Color discrimination in heterozygous deutan carriers

The color discrimination abilities of heterozygous deutan female carriers were measured using color mixture thresholds and compared with those of suspected nonheterozygous normal subjects.

Eight test subjects and 26 control subjects were run on a computer-controlled color test (color mixture thresholds) that presented 1 degree diameter spots on a color television monitor for 1/60 of a second. A QUEST procedure was used to determine visual thresholds for spots varying in brightness and/or color. Individual data points were graphed on an X/Y plot and fitted with an ellipse. The major and minor diameters of the ellipse represent the color and brightness thresholds, respectively.

The mean axis angle of the ellipse for the heterozygous carriers did not differ from that for the controls (15.75 degrees vs. 14.93 degrees, p = 0.428, Mann-Whitney test). The carriers did show, however, a larger mean major axis length (68.79 vs. 46.78, p = 0.0218, Mann-Whitney test). Additionally, the length-to-width ratios for the carriers were higher than the controls (9.34 vs. 6.80, p = 0.0403, Mann-Whitney test).

Deutan-carriers do show reduced color purity discrimination as measured using color mixture thresholds compared with nonheterozygous, color vision normals.