Nocturnal elevation of intraocular pressure in young adults

PURPOSE. TO distinguish 24-hour (circadian) and postural effects on intraoc ular pressure (IOP) in healthy young adults. METHODS. Thirty-three volunteers were housed in a sleep laboratory for 1 da y under a strictly controlled 16-hour light and 8-hour dark environment. Sl eep was encouraged in the dark period. Intraocular pressure was measured in each eye every 2 hours using a pneumatonometer. Researchers used night-vis ion goggles to perform IOP measurements in the dark, while the subject's li ght exposure was minimized. In the first group of 12 subjects, measurements were taken with subjects in the sitting position during the light-wake per iod and supine during the dark period. In the second group of 21 subjects, all IOP measurements were taken with the subjects supine. RESULTS. Average IOP was significantly higher in the dark period than in th e light-wake period in both groups. The lowest IOP occurred in the last lig ht-wake measurement, and the peak IOP occurred in the last dark measurement . The trough-peak difference in IOP was 8.2 +/- 1.4 mm Hg (mean +/- SEM) in the first group. Intraocular pressure changed sharply at the transitions b etween light and dark. In the second group, the trough-peak IOP difference was 3.8 +/- 0.3 mm Hg. Intraocular pressure changed gradually throughout th e 24-hour period. In comparison with the sitting IOP in the first group, th e supine IOP in the second group was significantly higher during the light- wake period. CONCLUSIONS. Circadian rhythms of IOP were shown in young adults, with the peaks occurring in the late dark period. A nocturnal IOP elevation can appe ar independent of body position change, but change of posture from upright to recumbent may contribute to the relative nocturnal IOP elevation.