Surgical Technique for DMEK - Mosby · Keratoplasty. Section 6. Endothelial Keratoplasty. Chapter . 131. Surgical Technique for DMEK. Kevin J. Shah, Michael D. Straiko, Mark A. Greiner.

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Part ix Keratoplasty

Section 6 Endothelial Keratoplasty

Chapter 131

Surgical Technique for DMEKKevin J. Shah, Michael D. Straiko, Mark A. Greiner

sequentialapproachtothistechniqueandhighlightsseveralvital intraoperative techniques that can make DMEK areproducible,predictable,andsuccessfulprocedure.

Injectors

OneofthekeystepsinDMEKsurgeryisthesafeandcon-trolleddeliveryofthefragileDMEKscrollintotheanteriorchamber. The ideal DMEK injector should have multiplefeaturesincluding:

• Aclosedsystemthatpreventsbackflowfromtheanteriorchamberandiscapableofmaintaininganteriorchambervolume

• Amaterialthatissafefortheendothelium• Noneedforviscoelastic• Easyloadingwithminimalhandlingofthegraft• Anadequatecalibertoavoidcompressionofthegraft• Ataperedtiptosealthesurgicalincisionwell.

Currently there are no FDA-approved DMEK injectors.American surgeons have found many creative off-labelmethodsaroundthisobstacle.Manysurgeonsusemodifiedintraocularlensinjectioncartridgesforthispurpose.1–4TheStaarmicroinjector(StaarSurgicalCompany,Monrovia,CA)was one of the most common inserters initially used forDMEKintheUS(Fig.131.1B).TheStaarinjectorisanopensystemwithafoamplungerandrequiresaviscoelasticagenttohelpdeliverthetissue.Thistechniqueriskstheintroduc-tionofviscoelasticintotheanteriorchamberduringtissueinjection, which can impede graft attachment.5 AnotherpopularIOLcartridgebasedsystemistheViscojectIOLinjec-tor(Bausch&Lomb,AlisoViejo,CA)(Fig.131.1A).ThePricegroupreportedimprovedrebubblerateswhentransitioningfrom the Staar injector with the use of viscoelastic to theViscoject,whichdoesnotrequireviscoelasticandisasmallclosed-systeminserter.6

Asimilarclosed-systeminjectorcanbecreatedwiththeAMOEmeraldOneSeriesIOLcartridge(AbbotLaboratoriesInc.,AbbotPark,IL),withafewkeydifferencescomparedtootherIOLcartridgeinjectors(Fig.131.1D).Assembledwitha standard Luer-Lok syringe filled with BSS and 14-Frenchgauge nasogastric tubing, the Emerald One Series IOL car-tridge is large enough that it can be used to aspirate thegraftintotheinjectorandsmallenoughtobeusedthrougha2.75mmclearcornealincision.Similartootherinjectors

Key Concepts

• Aclosed-systeminjectorisidealforcontrolleddeliveryofaDMEKgraft.

• Creatingarecipientstromalbedofslightlygreaterdiameterthanthedonorgraftimprovesgraftattachment.

• Creatingaperipheraliridotomyisvitalinpreventingpupillaryblock.

• Obtainingcorrectgraftorientationiscriticalforasuccessfuloutcome.

• TheprimarytechniquesusedtounfoldandcenteraDMEKgraftincludefluidorairinjection,cornealtapping,and/oranteriorchamberdepthmodulation.

• Theuseofsulfurhexafluoride20%hasdecreasedgraftdetachmentrates.

Introduction

Descemetmembraneendothelialkeratoplasty(DMEK)istheonly surgical procedure that provides a true anatomicexchangeofdiseasedendotheliumandDescemetmembranewithhealthydonor tissue.Thereare several advantagesofDMEKcomparedtoDescemetstrippingendothelialkeroto-plasty (DSEK), includingfastervisual recovery, lowerrejec-tion rate, and higher quality of vision. However, graftpreparation,iatrogenicgraftfailure,andpreviouslyreportedhighratesofgraftdetachmentareobstaclesthathavepre-ventedmanycorneal surgeons fromadopting this surgery.WitheyebanksnowpreparingDMEKtissue,morecornealsurgeons are beginning to adopt DMEK as the risk of pre-operativetissuelosshasbeeneliminated.

Similar to DSEK, all corneal surgeons will experience alearning curve with DMEK and should select their firstpatients keeping this in mind. This chapter discusses theauthors’ experiences performing DMEK and provides aliterature-basedreviewofsurgicaltechniquesthathavebeenimplementedwithDMEK.While the techniquesnecessarytoperformDMEKaredifferent thanDSEK, successful out-comes can be achieved routinely. This chapter outlines a

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CHAPTER 131

surgicalTechniqueforDMEK

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Chapter Outline

IntroductionInjectorsrecipientpreparationWoundCreationGraftOrientationUnscrollingandCenteringGraftTamponadeWithAirorsulfurHexafluoride20%

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Section 6 EndothelialKeratoplasty

allowsslow,controlleddeliveryoftissuewithoptimalante-rior chamber maintenance. An additional feature of theDMEK Jones tube is a central dilation, which results indecreasedfluidvelocityinthecentralportionoftheinjectorrelative to the tip. This differential in velocity helps topreventexcessivegraftaspirationandmaximizecontrolofgraftdelivery.

With all closed-system DMEK injectors, care must betakentoavoidover-pressurizationoftheanteriorchamber.InjectionofexcessBSScreatesanunfavorablepressuregradi-entthatcanresult inejectionor incarcerationofthegraftwhentheinjectortipiswithdrawn.Toavoidthissituation,theauthorsrecommendreleasingfluidfromaparacentesispriortowithdrawingtheinjector,oratanytimethesurgeonfeels the eye is becoming over-pressurized. Additionally,shallowing the anterior chamber after graft insertion andpriortoinjectorremovalcanmaintaingraftorientationandsimultaneouslybegintheunfoldingprocess.Anothertech-nique for reducing graft ejection is by pressing a secondinstrument(e.g.30-Gcannula)atopthemainincisionwhilewithdrawingtheinjector,essentiallycreatinga“trapdoor”at the wound. It is also helpful in many situations toposition thegraftnear theopeningof the injector so thatit is introduced into the eye with minimal influx of BSS(Video131.1).

madeofclearortranslucentmaterials,graftorientationcanoftenbemaintainedduring injection.Theauthors suggestusing a 1mL or 3mL Luer-Lok syringe with this injectorto further enhance controlled delivery into the anteriorchamber.Anoptional3-waystopcockcanalsobeaddedtothe injector for safety to removeairbubbles and refill thesyringewithoutdisturbingtheloadedgraft(Fig.131.1D).

