Factors that influence the increase in the electroretinogram 30-Hz flicker amplitude during light adaptation

Cone responses of the electroretinogramm (ERG) surprisingly increase during the first few minutes of light adaptation. In this study, especially the influence of rods and cones on this not yet understood phenomenon was examined. In 100 subjects a dark-adapted ERG was recorded. Afterward, two 30-Hz flicker recordings were performed, the first one after 1 min and the second one after 10 min of light adaptation. The relative flicker-amplitude increase was calculated. The influence of the ERG standard rod response and the 30-Hz flicker amplitude itself on the 30-Hz flicker-amplitude increase was estimated. The mean increase in the 30-Hz flicker amplitude was 51.7%. There was no significant correlation between the standard rod amplitude and the amplitude growth (r = 0.031). The correlation between the 30-Hz flicker amplitude itself and the increase in cone response was -0.426 (P < or = 0.001). The lower the cone flicker amplitude was after 1 min of light adaptation, the bigger was the amplitude increase. This might either be due to saturation or indicate that the flicker-amplitude increase is mainly related to cone function rather than being dependent on the rod-response amplitude.