Are circadian variations in the electroretinogram evident on routine testing?

We sought to determine whether routine ERGs using ISCEV standard stimuli, would show a pattern of circadian variation. We examined ERGs from 40 successive normal subjects who were tested at different times during regular laboratory operating hours of 9 am to 4 pm, and also reviewed high intensity a-waves from a subgroup. There were no obvious associations of either ERG amplitude or implicit time with time of day. No statistically significant difference was found between average ISCEV ERG parameters or high-intensity a-wave parameters obtained in the morning (9 am to 1 pm) and afternoon (1 pm to 4 pm). We conclude that time of day is not critical for routine ERG recordings, although small, variable, circadian changes may well be present. We suggest that the time of day be noted on clinical recordings, in case this information becomes relevant for a particular patient.