Glass injectors have been promoted in the Europeanliterature.7–9SeveralEuropeantechniquesutilizeglassinjec-tors such as the curved glass pipette made by the DutchOphthalmicResearchCenter(DMEKsurgicaldisposableset;DORC, Zuidland, The Netherlands) or the Geuder glassinjector (Geuder AG, Heidelberg, Germany). Glass poten-tiallyoffersasmoothersurfacethanplasticandmaycauseless endothelial cell damage. Surgeons have also adoptedoff-labeluseofaglassJonestube(DMEKJonestube#80000-DMEK,GuntherWeissScientific,Portland,OR).JonestubesareFDAapprovedforlacrimalsurgery.Similartothemodi-fiedAMOinjector,theJonestubecanbeusedtoaspiratethegraft into the inserter, reducing forceps contact with thegraftandtheriskofendothelialcelltrauma.Coupledwith14-French gauge nasogastric tubing, the Jones tube isattached to a3mLor5mL syringe full ofBSS, creating aclosedsystemwithafluidreservoirfortissueinjectionandchamber maintenance (Fig. 131.1C). The technique also

Fig. 131.1 (A–E) DMEK injectors. Multiple closed-system injectors have been used to deliver the DMEK graft into the eye. To date, there is no FDA-approved DMEK injector system in the US.

A: Viscoject IOL injector and tip (a)

B: The staar microinjector and tip (b)

C: DMEK jones tube and tip (c)

D: Modified AMO emerald IOL injector and tip (d)

E: Alcon B cartridge

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AkintoDSAEKsurgery,therearemultiplewaystoinsertDMEK graft tissue. Whether the injector material is a keycomponent as suggested by Dapena etal.7 or the injectordesignismoreimportantassuggestedbyKimetal.1remainsto be seen. Interestingly, in their small series, Kim etal.foundapostoperativeendothelialcellloss(ECL)of28±16%withanAlconBcartridgeattachedtoasyringeofBSS.ThisfindingcomparesfavorablytotheECLof12–29%foundbyHametal. intheir largerstudyusingaclosed-systemglassinjector.9Thesedata suggest that thedesign featuresofaninjector (e.g. a closed system) may prove more importantthanitsmaterialproperties.Furtherclinicaltrialsandlabora-toryworkwithvitaldyestainingforendothelialdamagewillberequiredtobetterinformthisimportanttopic.

Recipient Preparation

PreparationoftherecipienteyeforsuccessfulDMEKsurgeryinvolves creation of surgical incisions, removal of therecipient’s Descemet membrane and corneal endothelium,constriction of the pupil, and creation of a peripheraliridotomy.

Wound Creation

The authors prefer a temporal approach, in the widestcornealdimension,tohelpensuretheprimaryincisionwillnot interferewithgraft implantation.Thenumberof totalincisionsneededforDMEKsurgeryvariesbasedonsurgicaltechnique.ThemajorityofDMEKsurgeonswillcreatetwoto four paracentesis incisions in addition to the primaryincision.Paracentesisincisionsof1mmarecreatedsuperiorandinferiortothemaintemporalincision.AllwoundsforDMEKshouldbeself-sealing,asthisaidsgreatlyinchamberstabilityandsubsequentpositioningofthegraft.Makingtheincisionsparalleltotheirisplanefacilitatesthecreationofself-sealingparacenteses.It ishelpfultomarktheentrance

Table 131.1 CharacteristicsofvariousDMEKinjectors

Injector Incision Materials needed Unique properties

Viscoject IOL injector 2.4 mm Viscoject IOL injector Need to remove springGraft is loaded like an IOL, not aspirated

Staar Microinjector 3.0 mm Requires viscoelastic Graft is loaded like an IOL, not aspirated

DMEK Jones tube 3.2 mm Gunther Weiss DMEK modified Jones Tube14-French gauge nasogastric tubing3 mL syringe

Glass material may be safer for endothelium3 mL syringe for controlled injection and chamber maintenanceCentral dilation to control fluidics

Modified AMO Emerald One Series injector

2.75 mm AMO Emerald One cartridge1 mL Luer-Lok syringe 14-French gauge nasogastric tubingOptional Safety additions3-way stopcock3 mL Luer-Lok syringe

1 mL syringe for controlled injectionA backup 3-way stopcock valve for removing air bubbles and refilling injector if necessary (useful in leaking wounds)

Alcon B cartridge 2.8 mm 3 mL Luer-Lok syringeVarious adapters to join to a syringe

Can be difficult to create a watertight closed system between the cartridge and the syringe

of the incisions with a surgical marking pen so that theparacentesescanbe locatedandaccessedeasilyduring thesurgicalprocedure.Theinternalopeningoftheparacentesesshould not overlap with the area where the graft will beplaced.Aftertheparacentesisincisionsaremade,theprimaryincision is created.Theprimary incision is sized tofit theinjector chosen by the DMEK surgeon (Table 131.1). Theprimary incision should allow a snug fit with the DMEKinjectorandpreventfluidegress,whichcouldriskflushingthe graft out of the main incision during graft injection.Althougha self-sealing stable incision is ideal, theauthorsrecommend suturing even the smallest main incisions toavoidanypotentiallossofthegraft,air,orgasduringlatermaneuvers.

