Amplitude increase of the multifocal electroretinogram during light adaptation

PURPOSE. To determine using the multifocal ERG technique whether there are any regional differences in the increase in the amplitude of cone electrore tinograms (ERGs) during light adaptation. METHODS. Multifocal ERGs were recorded with the Visual Evoked Response Imag ing System from five normal subjects. Thirty-seven hexagonal stimulus eleme nts and a recording time of 60 seconds were used. After 20 minutes of dark adaptation, multifocal ERGs were repeatedly recorded every 2 minutes over a period of 16 minutes. The amplitudes of the multifocal ERGs at different e ccentricities were compared during the 16 minutes of light adaptation. RESULTS. During the 16 minutes of light adaptation, the summed responses of the multifocal ERGs increased in amplitude an average of 36% and 47% for t hr negative and positive components, respectively. The magnitude of increas e was minimal in the central retina at 22% and was significantly larger in the peripheral retina at 58%. The implicit time was slightly increased (<4% ) with light adaptation, but there were no regional differences. CONCLUSIONS. The results demonstrated that there are topographic variations in the amplitude increase of cone ERGs during light adaptation. This topog raphic variation indicates that the mechanism for the increase must be base d on known regional differences in the retina.