Diurnal variations in tonic accommodation.

Abstract

It has been established that many aspects of visual function undergo diurnal changes, but accommodation is an apparent exception. The authors studied tonic accommodation in three subjects to challenge this assumption. The measurements were done in complete darkness with a modified Hartinger refractometer whose light source was replaced by a red photodiode. This allowed exposure of the refractometer mark for a short duration and thus eliminated the accommodation stimulus. The measurement were taken every 4 hours five times a day starting from 8 AM. Before each measurement the subjects were kept in darkness for 10 minutes. To obtain a measure of tonic accommodation the authors used the method of limits. The results showed that tonic accommodation varied over the studied period of the day in a predictable manner characteristics for each individual--one subject had his peaks and troughs displaced compared with the other two subjects. The amplitude of the daily variation was on the order of approximately 1.0 D, but the day-to-day values were relatively stable within +/- 0.5 D. Results were compared with other published data and showed that tonic accommodation may be subject to diurnal variation.