Endothelium-Descemet membrane resection

Aftercreatingthesurgicalincisions,thediseasedendothelium-Descemet membrane complex (EDM) is stripped from thehost cornea. This step can be accomplished in numerouswaysbut it iswidelyagreed that thecreationofa smoothareaofresectionwithoutresidualDescemetmembrane(DM)orstromalfibrilsisofutmostimportance.10ResidualtagsofDMand stromalfibrilsmayallowfluid to collectbetweenthe graft and the recipient stroma, thereby preventingattachmentofthegraft. Itmayalsoresult inasuboptimalinterface,whichcancompromisethevisualqualityinDMEKpatients.Krusewas thefirst to report a lower rateof graftseparationandsubsequentre-bubblingwhenthegraftdoesnotoverlapwithhostDM.10To avoidoverlap, the areaofstrippingonthehostcorneashouldbeslightlylargerthanthediameterof theplannedDMEKgraft (Fig.131.2).ThisresultsinasmallareaofbareposteriorstromadevoidofanyDMcoverage.Initially,theremaybecornealedemaoverly-ing theuncoveredareas; theedematypically resolvesoverdays toweeks, likely asdonor endothelial cellsmigrate tocover the bare stroma.11 The potential increase in graftattachmentmayresultinalossincelldensityasdonorcells


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to cause miosis. Gentle stroking of the iris surface with ablunt instrument can also be used to augment the mioticeffect; however, this may predispose the patient towardsgreaterintraocularinflammationanddevelopmentofcystoidmacular edema postoperatively. The authors recommendagainst application of carbachol and pilocarpine as theprolonged effect may encourage development of posteriorsynechiae.DuetotheimportanceofasmallpupilinDMEK,somehaveadvocatedforstagedsurgeryonly,andavoidanceofthetripleprocedurewhenvisuallysignificantcataractsarepresentconcurrentlywithendothelialdecompensation.

ForDMEKtripleprocedures,adequatevisualizationofthelensisnecessaryforthecataractsurgeryportionofthecase.TheauthorsavoidpreoperativeNSAIDsandexcludedilatingagentsfromtheirrigatingsolutionasbothprolongdilation.Dilation for the cataract surgery portion of a DMEK tripleprocedure can be achieved with intraocular epinephrinealone,orwithpreoperativeinstillationoftopicalphenyleph-rine 2.5% drops and a topical cycloplegic agent such as asingle drop of mydriacil 0.5%. The authors recommendavoidanceofmorepotenttopicalcycloplegicagents,astheireffectsarenotreadilyreversible.

Thereareseveraladditionalconsiderationswhenperform-ing DMEK surgery in conjunction with cataract surgery.FollowingDMEKsurgerythereisahyperopicshift,likelyduetodeturgesenceof the cornea.Hamet al.have reported ahyperopicshiftof1/3ofadiopteronaverage.13Whenselect-ing an IOL, the authors target mild myopia of −0.5D to−0.75Dtoaccommodatethisshiftandachieveafavorableemmetropic or slightly myopic result in the majority ofpatients. DMEK triple procedures can provide additionalchallenges,especiallyearlyinthesurgeon’slearningcurve.Theintraocularlensisnotfullystabilizedjustafterinsertion,whichcanmaketheprocedurechallenging.Asmallercap-sulorhexiscanhelpkeepthelensimplantfromprolapsingandimprovelensimplantstability.Inahighlymyopiceye,theanterior chamberwillbeconsiderablydeeperafter thecataractportionofthecaseandcancontributetodifficultyunscrollingthegrafttissue.Insuchcases,considerationmaybegiventostagingthesurgeryinsteadofacombinedpro-cedure. Additionally, it is possible to inadvertently fill theentirecapsularbagandanteriorchamberwithairorgasinDMEKtripleprocedures.Shouldthisoccur,alloftheairorgas canbeevacuatedand replacedwithBSSanda smallerbubble left in the anterior chamber at the conclusion ofsurgery.This situationcanbebest avoidedby refilling theeyewithBSSpriortoplacingthefinalairorgasbubble.

Peripheral iridotomy

Pupillary block is a reported complication of all types ofendothelial keratoplasty.14,15 With DSEK surgery, pupillarydilation is often employed to prevent pupillary block.16However,withDMEKsurgery,pupillaryconstrictionisusedduringsurgerytopreventgraftdamage.Pupillaryconstric-tionincreasestheriskofpupillaryblockfromanairorgasbubbleintheanteriorchamber.AspupillarydilationisnotdesiredduringDMEKsurgery,itisofgreatimportancethattherecipienteyehasapatentperipheraliridotomy.Thiscanbeaccomplishedinmanyways.Theauthorsprefertocreatetheperipheral iridotomyas inferior andperipheralon the

migrate to cover areasof bare stroma.A small decrease inendothelialcelldensitymaybeasalienttradeifitisaccom-panied by a lower rate of graft detachment. Regardless ofthe planned area of resection, the authors recommend anopticalzonemarkerorcalipersbeusedtomarktheareaofresection.Thesemarksfacilitateprecisegraftcentrationafterunfolding.

AstableanteriorchamberfacilitatesstrippingoftheEDM.Thisstabilitycanbeaccomplishedwithacohesiveviscoelas-tic, air, or BSS using an anterior chamber maintainer. Theuseofviscoelasticaffordsthemoststableanteriorchamber,butrequiresextrasuppliesincludinganirrigationandaspi-ration unit. Some have raised concerns that viscoelasticdevicesmayimpededonorattachment.12However,acohe-siveviscoelasticfacilitatesgraspingandremovingtheEDMfromtherecipientstromalbed,canbeusedtopreventandcontrolbleeding,andcanalsoberemovedcompletelyfromtheanteriorchamber. Intheauthors’experience,usingairprovidesalessstableanteriorchamberbutimprovesvisual-izationofDMasitisscoredandremoved.Nomatterwhatmethodofsupportisused,ablunttippedinstrumentsuchas a reverse Sinskey hook is used to score a circle in therecipientEDM.Afterestablishingthisinitialbreak,thehostEDM tissue is pulled carefully in toward the center of theeyeandremovedthroughthemainincision.Asmentionedpreviously,greatcaremustbetakentoavoiddisturbingtheunderlying stroma, especially in cases of pseudophakicbullouskeratopathyinwhichthismaneuverismoredifficultcompared to Fuchs endothelial corneal dystrophy. It is ofutmostimportancethatthecohesiveviscoelastic,ifused,isremovedinitsentiretypriortoinsertionofthegraft.

