Time-of-day variations in oculomotor function: II. Steady-state accommodation to square-wave gratings.

Time-of-day variations in both tonic accommodation and steady-state accommodation to a grating were assessed for 16 observers who were tested once in the morning and again 12 hours later. The mean night-time tonic accommodation was +0.5 D greater than the morning value. Square-wave gratings of 4.2 and 8.4 c/deg were presented to the observers at distances of 0, 1.07, 2.13, 3.2 D. Over-accommodation to far targets and under-accommodation to near targets occurred for both gratings. All values of steady-state accommodation were somewhat greater in the evening. Large individual differences were noted.