Contrast sensitivity-luminance function in aging

Abstract

We have previously reported (ARVO, 1987) that senile miosis cannot account for age-related deficits in spatial contrast sensitivity over a three-log unit range of luminance. Although the participants were free from significant media opacity, the possibility remains that their deficits could be due to differences in retinal illuminance between young and older observers. If a difference in retinal illuminance accounted for the age differences in contrast sensitivity, functions plotting sensitivity against luminance should be superimposable by a shift parallel to the luminance axis. In the present study we measured spatial contrast sensitivity under a range of luminance levels in young and old adults who were free from identifiable eye disease. Contrast thresholds for sinusoidal gratings (0.5, 2, 4, 8 cycles/deg) were measured over a three-log unit range of luminance (0.1-107 cd/m2), sampled at 0.5-log unit intervals. The contrast sensitivity–luminance functions changed as a function of test spatial frequency for both age groups. The functions at all spatial frequencies were parallel for the two age groups and could be superimposed by a vertical shift along the sensitivity axis and not by a lateral shift along the luminance axis. These data suggest that the age-related deficits in spatial contrast sensitivity are not the simple consequence of reductions in retinal illuminance produced by either senile miosis or increased light absorption by the ocular media.