Pupillary modulation

After the recipient EDM is removed, attention is directedtoward pupillary modulation to prepare the eye for graftinsertion.A smallpupil is advantageous inDMEKsurgery.The iris serves to protect the graft from contact with theintraocular lens implant, which can damage the endothe-lium,or the crystalline lens inphakicDMEKcases,whichcan be damaged by intraocular maneuvers. Prior to graftinjection,acetylcholineisinjectedintotheanteriorchamber

Fig. 131.2 Host preparation for DMEK. Note the absence of overlap of graft and the host Descemet membrane.

1- Limbus2- 1 mm paracentesis incisions3- Temporal incision to fit injector4- Well-centered DMEK graft (blue)5- Edge of desmetorrhexis6- Thin rim of bare stroma (orange)

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with trypan blue 0.06% (VisionBlue, Dutch OphthalmicUSA,Exeter,NH)isessentialtoincreasecontrastandmaxi-mize visibility of the graft edges. The authors recommendbetween1and3minutesofgraftimmersionintrypanblueforadequatestaining.Whenthestainedgraftisloadedintoaninjector,adoubleorsinglescrollwillform.Incaseswithadoublescroll,orientationcanoftenbeconfirmedbydirectvisualinspectionandthegraftshouldbeinjectedwiththescrollsfacingup(e.g.facingtheposteriorstroma).Theori-entationofasinglescrollismoredifficulttoascertain,butcan be accomplished by observing the movement of theoverlappingareasofthescrollwhenrotatingthetip.Inthecorrectposition, theoverlappingedgesof thegraftwillbeonthetopofthescrollandwillappeartomoveinthesamedirectionasthetipisrotated(e.g.rotatingthetipclockwisewillresultinrightwardmovementoftheoverlappingarea).Ifthegraftisupsidedown,theoverlappingedgeswillmovein the opposite direction of the tip (e.g. rotating the tipclockwisewill result in leftwardmovementof theoverlap-pingarea).Afterrotatingthetiptopositionthegraftinthecorrect orientation, the tissue is injected into the anteriorchamber.Thisgraftorientationtechniquewasfirstdescribedby Peter Veldman, and named the “Veldman Venn” tech-nique. The overlapping DMEK graft edges are similar inappearancetoaVenndiagram(Fig.131.3).

Kruseetal.describedcreatingthreesemicircularmarksattheedgeofthegraftinanidentifiableorder.17Themarksarecreatedinsuccessionwithasmallroundpunchblade,butthedistancesbetweenthemarksvary.Theorderofthethreemarkschangeswhenlookingfromthecorrectedorientationversustheinvertedposition.Thelossofendothelialcellsinthe marked areas and the potential increase in peripheraldetachmentshaslimiteditsuse.

Recently, eyebankshavebegun toplaceanS-stamponthe stromal side of Descemet membrane when preparingDMEKtissue.SimilartotheorientationmarkingsmadeonthestromaonDSAEKgrafts, the stampprovidesdefinitivegraft orientation regardless of scroll characteristics. TheS-stampremainsvisiblefordaystoweeksafterbeingplacedat the eye bank. One concern is the loss of endothelialcells with this technique from the markings itself andthe additional manipulation required by the ophthalmic

patient’s iris as possible. This ensures that the peripheraliridotomy will be uncovered by gas when the patient sitsupright. A peripheral iridotomy can be created preopera-tivelywithaYAGlaser,butitiscriticaltopassaninstrumentthrough the PI intraoperatively to assure its patency. Aperipheral iridotomy may also be created at the time ofDMEK surgery. The authors prefer to bend the tip of a30-gaugeneedle,thenpassitthroughthepupilbehindtheiris,andscratchdownontopoftheneedlewithaSinskeyhooktoestablishanopening.Theopeningcanbestretchedusingabimanualtechniquetoassureitspatency.ForphakicDMEKcasesinwhichthismaneuvercannotbeperformed,aperipheraliridectomycanbecreatedusingafine-toothedforcepstograsptheperipheral iristhroughafairlyverticalparacentesis incision, and Vannas scissors to resect theperipheral iris tissue. It is important toensure that the iri-dectomyisfullthickness.Ariskofallintraoperativeperiph-eraliridotomytechniquesisbleeding.Techniquesthatuseacohesiveviscoelastictomaintaintheanteriorchambercanbeadvantageousinthissettingasthisdevicecanbeusedtotamponadeanybleedingthatmayoccurduringcreationoftheperipheraliridotomy(Video131.2).

Graft Orientation

Whenseparatedfromthestromalsurface,DMEKgraftstypi-cally scroll with the endothelial cell side facing outwards.Correctgraftorientationoccurswhenthecurlsofthescroll(s)face the posterior stroma. Achieving correct orientationbeforeunfoldingandinflatingtheanteriorchamberisvitalforsuccessfulDMEKsurgery.Dependingonthecharacteris-tics of the scroll and visibility through the host cornea,thistaskcanpresentseveralchallenges.Severaltechniqueshave been described to facilitate and confirm proper graftorientation.

Orientation before insertion

InjectingaDMEKgraftinthecorrectorientationisidealandshouldbeattemptedinallcases.Severalstepscanbetakento aid in confirming graft orientation prior to injection.Before loading into the desired injector, staining the graft

Fig. 131.3 Veldman Venn technique. The movement of the overlapping edges of a DMEK graft stained with trypan blue can be observed to determine orientation prior to insertion.

