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Color vision defect
 

Color vision defect

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    Color vision defect Color vision defect Presentation Transcript

    • Defective Color VisionGauri S. Shrestha, M.Optom, FIACLE
    • Color Vision Deficiencies Monochromacy Only one Pigment Type is present Dichromacy Only two Pigment Types are present Trichromacy All three Pigment Types are present
    • Monochromacy-Shades of Gray 3 Types Rod Monochromats • Most Common Type: 10 in 1 million people • No cones, very poor visual acuity Blue Cone Monochromats • Colorblind in photopic and scotopic conditions • Narrow range of mesopic conditions that they are not colorblind Cone Monochromats • Rarest Type: Only 1 in 100 million people • Acuity is fine during photopic conditions Patients learn to label colors by other cues
    • Monochromats These patients can match any wavelength in the spectrum by changing the intensity of another wavelength Termed: COLOR BLIND Poor Visual Acuity Sunglasses are a must! Depending on rod system for vision
    • Monochromacy10/1,000,000 - rod vision only Only see shades of lightness S M L Also poor visual acuity ROD 70 0
    • Dichromacy-2 Pigment Types More common than Monochromacy 3 Types Protanopia-Missing long wavelength (red) pigment Deuteranopia-Missing middle wavelength (green) pigment Tritanopia-Missing blue pigment
    • Dichromacy• Protonopia S+ L+M+S+ L+ – No L cone; X linked L-M- L-M-S- M- – 1% males, 0.02% females• Deuteranopia S M L – No M cone; X linked – 1% males, 0.01 %females• Tritanopia – No S cone; Autosomal dominant – 0.002% males, 0.001% females
    • Neutral Points The wavelength where the two remaining pigments cross Colors look very desaturated and whitish Patients cannot distinguish colors in this area of the spectrum • Colors at this wavelength are perceived as gray
    • Dichromatic Neutral Points
    • Trichromacy-3 Pigment Types There is no ‘neutral point’ 3 Types Protanomaly-shifted red pigment Deuteronomaly-shifted green pigment Tritanomoly-shifted blue pigment
    • Anomalous Trichromat• L&M pigment spectra shifted closer together S M L Match colors differently from ROD normal trichromats Some colors less discriminable 70 0
    • Hereditary Color Vision DefectsDEFECT PREV. IN MALES TRANSMISSIONDeuteronopia 1% X-linked recessiveProtonopia 1% X-linked recessiveDeuteronomaly 5% (Most Common) X-linked recessiveProtonomaly 1% X-linked recessiveTritanopia & .005% (Most Rare) Autosomaltritanomaly Dominant
    • Replacement model of Dichromacy Missing photopigment is replaced by a remaining photopigment Deuteranope: chlorolabe is replaced by erythrolabe Protanope: missing erythrolabe is replaced by chololabe Exception: missing cynolabe is not replaced by another photopigment
    • M-cone displaced toward L-cone displaced towardlong wavelengths short wavelengths
    • Spectral sensitivity: ChromaticSystem Presentation: Large stimuli (1°) and long duration (200msec) background moderately bright (1000 trolands)
    • 440 520 620nm nm nm
    • Spectral sensitivity: LuminanceFunction 660nm
    • Wavelength Discrimination Wavelength discrimination= absent Color discrimination= 545 luminance profile 490
    • Wavelength Discrimination Wavelength discrimination at longer wavelength Poor wavelength discrimination at 495nm
    • Color confusion lines Green=reddish purple Essential monochromat above 545nm
    • Color confusion lines Red-green confusion Essential monochromat above 545nm
    • Color confusion lines Confusion b/w Blue- violet & yellow
    • Saturation Neutral point: desaturated appearance of spectral stimuli at specific wavelength 570nm
    • Saturation
    • Color labeling 4 9 5 9 0 0 Color labeling is remarkably good in color vision deficiency However, Industrial color labeling is difficult, such as stripe/pattern analysis
    • Color Vision and Females Tend to be carriers Tend to have normal color vision 20 times less likely to have a color vision deficiency
    • Transmission of X linked, red-greendefects from parents to offspring X X X X X XX XX  X X Y XY XY Y XY XY Father Normal (XY) Father Defective ( Y) Mother Normal (XX) Mother Normal (XX)
    • Transmission of X linked, red-greendefects from parents to offspring    X X X X   X Y Y Y Y Y XY Father Normal (XY) Father Defective ( Y) Mother defective ( ) Mother Normal ( X)
    • Transmission of X linked, red-greendefects from parents to offspring  X X X XX Y Y XY Father Normal (XY) Mother carrier ( X)
    • Congenital vs. Acquired CONGENITAL ACQUIREDAffects both eyes equally One eye only OR asymmetricUsually a R-G defect B-Y OR R-GOther visual functions normal Other visual functions abnormalStable through lifetime Variable, dependant on test and diseases conditionsLearned to adapt-can label Cannot name color correctlyobjects
    • Congenital vs. Acquired CONGENITAL ACQUIREDMore prevalent in male Equally prevalent in male and femaleNot associated diseases or Classification nottoxicity straightforward with standard clinical color test
    • Kollner’s Rule Outer retinal diseases and media changes result in blue- yellow color vision defects Inner retina, optic nerve visual pathways and visual cortex diseases result in red-green defectsLocation Defect conditionMedia B-Y Nuclear sclerosisOuter retina B-Y AMD, DRInner retina R-G Optic atrophy, toxic amblyopiaPathway R-G Lesions
    • Chromatopsia These patients have no trouble distinguishing wavelengths, but perception of colors is altered Similar to wearing a filter over the eyes May occur in patients taking various medications Xanthopsia-slightly yellow tint (Digitalis) Cataract Formation • Patients notice blue tint upon cataract removal
    • We can measure2. the reflectance of an object2. brain responses3. behavioral responsesBut we can only guess whether your sensations are really the same as mine …
    • Kollner’s Rule BE CAREFUL-IT DOESN’T ALWAYS WORK Blue-Yellow Defects Associated with outer-retina problems (diseases that effect the photoreceptors) Ocular Media-Cataracts Red-Green Defects Associated with inner-retina problems (ganglion cells and visual pathways to the brain
    • LOCATION DEFECT CONDITION Media Blue-Yellow Nuclear SclerosisOuter Retina Blue-Yellow ARMD Diabetic RetinopathyInner Retina Red-Green Lebers Optic Pathways Atrophy Toxic AmblyopiaInner Retina Red-Green Lesions Pathways