Age-related changes in color discrimination near the achromatic point

Purpose. Age-related increases in ocular media density reduce the short-wavelength content of broadband lights. The visual system partially compensates for density increases to maintain color appearance (Kraft and Werner, Vis. Res. Suppl., 1995), but compensation would not be expected to function for color discrimination because small differences are presumably reduced below the noise intrinsic to the visual system. Color discrimination thresholds were measured in observers of widely varying ages to determine how the perception of desaturated lights changes with age. Methods. 21 color-normal observers (11 younger observers - average age: 30 years, and 10 older observers - average age: 74 years) participated in a two-alternative-forced-choice procedure using a 2-down/1-up staircase (run for 8 reversals, the final six reversals were averaged to determine threshold). In each trial, two 1.5-second flashes of light (1.2° visual angle) were presented in Maxwellian view with 3 second interstimulus intervals. One of the flashes was a broadband light (x=0.33, y=0.35). The other flash was a mixture of broadband and monochromatic light (8 wavelengths, 420-680 nm). The observer's task was to choose which of the flashes had a chromatic component. Total sensation luminance of the flashes was 250 Trolands. Results. At 420 nm, a wavelength strongly affected by the ocular media, colorimetric purity thresholds for older observers were 0.84 log units higher than thresholds for younger observers. From 460-680 nm, colorimetric purity thresholds for older observers were an average of 0.25 log units (range: 0.14 to 0.36 log units) higher than those for younger observers. Conclusions. Although the visual system partially compensates for increasing ocular media density to maintain the color appearance of broadband lights across the life span, color discrimination becomes progressively worse with increasing age.