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rotatedaroundthelimbusandgentletappingofthecorneaisperformed.Theoperatingmicroscopelightisturneddownorcompletelyoff.Thedynamicsofthegraftisobservedandlightreflexesfromgraftfoldsandedgesprovideinformationto assess graft orientation. This technique is particularlyusefulinedematouscorneas.

Theuseof intraoperativeopticalcoherencetomography(iOCT) during DMEK surgery is increasing in popularity.23HandhelddevicesandintegratingtheOCTintotheopera-tivemicroscopehavebeendescribed.High-resolutionimagesfromiOCTprovideveryaccurateanddetailedinformationaboutgraftpositioning (Fig.131.5). Inaddition, iOCTcanbeusedtoevaluategraftattachmenttotheposteriorstroma.While the cost of iOCT is prohibitive inmost settings, itsaccuracy in ascertaining graft orientation and versatilityin obtaining real-time details about graft position andattachmentmakesitauniqueandusefuladjunctforDMEKsurgeons.

Changing orientation after insertion

Ifagraftisinvertedafterinsertion,severalstepscanbeusedtoflipthetissuebacktoitscorrectorientation.First,filltheanteriorchamberwithBSS.Thisdeepeningof theanteriorchamber will provide space for the graft to rotate. Next,move thegraft toward the centerof thepupilwithgentletapping (See Unscrolling and centering section). Finally,throughaparacentesis site,useaburstofBSStocreateaninternalfluidwave to rotate thegraft in thedesireddirec-tion.Forexample,ifthegraftisorientedonitssideakintothe letter “C”, aburstoffluid towards the superior aspectof the “C” will cause the superior edge to move in thedirectionof thefluidwaveandthegraftwill subsequentlyrotatecounterclockwise.While this techniquecanbeusedwiththegraftneartheangle,centeringthegraftanddeepen-ingtheanteriorchambercanfacilitatethistechnique.

Unscrolling and Centering

After achieving proper orientation of the DMEK graft, thesurgeoncanproceedwithasetofunfoldingandcenteringmaneuverstounscrollandpositionthegrafttissuewiththeendotheliumfacingtheiris,incorrectanatomicalconforma-tion.Justasobtainingthecorrectgraftorientationisessentialtopreventinggraftdetachment,unscrolling andcenteringthegraftusingprescribedtechniquesareessentialtomini-mize postoperative stromal edema due to endothelial celltraumatizationduringsurgery,graftdecentration,orboth.

Generally, unfolding of the graft is achieved with theassistanceofBSS,anairbubble,oradeliberatelyshallowedanteriorchamber.Allthreeapproachesmanipulatetheeffec-tiveforceoffluid(liquidorgas)withintheunscrolledgrafttissue, and result in theapplicationof forceperpendiculartotheDMsurfaceoftheunscrolledgrafttoopenupthegraftleaflets. This principle also governs the efficacy of cornealtapping and stroking maneuvers – external compressionforcesappliedtotheanteriorcornealsurfacewithacannula–thatvirtuallyallDMEKsurgeonsuseatsomepointduringsurgery toassistwithgraftunfolding.Eachapproachaimsto eliminate direct contact between the graft tissue andmetal instrumentation to minimize donor endothelial cell

technicians. A recent study conducted at the Devers EyeInstitute compared the rate of ECL in 19 patients whoreceivedDMEKtissuewiththeS-stampwith32patientswhoreceived a standard DMEK graft. At 6 months postopera-tively,equivalentratesofECLwerefoundinbothgroups.18The initial studies arepromising for its safetyandefficacycomparedtopreviousmethodsofascertaininggraftorienta-tion.UseoftheS-stampisincreasingamongsurgeonsandeyebanksthroughouttheUS.

Orientation after insertion

Whenthegraftisinjectedintotheanteriorchamber,graftorientation can change and can be difficult to assess. Anedematoushostcorneaorapoorlystainedgraftcanfurtherimpedevisualizinggraftorientation.

A technique using a cannula in the lumen of a doublescroll to confirm graft orientation has been described.19,20Whenthegraftisorientedcorrectlywiththescrollsfacingup, the tip of the cannula will appear blue when movedtowards the scroll edge because of the overlying stainedgraft. If the graft is positioned upside down (e.g. scrollsfacing down), the tip of the cannula will not changecolor when moved to the edge of the scroll. Coined theMoutsouris sign, this technique is useful, but can alsocausecelllosswithinadvertenttouchofthecannulatotheendothelium(Fig.131.4).

Severalno-touchtechniqueshavebeendescribedtodetectgraftorientation.Burkhartdescribedusingahandheld slitlamptoenhancevisualizationofthescrolls.21Whentheslitbeamisplacedoveracorrectlyorienteddoublescroll (e.g.scrollsfacingup),twoadjacentarcscanbeseen(twoscrolls)withadistantslitbeamconnectingthetwoarcs.Ifthegraftis inverted, only one continuous beam is noted. Agarwaletal.describedtheuseofanendoilluminatororlightprobetoaidingraftorientation.22Typicallyusedinretinalcases,a20-,23-,or25-gaugelightprobeisplacedobliquelyonthecorneal epithelium to enhance visualization. The probe is

Fig. 131.4 Moutouris sign. The instrument is placed on top of the graft and moved side to side. If it disappears under a scroll and looks blue (as in the picture above), correct graft orientation has been confirmed. (Courtesy of Mark A. Terry, MD.)


