We used a noninvasive technique to investigate changes in photoreceptor function with aging in observers 13-69 years of age. This technique, steady-state color matching, provides estimates of the optical density of cone photopigments, the illuminance that bleaches half of the photopigment, and the ratio of the primaries required at moderate light levels. In normal human retinas, we found that the optical density for a 4-deg field is affected minimally by aging from the second through the seventh decades. The average optical density is 0.27 ± 0.054. The optical densities of older observers varied more than those of younger observers. The change in optical density with age is nonmonotonic, with slightly lower values for the youngest and oldest observers in our study. The retinal illuminance that bleaches half of the cone photopigment varied little across observers, averaging 4.37 log Td ± 0.119. The change with age, which averages 0.00018 log Td per year over all observers, also is nonmonotonic. Moderate illuminance color matches did change with age, as expected, with a monotonic decrease with age in the ratio of the long-wavelength primary to the short-wavelength primary required for the color match.

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.