Abstract

Systematic variations in full-field ERG threshold have been reported in eyes of normal human subjects entrained to a 14 hour light: 10 hour dark daily cycle. Rod ERG thresholds were 0.13 log unit higher following light-onset than at other times of day (1). This threshold elevation is believed to reflect rod outer segment (ROS) shedding since the time course is similar to that documented in anatomical studies of shedding (2-4) and since neither rod responses of fellow eyes (1) nor rod responses in unentrained subjects (5) vary with time of day. The entrainment process takes 3 days, that is, by the third day of entrainment, the magnitude of the diurnal variation in rod ERG threshold is similar to that obtained following 7 or more days of entrainment (5). Light-onset is necessary to synchronize the rhythm since no increase in threshold is detectable at 9:30 am without light exposure at 8:00 am (5).

© 1987 Optical Society of America