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Güell etal. have described a systematic approach usingBSSfluidtounfoldthedonorgraft.24 Intheir technique,aGills cannula is connected to an automated irrigation-aspiration system (Constellation, Alcon Laboratories Inc.,FortWorth,Texas).Theinstrumenttipisintroducedthroughthemainincisionaftersuturingitclosed.Continuousirriga-tionissethighat60–100mmHg,buttheactualfluidpres-sure is much lower due to the small caliber of the Gillscannula.Low-pressureirrigationflowisusedbothtocenterthe graft scroll, and to unfold the leaflets. As describedabove,theinstrumenttipisplacedwithintheoverlappinggraft leaflets,and the irrigation isapplied fromwithin thescrolled graft to open the leaflets. As grafts from youngerdonorsaremoretightlyscrolledandunfoldinggenerallyismoredifficult in this setting,higherflowpressures canberequired.Thistechniquecanbecombinedwithinjectionofanairbubblewithinthescrollpriortocompleteunfolding,orwithgentlecannula-assistedcompressionoftheanteriorcornealsurfacewhilelow-flowirrigationisapplied.

damage. Additionally, a shallow chamber frequently ishelpful during the unfolding process, as reduced forceoutsidethegraft leafletswillencouragethegrafttounfoldand the reduced chamber area will help prevent the graftfromrescrolling.Thesebasicprinciplesprovideaconceptualfoundation for the various approaches to unfolding theDMEK graft practiced by surgeons at major DMEK centers(Fig.131.6).

Fluid assisted unscrolling

Short bursts of BSS from a 30-gauge cannula on a syringecanbeused toopen the graft scrolls.With the graft posi-tioned so a cannula tip can be placed within or aimed atthe edge of the scrolled graft, irrigation is applied to thescrolledportion(s)ofthegrafttounfolditsleaflets.Duringthisprocess, a shallowanterior chambercanbehelpful inkeepingthenewlyunfurlededgesof theDMEKgraft fromrescrolling.

Fig. 131.5 Intraoperative OCT. While the surgeon’s view is similar in both photos on the left, iOCT reveals that the graft in the top photo is upside down (scrolls down), while the bottom is in the correct orientation (scrolls up).

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thegrafttocontinuetobeunfoldedandmovedasneededforpropercentering.BSScanbeinjectedintotheinterfacebetweentheDescemetsurfaceofthegraftandtherecipientstroma, as needed, to help center and fully unscroll thedonortissue.Subsequently,acannulacanbeusedtostrokeor tap the anterior corneal surface to help unfolding thegraftedges.25Again,asnotedwithfluid-assistedmaneuvers,ashallowanteriorchamberduringbubble-assistedunscroll-ing is helpful in keeping the edges of DMEK graft fromrecurling.

Tightscrollscanpresentseveralchallengesandtheuseofaircanfacilitateatraumaticunscrollinginthesecases.Thetightscrollcanbepositionedsoacannulatipcanbeplaced

Bubble-assisted unscrolling

Small volumes of air from a 30-gauge cannula on a 1mLsyringecanalsobeusedtoopenthegraft.Althoughthiscanbe achieved in severalways, fundamentally, air is injectedeither above the graft or below the graft to facilitate itsunfolding. In the techniquedescribedbyPrice etal., aftertheedgesofthegraftarepartiallyunscrolledwithirrigatingjetsofBSS,asmallvolumeofaircanbeplacedunderneaththegraft,floatingitupwardsothattheDescemetsurfaceisapposed to the recipient stroma. An initial air bubble ofapproximately0.02mLorlessinjectedbeneaththegraftisusedtosecureitsorientation,yetissmallenoughtoallow

Fig. 131.6 Unfolding and centering a DMEK graft using corneal tapping assisted by a shallow anterior chamber. (A) The graft is positioned in proper orientation, with overlapping edges facing upward. (B, C) The graft is unfolded by tapping on the anterior corneal surface with a 30-gauge cannula. (D–G) The graft is centered, prior to complete unscrolling of the graft, by tapping on the limbus and/or peripheral cornea. (H) Additional corneal taps are used to unfurl the peripheral edges. (I) The DMEK graft is fully unscrolled and properly centered. (Courtesy of the University of Iowa.)

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aspiratedfromtheparacentesisincisionsasoftenasneeded.Additionally, if needed, pressure can be applied at theequatorof theglobeusingadigitora larger-borecannulato displace the lens–iris diaphragm anteriorly and shallowthechamberfurther.

Centering and centration

Surgeonsmayneedtorecenterthegraftseveraltimespriorto injecting the final air bubble. This centration canbe accomplished whether the graft is fully or partiallyunscrolled,as longasa layeroffluid isbathingbothsidesof the graft. In the bubble-assisted techniques, BSS first isinjectedintotheanteriorchamber,eitherintotheinterfacebetween the recipient stroma and DM (if the bubble isbeneaththegraft)orbeneaththegraft tomake itfloatup(ifthebubbleisontopofthegraft).Reducingthevolumeoftheairbubblemayachievethesameeffect.Then,thegraftis repositionby tappingor strokinggentlyontheanteriorcorneal surface, the limbus, or the anterior sclera with acannula, tapping or swiping the graft toward the desiredlocation.Inaddition,slowlimbalindentationfollowedbyarapid release of the indentation can be very effective inmoving a graft towards the direction of the cannula. Forexample, ifagraft isnasallydisplaced, indenting the tem-porallimbuswilldeepenthechambernasally.Aquickreleaseof this indentation will result in an internal fluid wavetraveling temporally that will reposition the graft in thedesired temporal direction. As noted above, a shallowchamberwillaccentuatetheeffectofexternalcompressionforcesandresult ingreatergraftmovementcomparedtoadeepanteriorchamber.

Itisidealforthefinalgraftpositiontobecenteredwithinthe area of stripped DM on the recipient cornea. Tourtasetal.haveshownthattheabsenceofoverlapbetweentheDMEK graft and host Descemet membrane correlates withreduced edge detachments and lower rebubble rates.27Regardlessofthesurgeon’sstrategyforsizingthegraftandperforming the descemetorhexis, it may be of particularimportancetominimizeedgeoverlapattheinferiorquad-rant,asthisedgeisleastprotectedbyairorgastamponadeintheearlypostoperativeperiod.Conversely,gapsofuncov-eredrecipientstromabetweenaslightlydecenteredgraftandhostDMaremoreacceptable.Suchgapswillresultinstromaledema that will generally subside, as donor endotheliumand/orrecipientendothelialcellsmigratetorepopulatetheuncoveredstroma.28Aslongasthecentralcorneaiscovered,slightdecentrationofaDMEKgraftdoesnotseemtoimpactthefinalvisualoutcome.

