Diurnal daylight phase affects the temporal properties of both the b-wave and d-wave of the human electroretinogram.

Aspects of the anatomy and physiology of the cone pathway are known to vary according to the phase of the natural light cycle. Using a prolonged flash stimulus ( approximately 200 ms), we have examined the human electroretinogram (ERG) over a 24 h period. We report that whilst the a-wave of the photopic ERG does not alter, there are profound effects upon the implicit times of both the b-wave and d-wave components. Both components are significantly slower in the night-time period and systematically become faster (15-22% reduction in implicit time), reaching a peak at around midday. The daily variation in the temporal properties of the ERG is abolished by constant light, but is retained during constant darkness. The data suggest that the changes in the temporal properties of the cone pathway affect both cone-ON and cone-OFF pathways. This suggests that the diurnal effect is presynaptic to the second order neurones, and most likely resides in the cone synapse.