眼视光--精品医学ppt课件

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1、OcularRefractionandaccommodationBasicconceptofrefractionEssentialcharacteroflight:ElectromagneticwaveAbsorbreflectionrefractionThecontents:BasicconceptofrefractionTheturningorbendingofanywave,suchasalightorsoundwave,whenitpassesfromonemediumintoanotherofdifferentdensity.Thecontents:Ocularrefraction

2、Theabilityoftheeyetobendlightsothatanimageisfocusedontheretina.Thecontents:FocallengthThedistancefromthesurfaceofalensormirrortoitsfocalpoint.Thecontents:Diopter(D)Thediopterisameasureoflenspowerderivedfromthealgebraicmethodofopticalcalculations.Itisdefinedasthereciprocalofthefocallengthofalensinai

3、rmeasuredinmeters.D=1/f(m)orD=100/f(cm)InordertoanalyzetheImageandCalculationofeyeconveniently,weusuallyuseGullstrandsimplifiedeye(orschematiceyeofGullstrand).GullstrandsimplifiedeyeInthereducedschematiceye,thecorneaisassumedtobetheonlyrefractingsurface,theprincipalplane(H)beingplacedatitsapexandas

4、inglenodalpoint(n)atitscenterofcurvature.GullstrandsimplifiedeyeTheglobehasanaxiallengthof22.5mm,andtherefractiveindexoftheeyeissaidtobe1.33.GullstrandsimplifiedeyeTheprimaryfocalpoint(F)isthatpointalongtheopticalaxiswhereanobjectmustbeplacedtoformanimageatinfinity.GullstrandsimplifiedeyeTheseconda

5、ryfocalpoint(F’)isthatpointalongtheopticalaxiswhereparallelincidentraysarebroughttoafocus.FFOcularrefractionRefractivesystemofeyeCornea43DaqueoushumorLens19DVitreousbodyTotalrefractivepowerofeye58.64D70.57DOcularaccommodationAccommodationTheeyechangesrefractivepowertofocusonnearobjectsbyaprocesscal

6、ledaccommodation.Studyhasshownthataccommodationresultsfromchangesinthecrystallinelens.Contractionoftheciliarymuscleresultinthickeningandincreasedcurvatureofthelens,probablyduetorelaxationofthelenscapsule.ThemechanismofaccommodationAccommdatelensUnaccommdatelensAge(years)Meanaccommodation(Diopters)8

7、13.8259.9357.3405.8453.6501.9551.3RefractiveerrorEmmetropiaAbsenceofrefractiveerrorAmetropiaPresenceofrefractiveerrorClassificationMyopia(shortsight)Hyperopia(longsight)AstigmatismAnisometropiaMyopiaDefinit