Graft Tamponade With Air or Sulfur Hexafluoride 20%

Immediately after unscrolling and positioning the DMEKgraft,abubbleofairorsulfurhexafluoride20%isplacedintheanteriorchamber.Thepurposeofthebubbleistomain-tainappositionofthegrafttissuewiththeposteriorstromaofthehost,whilethepumpfunctionrecoversandthegraftcanmaintainitsadherenceinaqueoushumor.Avarietyoftechnicalconsiderationstoavoidcomplicationsofairorgas

within the lumen of the scrolled DMEK graft. A small airbubble is then delivered within the scroll(s) such that thebubblewillbeontopof theDescemetsurfaceof thegraftduringtheunscrollingprocess.20Alternately,aslongasthegraftispositionedwiththescroll(s)facingupward,asmallairbubblecanbeplacedontopofthegrafttissue,sothatwith external applicationof a cannula itbecomes trappedwiththescrolledgraft.External tapsareusedtobegintheunscrollingprocess.Then, external strokeson theanteriorcornealsurfaceareusedtodirectthebubbletounfoldthegraft.AsthebubbleispushedalongtheDMtowardacurlededge of the graft, that edge becomes unscrolled. The airbubbleisenlargedsubsequentlyasneededtohelpfacilitategraftunscrolling,untilthecentralendotheliumoftheDMEKgraft is flattened over the iris surface. Once unscrolling iscomplete,thebubbleontopofthegraft isevacuated,andthegraftcanberecenteredasneededusingcornealtapsontheperipheral cornea, limbus,oranterior sclera ifneeded.Ofnote,asdescribedbyKruse,anairbubblecanbepreloadedin the scrolledDMEKgraft and the tissue is then injectedwiththe“bubbleintheroll”tofacilitateunscrolling.

Intheeventasmalledgeisnotunfoldedcompletely, itispossibletoutilizeanairbubbleequaltoorsmallerthanthe graft diameter to maintain the graft’s position whileunfoldingthecurledgraftedge.Termed“bubblebumping,”the folded edge is submerged in BSS, while the anteriorcorneal surfaceoverlying the foldededge is tappedwithacannula.25Graspingthelimbuswitha0.12forcepsandrotat-ingtheeyetowardtheunscrollededge,toensureitscompletesubmersioninfluid,canbehelpful.

Chamber assisted unscrolling

TappingontheanteriorcorneaofaneyewithaveryshallowanteriorchambercanalsobeusedtoopentheDMEKgraft.NeitherirrigationwithBSSnorinjectionsofairareusedtoassist with unfolding the graft in this technique, firstdescribed by Yoeruek etal.26 After confirming the graft’sorientation and releasing aqueous from the paracentesisincisions,a30-gaugecannulaisusedtotapontheanteriorcornealsurfacetounfoldthegraft.Whetherthegraftleafletsare overlapping (single scroll) or nonoverlapping (doublescroll),typicallytheinitialcornealtapsareappliedcentrallywiththelongaxisofthecannulaparalleltothelongaxisofthe graft. Corneal tapping increases the pressure of fluidtrappedwithintheunscrolledgrafttissue,andredirectsthefluidforceperpendiculartotheDescemetsurfacewithintheunscrolled leaflet(s) to open them. Once one leaflet isopened, a bimanual technique can be used, wherein onecannula applies pressure over the unscrolled graft andanothercannulaisusedtotaptheanteriorcorneatounfoldthecurledgraftedge.Inordertorecenterthegraft(whetherfully or partially unfolded) during the process, a 30-gaugecannula isused to tap the limbusor stroke theperipheralcornea,usuallytowardthedesiredlocation.Externalmaneu-vershavegreatereffect,andresultingreatergraftmovement,inashallowchamberthanafullyformedchamber.

This chamber assisted unscrolling technique requiresthattheanteriorchamberissufficientlyshallowtopreventrescrolling of the tissue. In order to maintain a shallowchamberduringtheunscrollingprocess,fluidisreleasedor


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encompassestheperipheraliridotomyattheendofsurgery.This will ensure free communication of fluid across theperipheral iris. The surgeon should also attend to the cre-ationofasufficientlylargeiridotomytomaintainpatency;stretching the peripheral iris with blunt instruments suchas Sinskey and/or reverse Sinskey hooks can be helpful.Somesurgeonswillutilizetopicaldilatingdrops(phenyleph-rine2.5%andcyclopentolate1%)intraoperatively,typicallyafter the graft is unscrolled and centered, to dilate thepupilandminimizetheriskofdevelopingpupillaryblock.Additionally, some surgeons perform a gas-fluid exchangeaftertheinitialperiodoftamponade,priortoplacementofthefinalbubble, toensurenoairorgas is trappedbehindtheiris.

DMEK detachment

Graft detachment is the most frequent complication ofDMEK and remains a challenge for surgeons performingandconsideringadoptionofthissurgicaltechnique.ReportsfromsurgeonsearlyintheirsurgicalexperiencewithDMEKindicate there is ahigh rateof graftdislocations requiringreinjectionofairtosupportthegraft(a“rebubble”procedure),rangingfrom20%to82%.29–32Assurgeonsgainexperiencethegraftdetachmentdrops,rangingfrom4.4%to14%afterpassageofa“learningcurve”period.30,33,34Thiscomplicationhas prompted surgeons to make additional modificationsto initial graft tamponade strategies. For example,Dapena

tamponade, chiefly pupillary block, are employed duringandsometimesbeforesurgery.

Toinstilltheairorgasbubbleoncethegraftisunscrolled,thesurgeonslidesasmallborecannulaorneedle(typically30-gauge)alongtheanterioririsbeneaththegrafttissue.Thechamber volume typically is low at this point. Once thecannula tip is centered beneath the graft in the pupillaryaxis, the surgeon inflates theanterior chamber.The initialbubble can be small or large, depending on the surgeon’sneeds.Ultimately,oncethegraftispositioned,thebubbleisenlargedtooccupynearlytheentireanteriorchamber(Fig.131.7).Somesurgeonswillinsufflatethechambertoahigherintraocular pressure and use a second instrument to com-press thecorneaexternallyandevacuateanyfluidtrappedbetween the thin DMEK graft and the recipient cornealstroma. After a period of time, typically 10 minutes, thebubbleisreducedto80–90%oftheanteriorchambervolumesothatitencompassestheentiregraft.

