Special cases-2 Lecture -7 Mutez Gharaibeh,MD Colour deficiencies Cones are of three types : 1- Max sensitivity to red 2- Max sensitivity to green 3- Max sensitivity to blue Defects Dichromatism : one of the photopigments is missing. Anomalous trichromatism: abnormal photopigment which differs in sensitivity from the corresponding normal pigment is present. Types Protan defects : long wave photopigment is either missing or abnormal, leading to loss of sensitivity to red light. Deutan defects : Medium wave photopigment is either missing or abnormal, leading to loss of sensitivity to red light. Tritan defects :short wave photopigment is either missing or abnormal, leading to loss of sensitivity to red light. Protanopia Patients see only two hues (blue and yellow) and are almost blind to red radiation. Deuteranopia Deuteranopes see green light as brightly as anyone with normal vision. Rather, they confuse reds with greens. All long wavelengths look yellowish and short wavelengths bluish. Anomalous trichromats perceive colors in the green-red region, but color saturation is weakened. Severity of color discrimination deficits varies widely. Some deuteranomalous persons are not aware of their color vision deficits, while others have color vision deficits that are close to those of dichromats. Most individuals with protanomalous and deuteranomalous color vision defects (i.e., anomalous trichromats) have no problems in naming colors. Type M F Protanopia 1%0.01% Protanomalous 1% 0.03% trichromatism Deutranopia 1%0.01% Deuteranomalous 5%0.35% trichromatism Protan and Deutan defects X chromosome. Tritan defects . Chromosome 7. Table 10.2 page 214 Nl deuteranopia tritanopia Nl deuteranopia protanopia Nl Protanopia Tritanope Protanope < 4 yr Objectively --- method of choice is preferential looking. Subjectively > 3 yr of age. Fletcher-Hamblin Simplified Colour Vision Test The child points to the different color,or select the color which most looks like a reference color. Done under tungsten lightening. 4-7 yr old Ishihara test for unlettered persons is the most effective test for this age group. Screening Pseudoisochromatic designs Grading Farnsworth D15 test 100 hue test Diagnosis----Anomaloscope Occupations in which color deficiency may be handicap Bacteriology/ histopathology Botany Interior design Geology .etc