<?xml version="1.0" encoding="us-ascii"?>
<!-- DFIN ActiveDisclosure(SM) XBRL Schema Document - http://www.dfinsolutions.com/ -->
<!-- Creation Date      : 2020-03-13T17:34:09.1120506+00:00 -->
<!-- Version            : 5.0.1.369 -->
<!-- Package ID         : 950ccd1d4035488fbdbb46b3f5be7559 -->
<!-- Copyright (c) 2020 Donnelley Financial Solutions, Inc. All Rights Reserved. -->
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  <xsd:element id="clsd_EmployeeStockPurchasePlanPayrollDeductionAsPercentageOfRegularEmployeeEarningsMaximum" name="EmployeeStockPurchasePlanPayrollDeductionAsPercentageOfRegularEmployeeEarningsMaximum" type="num:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="clsd_CommonStockAvailableForIssuanceIncreaseInPeriod" name="CommonStockAvailableForIssuanceIncreaseInPeriod" type="xbrli:durationItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="clsd_AdditionOfCommonStockSharesReservedForFutureIssuance" name="AdditionOfCommonStockSharesReservedForFutureIssuance" type="xbrli:sharesItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" />
  <xsd:element id="clsd_IncomeTaxDisclosureLineItems" name="IncomeTaxDisclosureLineItems" type="xbrli:stringItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="clsd_IncomeTaxDisclosureTable" name="IncomeTaxDisclosureTable" type="xbrli:stringItemType" substitutionGroup="xbrldt:hypercubeItem" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="clsd_USFederalStateIncomeTaxMember" name="USFederalStateIncomeTaxMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="clsd_DeferredTaxAssetsTaxNonDeductibleAccrualsAccruedExpenses" name="DeferredTaxAssetsTaxNonDeductibleAccrualsAccruedExpenses" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="clsd_DeferredTaxLiabilitiesRightOfUseAssets" name="DeferredTaxLiabilitiesRightOfUseAssets" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="credit" />
  <xsd:element id="clsd_DeferredTaxAssetsLeaseLiability" name="DeferredTaxAssetsLeaseLiability" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="clsd_DeferredTaxLiabilitiesDepreciationDifferences" name="DeferredTaxLiabilitiesDepreciationDifferences" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="credit" />
  <xsd:element id="clsd_DeferredTaxAssetsDisallowedInterestExpense" name="DeferredTaxAssetsDisallowedInterestExpense" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="clsd_OperatingLossCarryforwardsExpirationPeriod" name="OperatingLossCarryforwardsExpirationPeriod" type="xbrli:gYearItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="clsd_BaseAnnualRentalIncomeFixedPercentageIncrease" name="BaseAnnualRentalIncomeFixedPercentageIncrease" type="num:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="clsd_OperatingLeasesRentExpenseMinimumRentalsPerMonth" name="OperatingLeasesRentExpenseMinimumRentalsPerMonth" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="clsd_AreaOfLeasedOfficeSpace" name="AreaOfLeasedOfficeSpace" type="num:areaItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" />
  <xsd:element id="clsd_CommitmentAndContingenciesLineItems" name="CommitmentAndContingenciesLineItems" type="xbrli:stringItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="clsd_CommitmentAndContingenciesTable" name="CommitmentAndContingenciesTable" type="xbrli:stringItemType" substitutionGroup="xbrldt:hypercubeItem" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="clsd_ManufacturingSupplyAgreementMember" name="ManufacturingSupplyAgreementMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="clsd_GerresheimerRegensburgGmbHMember" name="GerresheimerRegensburgGmbHMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="clsd_IncrementalBorrowingRate" name="IncrementalBorrowingRate" type="num:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" />
  <xsd:element id="clsd_InitialTermOfAgreement" name="InitialTermOfAgreement" type="xbrli:durationItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="clsd_RenewalTermOfAgreement" name="RenewalTermOfAgreement" type="xbrli:durationItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="clsd_AdditionalMilestonePayment" name="AdditionalMilestonePayment" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="clsd_PreLaunchMilestonePayments" name="PreLaunchMilestonePayments" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="clsd_FirstCumulativeNetSalesOfProducts" name="FirstCumulativeNetSalesOfProducts" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit" />
  <xsd:element id="clsd_UpfrontPayments" name="UpfrontPayments" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="clsd_BauschHealthIrelandLimitedMember" name="BauschHealthIrelandLimitedMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="clsd_CommercialArrangementMember" name="CommercialArrangementMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="clsd_LicenseArrangementMember" name="LicenseArrangementMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="clsd_REGENXBIOIncMember" name="REGENXBIOIncMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="clsd_OptionFeePaid" name="OptionFeePaid" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="clsd_MilestonePayments" name="MilestonePayments" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="clsd_ProceedsFromOptionFeePreviouslyReceived" name="ProceedsFromOptionFeePreviouslyReceived" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit" />
  <xsd:element id="clsd_SalesBasedMilestonePayments" name="SalesBasedMilestonePayments" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="clsd_FairValueAssetsBetweenLevel1Level2AndLevel3TransfersAmount" name="FairValueAssetsBetweenLevel1Level2AndLevel3TransfersAmount" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="clsd_CashAndMoneyMarketsMember" name="CashAndMoneyMarketsMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="clsd_RestrictedCashMoneyMarketMember" name="RestrictedCashMoneyMarketMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="clsd_NonVestedRestrictedStockUnitsMember" name="NonVestedRestrictedStockUnitsMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="clsd_HatterasVenturePartnersIVSBICLPMember" name="HatterasVenturePartnersIVSBICLPMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="clsd_HatterasVenturePartnersIVLPMember" name="HatterasVenturePartnersIVLPMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="clsd_ClinicalTrialsMember" name="ClinicalTrialsMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="clsd_SAPHHIREMember" name="SAPHHIREMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="clsd_TOPAZMember" name="TOPAZMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="clsd_AmountOfUpfrontPaymentAndDevelopmentMilestonesPaymentToBeReceivedUnderLicenseAgreement" name="AmountOfUpfrontPaymentAndDevelopmentMilestonesPaymentToBeReceivedUnderLicenseAgreement" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="clsd_DevelopmentMilestonePayments" name="DevelopmentMilestonePayments" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="clsd_ThresholdPercentageOfSalesForTieredRoyalties" name="ThresholdPercentageOfSalesForTieredRoyalties" type="num:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="clsd_ArcticVisionLimitedMember" name="ArcticVisionLimitedMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
</xsd:schema>
