Flicker electroretinogram in retinitis pigmentosa

Electroretinograms (ERGs) were recorded as a function of flicker frequency from 5 to 50Hz for 14 retinitis pigmentosa (RP) patients, 12 normal subjects and 1 rod monochromat. Data were analyzed by measuring the angular position of the response maximum, i.e. the phase, as a function of pulse-train frequency. Flicker ERGs obtained from the RP patients showed non-linear, frequency-dependent phase shifts when compared to the normal data. These phase shifts were simulated in a normal observer by attenuating the stimulus luminance by 1 log unit. However, the shape of the waveforms recorded from the normal differed markedly from those recorded from the RP patients. The differences, but not the ratios of the times-to-peak of the positive and negative ERG wavelets were longer in the RP patients than in the normal. These data suggest that the temporal anomalies in the RP flicker ERG are most likely due to changes in the amplitudes and time constants of the ERG components, and not simply to a reduced quantum catch or photoreceptor loss.