Binocular vision and refractive surgeryWord文件下载.docx

Binocular vision and refractive surgeryWord文件下载.docx

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Binocularstatuscanhaveaneffectontheoutcomeofrefractivesurgery.Someaccommodativedeviationsandanisometropiacanbemanagedeffectively.Fullyaccommodativeesotropiahasbeensuccessfullytreatedinyoungpatientsbuttheoutcomecanbelesspredictableinolderpatients.Highanisometropesareusuallyunaffectedbythechangeinaniseikoniafollowingrefractivesurgerybutthereareexceptions.Failuretorecogniseandappropriatelyclassifyabinocularvisionanomalypre-surgicallycanresultinsymptomsthataredifficulttomanagepost-operatively.Refractivesurgeryproducingabinocularvisionanomalywheretherewasnonepre-operativelyislesscommon.Ipresentareviewoftheliteraturediscussingtherelationshipbetweenbinocularvisionanomaliesandrefractivesurgery,illustratingthefindingswithpublishedreportsofsuccessfulandunsuccessfulbinocularpostoperativeoutcomes.Iarguethatpredictingthebinocularoutcomeshouldbeconsideredpre-operativelyforeveryrefractivesurgerypatient.

Keywords:

Binocularvision;

Refractivesurgery;

Heterophoria;

Heterotropia;

Aniseikonia;

Cyclotorsion

ArticleOutline

1.Refractivesurgeryasatreatmentforabinocularvisionanomaly

1.1.Esotropiaoresophoria

1.1.1.Fullyaccommodativeesotropia

1.1.2.Convergenceexcessesotropia

1.1.3.ConstantEsotropiawithanaccommodativeelement（partiallyaccommodative）

1.1.4.Exotropiaorexophoria

1.1.5.Aniseikonia

2.Apre-existingbinocularvisionanomalyaffectingtheresultsofrefractivesurgery

2.1.Torsion

3.RefractivesurgerycausingaBVproblem

4.ExacerbatingaBVproblem

4.1.Comitantheterophoria

4.1.1.Esophoria

4.1.2.Exophoria

4.1.3.Verticaldeviations

4.2.Aswitchinoculardominance

4.3.Monovision

5.Comitantheterotropia

5.1.Aconstantdeviation

5.2.Anintermittentdeviation

6.Incomitantdeviation

6.1.Constant

6.2.Intermittent

6.3.Monovision

6.4.Torsion

6.5.Binoculardiplopiapost-refractivesurgery

7.Pre-operativeassessmentofrefractivesurgerypatients

8.Summary

References

Therelationshipbetweenametropiaandbinocularsinglevisioncanbecriticaltothesuccessful,asymptomaticoutcomeofanyrefractivecorrection,whetheritisanexternalapplianceorsurgery.Relativelysmallmodificationstoarefractioncanresolveproblemswithbinocularsinglevisionforsome,whereasitcancreateproblemsforothers.Forthemajorityofpatientsthebinocularapparatusisrobustenoughtocopewithchangestotherefractivestatusbutthisisnottrueforeverybody.Reliefofsymptomscanbedifficultwhenachangeincorrectionaffectsbinocularcomfort.Withspectaclesandcontactlensessimilarconsiderationsapply[1]butsubsequentmodificationofthecorrectionismucheasierwiththeseformsofrefractivecorrectionthanfollowingrefractivesurgery.Inpatientswithanunderlyingbinocularconditionitwouldbeanadvantagetobeonestepaheadofthesituationbyhavingafullpre-operativeassessmentofthebinocularstatus,asinthesecasestheaccuracyofthecorrectioncanbecritical.

1.Refractivesurgeryasatreatmentforabinocularvisionanomaly

1.1.Esotropiaoresophoria

Aconvergentdeviationofthevisualaxesmayormaynotbeassociatedwitharefractiveerror.Thetermaccommodativeesotropiareferstoagroupofmanifestdeviationsthatareaffectedbytheaccommodativestatusofthepatient;

thedeviationwillbereducedbyahypermetropiccorrectionorexacerbatedbyamyopiccorrection.

1.1.1.Fullyaccommodativeesotropia

Hypermetropesthathaveaconvergentdeviationwithouttheirrefractivecorrection,butbinocularsinglevisionwhenfullycorrected.

Thespecificsofthedefinitioncanvaryslightly.

1.Afullyaccommodativeesodeviationisorthophoricwithglassesandeitheresophoricoresotropicwithoutglasses.

2.Afullyaccommodativeesotropiahasbinocularsinglevisionwithglasses（orthophoriaorheterophoria）buthasamanifestesotropiawithoutglasses.ThisisthedefinitionusedinUK.

Intheory,anoptimalhypermetropiccorrectionshouldproduceanasymptomaticbinocularresponse,whetherthecorrectionisviaspectacles,contactlensesorrefractivesurgery,andindeedDvalietal.[2]achievedabinocularoutcomein21of24hyperopicchildren.Surprisinglythisdoesnotalwaysappeartobethecase.Logicwouldsuggestthatinapresbyope,whonolongerhasanymeasurableaccommodation,theangleofdeviationwoulddependlittleontherefractivecorrection.Practicalexperiencedoesnotnecessarilysupportthisprediction,withpresbyopessometimesremainingesotropicwithouttheirglassesandhavingbinocularsinglevisionwiththeircorrection.Guntonetal.[3]reportedsuchacase,a68-year-old.Pre-operativelythemeansphericalcorrectionwasR+7.50L+8.50add+2.50.Esophoricwithhisprescriptionandesotropicwithout.Followingcataractsurgery,withanimplantcorrectinghisrefractiveerror,hispost-operativemeansphericalprescriptionwasRplanoL+0.50butwitha25Δesotropiathatlaterneededcorrectingwithasquintoperation.

