Abstract

Two methods have been used to describe the changes with light level and age of photopigment kinetics: color matching (which is little influenced by increased scattered light with aging) and retinal densitometry (which is influenced by both pigment optical density and photoreceptor coverage). Using a color matching technique, we have reported that for the foveal cones, the amount of light required to bleach half of the photopigment (halfbleach illuminance) decreases with age after 30 yr, while the optical density of the functioning cones does not.¹ We now report that there is also a significant difference [X²(1), p < 0.005] between observers younger than vs older than 40 yr in the slope of the function of retinal illuminance vs proportion of pigment bleached at equilibrium. These data are inconsistent with a single compartment first-order model in two ways: (1) it cannot account for a slope change and (2) measured slopes, even for the older observers, are much too steep. The difference between age groups does not mimic that of greater vs lesser exposure to light by younger observers, in which there is a change in the slope but not in the half-bleach illuminance. The data are qualitatively similar to retinal densitometry reports of slower regeneration changes with aging.

© 1989 Optical Society of America