Abstract

Following adapting field onset, the amplitude of the cone-system electroretinogram (ERG) b-wave increases systematically over several minutes, a finding that has been assumed to represent a partial return of the ERG response toward the dark-adapted value. To examine the validity of this assumption, we have measured luminance-response functions of the cone-system ERG, isolated using 31-Hz flicker, in normal subjects under both dark-adapted and light-adapted conditions. Our findings show that the increase in amplitude of the cone-system flicker ERG that occurs during light adaptation does not represent a return toward a dark-adapted baseline but, instead, entails a substantial enhancement above the dark-adapted value. It is likely that this is also the case for the single-flash ERG, as evidenced by our findings relating to a subject with an unusual form of night blindness, in whom the absence of rod-mediated vision allowed the recording of single-flash cone system ERG responses in the dark-adapted state. Preliminary evidence suggests that selective alterations in ERG off-components may contribute to this phenomenon.

© 1990 Optical Society of America