1.1.2.Convergenceexcessesotropia

Definedasanaccommodativeesotropiawithahighaccommodativeconvergencetoaccommodation（AC/A）ratio.Inpractice,thisreferstoagroupofpatientswhoarenormallybutnotinvariablymildlyhypermetropic.Whenwearingtheiroptimaldistancecorrectiontheyarebinocularfordistancefixation.Whenevertheyaccommodatetheybecomeesotropic.Mostcommonlytheesotropiaisonlydetectableonnearfixationwhenviewingadetailedtarget.Iftheneedforaccommodationisremoved,byusinga+3.00DSadditionontopoftheirfulldistanceprescription,thenviewingatargetat33 

cmtheymaintainbinocularsinglevision.Notall‘nearesotropias’aresoinfluencedbyaccommodationbutwhentheyare,refractivesurgerywillnotaffecttheAC/Aratio.Thesepatientsareunlikelytohaveafullbinocularoutcomewithouttheuseofan‘add’orsubsequentsquintsurgery.

1.1.3.ConstantEsotropiawithanaccommodativeelement（partiallyaccommodative）

Thedefinitionofapartiallyaccommodativeesotropiacanvary.

1.Anesodeviationisretainedwiththefullhypermetropicdeviation,butbecomeslargerwithoutthecorrection.Thisdeviationmaybeesophoricoresotropic.

2.InUKthetermhasbeensupersededbythemorelongwindedbutdescriptive‘constantesotropiawithanaccommodativeelement’.Itreferstoesotropiaforalldistancesoffixationbothwithandwithoutcorrection,buttheangleofdeviationisreducedwhenthehypermetropiaiscorrected.

Thesedifferencesinclassificationmayseemsubtlebuttheymakeinterpretationoftheliteraturedifficult.Stidhametal.[4]claimedthatthepost-refractivesurgeryoutcomeofanaccommodativestrabismuscouldnotbepredictedbythepre-surgicalclassificationofthedeviation,notingachangeintheeso-deviationinonly42%of24hypermetropicpatients（meanrefractiveerrorpre-op+7.25;

post-op+2.25）,whereasNemetetal.[5]hadasuccessfuloutcomeinsixoutofsixpatients,threefullyaccommodativeandthreepartiallyaccommodative.

1.1.4.Exotropiaorexophoria

Definedasanoutwarddeviationofthevisualaxes,thelinkwiththerefractivestatusisnotasclearaswithesodeviations.Adivergentdeviationwillnormallybeexacerbatedbyahypermetropiccorrectionandreducedwhenaccommodationisstimulatedusingconcavelenses.Myopesoftenhaveanincreasedexodeviationwhentheyviewaneartargetwithouttheircorrection.Nemetetal.[5]successfullycorrectedtwocasesofexotropiausingrefractivesurgeryforanisomyopia.Overcorrectingamyopewillstimulateaccommodationforallfixationdistancesbyeffectivelyrenderingthepatientslightlyhypermetropic.Thiscanreducesymptomsinadecompensatingexophoriabutthepermanenceofrefractivesurgerymakesthelong-termvalueofthisquestionable,particularlywhenthepatientapproachespresbyopia.

Thenormallimitofthevisualsystemforfusingimagesofdifferentsizeisaninter-oculardifferenceinperceivedsizeof3–5%[6]and[7].Retinalimagesizewillvarywithrefractiveerror,dependingonitsaetiologyandmodeofcorrectionbutitistheperceivedimagesizenottheretinalimagesizethatresultsinaniseikoniaandthetwoarenotnecessarilythesame[8].Asaroughguide,Isuggestthatthelikelihoodofaniseikoniainfluencingbinocularcomfortshouldbeconsideredwhenanisometropiaisgreaterthan4.00DS.

Spectaclecorrectionofhighanisometropiacarriesproblemsintermsoftheappearanceandfittingofasymmetricalspectaclelenses,specificallyintermsoftheirthicknessandthemagnificationfactor.Refractivesurgerywillresolvetheseparticularissuesandtherearereportsofsuccessinbothadultpatients[5]andchildren[9]and[10].Thisputstheadvantageofrefractivesurgerytothecosmesisofanisometropiabeyonddisputebuttheeffectonaniseikoniaisnotsostraightforwards.

Axialanisometropiaisthetermusedtodescribeaninter-oculardifferenceinrefractiveerrorduetodifferencesinthelengthofeachglobealongthevisualaxis,therefractingpowerofeacheyebeingidentical.ThesimpleillustrationinFig.1showsthatthemoremyopiceye,whichwillbelonger,willhavealargerretinalimagesize.

Fig.1. 

Theeffectofglobelengthonretinalimagesize.Inbothillustrationsthetargetarrowisthesamesize.Thesmallereye（A）hasasmallerretinalimagethanthelongereye（B）.

F