Impact of aging and age-related maculopathy on activation of the a-wave of the rod-mediated electroretinogram.

Abstract

To examine the impact of aging and age-related maculopathy (ARM) on the activation of phototransduction in rod photoreceptors by measuring the a-wave of the flash, full-field electroretinogram (ERG). Enrollees consisted of older adults (> or = 60 years of age) in normal retinal health (n = 41) and those with early (n = 39) or late ARM (n = 7), in whom disease presence and severity were defined based on grading of stereoscopic color fundus photographs according to the Wisconsin Age-Related Maculopathy grading system. Young adults (ages 16-30 years; n = 27) were enrolled for comparison purposes. Previously established procedures were used to estimate the ERG response to two families of flash intensities. By computer subtraction of responses, the isolated rod response was identified. Each participant's ensemble rod responses were fit with the following equation to describe the response (R) as function of flash intensity (I), and time (t): R(I,t) = [1 - exp[-I x S x (t - td)2]] x RmP3, where S is sensitivity, td is the delay before onset of the a-wave, and Rm(P3) is the maximum amplitude. In analyses of older adults, there was no impact of early ARM presence or severity on log S, Rm(P3), or td after adjustment for age and intraocular lens presence. Differences between young and old normal subjects in log S, RmP3, and td disappeared when analyses were limited to older adults with intraocular lenses. When the light absorption of the aged lens is taken into account and reliable definitions of normal retinal aging and ARM are used, the activation of the a-wave as measured by the rod-mediated full-field ERG is not affected by early ARM, nor is it impacted by normal retinal aging.