视力与对比敏感度

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1、视力与对比敏感度在白内障中的应用季樱红张斌卢奕Visualangle1circle=360°(degree)1°(degree)=60′(arcminute)1′(arcminute)=60″(arcsecond)Visualangle设计检查距离为５m，视标对眼形成的张角为5分，则视标的高度H为：常规检查距离：美国定为20feet（h’=8.839mm），在欧洲的一些国家定在６m分数20/20，20/40或6/6，6/12小数符号1.0，0.5最小分辨角MAR＝１minarc；MAR＝２minarc；最小分辨角的对数表达(log

2、MAR)：视力是20／20(6／6)时，MAR＝１minarc，则logMAR＝lg1.0＝0.0；视力是20／40(6／12)时，MAR＝2minarc，则lg2.0＝0.30常用的视力记录与计算分数F20/2020/40小数V1.00.5视角(最小分辨角)a=1/F=1/V1’2’最小分辨角的对数表达（LogMAR）=Loga00.3LogV=-Loga0-0.35分制L=5+LogV=5-Loga5.04.7平均视力：一般可采用LogMAR和5分制视力取平均值DefinitionofvisualacuityMinimumdi

3、stinguishable(minimumvisible)MinimumseparableMinimumcognizable(orlegible).Minimumdistinguishable(minimumvisible)ToseesomethingasbeingdistinguishablefromthebackgroundForapointtheexpectedresolutionis10to35secondsofarcForalinemayvaryfrom.44to10secondsdependingonthewidth.

4、LUMINANCEANDCONTRASTAFFECTTHISTYPEOFVAMinimumseparableacuityTodetermineifagroupoftargetsareseparateanddistinct.GratingVernierGrating:aminimumdifferenceof52to64secondsofarcContrastSensitivityFunction(CSF)SpaceFrequency(SF)Contrast=(Lmax-Lmin)/(Lmax+Lmin)ContrastSensiti

5、vity=1/Contrast20/20,1cycle/2’相当于SF=30cycle/degreeContrast=100%SF=6cpdContrast=10%Contrast=50%Contrast=100%SF=18cpdContrast=10%Contrast=50%Contrast=100%100%0%对比度(%)空间频率Vernier:todistinguishbetweentwolinesplacedend-to-endwithonelaterallydisplaced.moresensitive(2to12sec

6、ondsofarc)MinimumcognizableorlegibleTobeabletoseparateanddistinguishforms.(lettersandnumbers)Snellenletter:Snellenacuityisbasedonthetheorythattheminimumangleofresolutionis1minuteofarc.ETDRSOnly10“Sloan”letters(C,O,H,Z,V,S,N,D,K,R)Spacingbetweenlettersisequaltoaletterw

7、idthandbetweenlines,thespacingisequaltoletterheightTheprogressionbetweensuccessivelinesisalogsizedifference儿童视力表PotentialAcuityMeter(PAM)干涉条纹计不同空间频率干涉条纹光栅有垂直、水平、左倾45度、右倾45度4种方向。暗室内,将视网膜计的额托顶在患者前额上,从小到大转动刻度盘Thankyou!