Aging and human cone photopigments

Abstract

Previous studies1,2 have disagreed about the effects of aging on human cone optical densities. We have examined the question of whether there are age-related changes in the density and half-bleach illuminance of normal observers. We used a color-matching method to measure the optical density of the photopigments within cones. Forty normal observers between the ages of 12 and 69 were tested. The subjects made color matches for 4° fields at nine retinal illuminances from 260 to 260,000 td. All patients older than 50 had an additional eye exam to insure normal retinas and optic media. The measured optical density changes minimally with age (0.001/yr). The illuminance that bleaches half of the cone photopigment does not show any monotonic change with age. The average half-bleach illuminance is 4.36 log td (s.d. = 0.139); the average optical density for a 4° field is 0.27 (s.d. = 0.07). The current measurements are insensitive to changes in the relative numbers of cones and to moderate changes in the clarity of the optic media. Age-related changes in these measures of photoreceptor function are minimal, although disease-related changes can be large.