The primary complication of air or gas tamponade ispupillaryblock.Pupillaryblockcanoccurwhentheanteriorchamberisoverfilledwithairorgasandcausesimpedanceofaqueousflowfromtheposteriorchamberacrossthepupil-larymarginandintotheanteriorchamber.Topreventthispotentiallyblindingcomplication,aperipheraliridotomyinthe inferior iris is created prior to insertion of the graft,eitherintraoperativelyorpreoperatively(seesectiononhostpreparation).Careshouldbetakentoensurethatacuffofaqueousispresent intheperipheralanteriorchamberthat

Fig. 131.7 Graft tamponade with air or sulfur hexafluoride 20%. After the 30-G cannula tip is centered beneath the graft, a slow, controlled inflation of the anterior chamber is performed. Rapid inflation or inflating prior to centering the cannula tip can move and dislodge the graft. (Courtesy of the University of Iowa.)

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especially inthesuperiorcornealendothelium.Thatstudycould not control for positioning, and unlike in humans,both air and SF6 exposed groups demonstrated substantialintraocularinflammationbeginningonday1.48Takenalto-gether,theliteraturesuggeststhatSF6appearstobeastoxictothecornealendotheliumasair,andthatsequestrationofthe corneal endothelium from nutrients in aqueous likelycontributestocelldamageandcellloss.47Repositioningandnormal patient movement should help ensure that thecorneal endothelium is exposed to aqueous and mitigatepossibledamage.

Positioningstrategiestomaintainsupportoftheairorgastamponadeinthepostoperativeperiodvarysubstantially.Acommonpracticeisforthepatienttobeinstructedtomain-tainasupinepositionfor45to60minutesaftersurgeryinthe postoperative unit. Some surgeons will recheck thepatientatthattimetoensureappropriateintraocularpres-sure and perform an air-fluid exchange routinely or asneeded.49,50 The authors currently keep the patient’s eyeshielded and do not examine the patient until the firstpostoperative visit the following day. Patients are ofteninstructed to maintain supine positioning for some timepostoperatively,rangingfromaslittleas24hourspostopera-tivelytoasmuchasevery2hoursforupto1weekpostop-eratively, with practices again varying from surgeon tosurgeon. The postoperative positioning regimen describedbyGüell–inwhichpatientsareaskedtopositiontheirheadinvariouspositionsfor15minuteintervalswhileawakeforthefirstweekpostoperatively–demonstratestheconceptofusing the bubble to tamponade the entirety of the graftsurface.51 While the bubble is still present in the anteriorchamber,shouldanedgeliftpresent,thepatient’sheadcanbepositionedsuchthatthebubblecanbedirectedtowardtheareaof concern (e.g.with theheadhangingbackwardslightlytotamponadeaninferioredgelift).

References1. KimEC,BonfadiniG,ToddL,etal. Simple, inexpensive,andeffective

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etal. attribute their reducedgraftdislocation rate, inpart,to an increase in the duration of complete air fill postop-eratively, from 30 minutes to 45–60 minutes.30 However,it is important to note that the centers most experiencedwithDMEKhaveusedroomairasthetamponadeagent.Inorder to reduce the risk of graft detachment and need forrebubbleprocedures,othercentershaveadoptedtheuseofsulfurhexafluoride(SF6)ata20%concentration,ratherthanroomair, to increase thedurationof thebubble andgrafttamponadeintheearlypostoperativeperiod.DetachmentsafterDMEKtendtostartwithliftingofagraftedge–oftentheinferioredge–andcanbeobservedasearlyasthefirstpostoperativeday.Becauseedgeliftscanprogressoverdaystoweeks toa completedislocationof thegraft, increasingthe duration of the anterior chamber bubble in the earlypostoperativeperiodisadvantageous.

Longer lastinggaseshavebeenattractivealternatives toairtosupportandachievetissuetamponade.SF6,firstsyn-thesizedin1902,isaninert,inorganic,water-insolublegasfirstdescribedintheophthalmicliteratureforuseinretinaldetachmentrepairbyNortonin1973.35Itisusedroutinelyinmodernretinaldetachmentandmacularholesurgeries.36Vitreoretinal surgeons successfully utilize SF6 at a non-expansileconcentrationof20%,37whicheffectivelydoublestheperiodofpostoperative tamponadecomparedtoair invitreoretinal surgery.38 SF6 was first described for use inanteriorsegmentsurgeryin1987,intherepairofDescemetdetachments after cataract surgery, and has since beenreportedonextensivelyforthis indication.39,40SF6hasalsobeendescribedforthetreatmentofacutehydropsinkera-toconus as well as complex DSAEK surgery. Most recently,Güelletal.havereportedontheuseofSF620%fortheinitialgrafttamponadeintheirinitialseriesof15casesofDMEK.Theyreportgoodresultantcornealclarity,meanECLcom-parabletoothergroups,andrateofrebubbleof6.6%.24TheauthorsroutinelyuseSF620%astheinitialagenttoachievegraft tamponade,withsimilar resultsas reportedbyGüell.Whentheanteriorchamberisfilledto80–90%,anairbubblelastsapproximately3–5days,whileaSF620%bubble lastsapproximately 6–10 days. It is vital that a concentrationgreaterthan20%isnotusedasthiswillresultinanexpansilegasthatcanleadtopupillaryblockdespiteplacementofaperipheraliridotomy.

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Surgical Technique for DMEK - Mosby · Keratoplasty. Section 6. Endothelial Keratoplasty. Chapter . 131. Surgical Technique for DMEK. Kevin J. Shah, Michael D. Straiko, Mark A. Greiner.

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