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1、RefractiveerrorEmmetropiaAdequatecorrelationbetweenaxiallengthandrefractivepowerParallellightraysfallontheretina(noaccommodation)Ametropia(Refractiveerror)MismatchbetweenaxiallengthandrefractivepowerParallellightraysdon’tfallontheretina(noaccommodation)Nearsightedness(Myopia)Farsightedness(Hyp
2、eropia)AstigmatismPresbyopiaAccommodationEmmetropiceyeobjectcloserthan6Msenddivergentlightthatfocusbehindretina,adaptativemechanismofeyeisincreaserefractivepowerbyaccommodationHelm-holtztheorycontractionofciliarymuscle-->decreasetensioninzonulefibers-->elasticityoflenscapsulemoldlensintospheri
3、calshape-->greaterdiopticpower-->divergentraysarefocusedonretinacontractionofciliarymuscleissuppliedbyparasympatheticthirdnerveMyopiaParallelraysconvergeatafocalpointanteriortotheretinaEtiology:notclear,geneticfactorCausesexcessivelongglobe(axialmyopia):morecommonexcessiverefractivepower(refra
4、ctivemyopia)MyopiaFormsBenignmyopia(schoolagemyopia)onset10-12years,myopiaincreaseuntilthechildstopsgrowinginheightProgressiveandmalignantmyopiainterchangeablemyopiaincreaserapidlyeachyearandisassociatedwithvitreousopacities,fluidityofvitreousandchorioretinalchangerateofincreaseinamountofmyopi
5、agenerallytapersoffatabout20yearsofageMyopiaCongenitalmyopiaMyopia>10DIncreaseslowlyeachyearMyopiaSpecialforms:nuclearsclerosis,keratoconus,spherophakiaSymptomsBlurreddistancevisionSquintinanattempttoimproveuncorrectedvisualacuitywhengazingintothedistanceHeadacheAmblyopia–uncorrectedmyopia>10D
6、MyopiaMorphologicchangesdeepanteriorchamberatrophyofciliarymusclevitreousmaycollapseprematurely-->opacificationfunduschange:lossofpigmentinRPE,largediscandwhitecrescent-shapedareaontemporalside,RPEatrophyinmaculararea,posteriorstaphyloma,retinaldegeneration-->hole-->increaseriskofRDTreatment:c
7、oncavelenses,clearlensextractionHyperopiaParallelraysconvergeatafocalpointposteriortotheretinaEtiology:notclear,inheritedCausesexcessiveshortglobe(axialhyperopia):morecommoninsufficientrefractivepower(refractivehyperopia)HyperopiaSpecia
