfReportableSegments_160" xlink:type="arc" order="0" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskPercentage1" xlink:label="loc_us-gaapConcentrationRiskPercentage1_160" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapEntityWideRevenueMajorCustomerLineItems" xlink:to="loc_us-gaapConcentrationRiskPercentage1_160" xlink:type="arc" order="1" />
    </link:definitionLink>
    <link:definitionLink xlink:type="extended" xlink:role="http://harrow.com/role/SubsequentEventsDetailsNarrative" xlink:title="999079 - Disclosure - SUBSEQUENT EVENTS (Details Narrative)">
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaapStatementLineItems" />
      <link:loc xlink:type="locator" xlink:href="hrow-20250930.xsd#HROW_SubsequentEventsTable" xlink:label="loc_HROWSubsequentEventsTable" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xbrldt:contextElement="segment" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_HROWSubsequentEventsTable" xlink:type="arc" order="10" xbrldt:closed="true" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementEquityComponentsAxis" xlink:label="loc_us-gaapStatementEquityComponentsAxis" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_HROWSubsequentEventsTable" xlink:to="loc_us-gaapStatementEquityComponentsAxis" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityComponentDomain" xlink:label="loc_us-gaapEquityComponentDomain" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaapStatementEquityComponentsAxis" xlink:to="loc_us-gaapEquityComponentDomain" xlink:type="arc" order="20" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityComponentDomain" xlink:label="loc_us-gaapEquityComponentDomain_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xbrldt:contextElement="segment" xlink:from="loc_us-gaapStatementEquityComponentsAxis" xlink:to="loc_us-gaapEquityComponentDomain_10" xlink:type="arc" order="30" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockMember" xlink:label="loc_us-gaapCommonStockMember_0" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapEquityComponentDomain" xlink:to="loc_us-gaapCommonStockMember_0" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AwardTypeAxis" xlink:label="loc_us-gaapAwardTypeAxis" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_HROWSubsequentEventsTable" xlink:to="loc_us-gaapAwardTypeAxis" xlink:type="arc" order="2" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="loc_us-gaapShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaapAwardTypeAxis" xlink:to="loc_us-gaapShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:type="arc" order="20" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="loc_us-gaapShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xbrldt:contextElement="segment" xlink:from="loc_us-gaapAwardTypeAxis" xlink:to="loc_us-gaapShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_10" xlink:type="arc" order="30" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EmployeeStockOptionMember" xlink:label="loc_us-gaapEmployeeStockOptionMember_0" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:to="loc_us-gaapEmployeeStockOptionMember_0" xlink:type="arc" order="2" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestrictedStockUnitsRSUMember" xlink:label="loc_us-gaapRestrictedStockUnitsRSUMember_40" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:to="loc_us-gaapRestrictedStockUnitsRSUMember_40" xlink:type="arc" order="41" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeAxis" xlink:label="loc_srtRangeAxis" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_HROWSubsequentEventsTable" xlink:to="loc_srtRangeAxis" xlink:type="arc" order="3" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember" xlink:label="loc_srtRangeMember" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srtRangeAxis" xlink:to="loc_srtRangeMember" xlink:type="arc" order="20" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember" xlink:label="loc_srtRangeMember_10" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xbrldt:contextElement="segment" xlink:from="loc_srtRangeAxis" xlink:to="loc_srtRangeMember_10" xlink:type="arc" order="30" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MinimumMember" xlink:label="loc_srtMinimumMember_20" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srtRangeMember" xlink:to="loc_srtMinimumMember_20" xlink:type="arc" order="22" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MaximumMember" xlink:label="loc_srtMaximumMember_30" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srtRangeMember" xlink:to="loc_srtMaximumMember_30" xlink:type="arc" order="32" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockIssuedDuringPeriodSharesNewIssues" xlink:label="loc_us-gaapStockIssuedDuringPeriodSharesNewIssues_70" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapStockIssuedDuringPeriodSharesNewIssues_70" xlink:type="arc" order="0" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ProceedsFromStockOptionsExercised" xlink:label="loc_us-gaapProceedsFromStockOptionsExercised_70" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapProceedsFromStockOptionsExercised_70" xlink:type="arc" order="1" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised" xlink:label="loc_us-gaapStockIssuedDuringPeriodSharesStockOptionsExercised_70" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapStockIssuedDuringPeriodSharesStockOptionsExercised_70" xlink:type="arc" order="2" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLowerRangeLimit" xlink:label="loc_us-gaapShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLowerRangeLimit_70" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLowerRangeLimit_70" xlink:type="arc" order="3" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockIssuedDuringPeriodValueRestrictedStockAwardGross" xlink:label="loc_us-gaapStockIssuedDuringPeriodValueRestrictedStockAwardGross_70" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapStockIssuedDuringPeriodValueRestrictedStockAwardGross_70" xlink:type="arc" order="4" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PaymentsRelatedToTaxWithholdingForShareBasedCompensation" xlink:label="loc_us-gaapPaymentsRelatedToTaxWithholdingForShareBasedCompensation_70" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapStatementLineItems" xlink:to="loc_us-gaapPaymentsRelatedToTaxWithholdingForShareBasedCompensation_70" xlink:type="arc" order="5" />
    </link:definitionLink>
    <link:definitionLink xlink:type="extended" xlink:role="http://xbrl.sec.gov/ecd/role/PvpExecutiveCategoriesOnly" />
    <link:definitionLink xlink:type="extended" xlink:role="http://xbrl.sec.gov/ecd/role/PvpAdjustmentsOnly" />
    <link:definitionLink xlink:type="extended" xlink:role="http://xbrl.sec.gov/ecd/role/IndividualsOnly" />
    <link:definitionLink xlink:type="extended" xlink:role="http://xbrl.sec.gov/ecd/AwardTypeOnly">
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="loc_us-gaapShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" />
      <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SecuredOvernightFinancingRateSofrMember" xlink:label="loc_us-gaapSecuredOvernightFinancingRateSofrMember" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:to="loc_us-gaapSecuredOvernightFinancingRateSofrMember" xlink:type="arc" order="0" />
      <link:loc xlink:type="locator" xlink:href="hrow-20250930.xsd#HROW_RSUAndPSUMember" xlink:label="loc_HROWRSUAndPSUMember" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:to="loc_HROWRSUAndPSUMember" xlink:type="arc" order="10" />
      <link:loc xlink:type="locator" xlink:href="hrow-20250930.xsd#HROW_PerformanceStockUnitsPSUMember" xlink:label="loc_HROWPerformanceStockUnitsPSUMember" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:to="loc_HROWPerformanceStockUnitsPSUMember" xlink:type="arc" order="20" />
      <link:loc xlink:type="locator" xlink:href="hrow-20250930.xsd#HROW_StockOptionPlanOneMember" xlink:label="loc_HROWStockOptionPlanOneMember" />
      <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaapShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:to="loc_HROWStockOptionPlanOneMember" xlink:type="arc" order="30" />
    </link:definitionLink>
    <link:definitionLink xlink:type="extended" xlink:role="http://xbrl.sec.gov/ecd/role/TradingArrangementsOnly" />
</link:linkbase>
