Color discrimination in heterozygous deutan carriers

Purpose. The color discrimination abilities of heterozygous deutan female c arriers were measured using color mixture thresholds and compared with thos e of suspected nonheterozygous normal subjects. Methods. Eight test subject s and 26 control subjects were run on a computer-controlled color test (col or mixture thresholds) that presented 1 degrees diameter spots on a color t elevision monitor for 1/60 of a second. A QUEST procedure was used to deter mine visual thresholds for spots varying in brightness and/or color. Indivi dual data points were graphed on an X/Y plot and fitted with an ellipse. Th e major and minor diameters of the ellipse represent the color and brightne ss thresholds, respectively. Results. The mean axis angle of the ellipse fo r the heterozygous carriers did not differ from that for the controls (15.7 5 degrees vs. 14.93 degrees, p = 0.428, Mann-Whitney test). The carriers di d show, however, a larger mean major axis length (68.79 vs. 46.78, p = 0.02 18, Mann-Whitney test). Additionally, the length-to-width ratios for the ca rriers were higher than the controls (9.34 vs. 6.80, p = 0.0403, Mann-Whitn ey test). Conclusions. Deutan-carriers do show reduced color purity discrim ination as measured using color mixture thresholds compared with nonheteroz ygous, color vision normals.