CONE-SPECIFIC MEASURES OF HUMAN COLOR-VISION

Purpose. To describe a new test of color vision (cone-specific contras t sensitivity) and to evaluate its sensitivity in comparison to standa rd clinical tests. Methods. Cone-specific colored letter charts were g enerated by computer and displayed on a color monitor. Each chart cons ists of colored letters that are most visible at the top but that grad ually fade into a gray background. Cone contrast varies systematically on each chart so that letters are visible to only one cone type (L, M , or S cone). Cone-specific letter contrast sensitivity was measured i n 30 color normals and 13 subjects with hereditary color deficiency. V alues were compared to standard measures of color vision. Results. In color normals, mean log contrast sensitivity was approximately the sam e on L-cone (1.84 +/- 0.08 log contrast sensitivity) and M-cone (1.87 +/- 0.08) tests but tvas reduced on the Scene test (0.89 +/- 0.15) bec ause of the fewer number of S cones in the human retina. Subjects with red color deficiency showed significantly reduced contrast sensitivit y on the L-cone test but normal performance on M- and Scene tests. Sub jects with green color deficiency showed decreased contrast sensitivit y limited to the M-cone test When standardized relative to variability , cone contrast sensitivity identified color deficiency unequivocally in all subjects, whereas FM 100 hue error scores detected 9 of 13 subj ects with color deficiency. Conclusions. Cone-specific contrast sensit ivity provides a quantitative measure of normal color vision and indic ates both type and severity of color deficiency. It is useful for diag nosing hereditary color deficiency and for monitoring early color visi on loss in ocular and systemic disease.