Twenty-four-hour pattern of intraocular pressure in the aging population

PURPOSE. TO characterize the 24-hour pattern of intraocular pressure (IOP) in a sample of the aging human population. METHODS. Twenty-one healthy volunteers 50 to 69 rears of age were housed in a sleep laboratory fur 24 hours. Experimental conditions were strictly con trolled with a 16-hour light period :md an 8-hour dark period. Sleep was en couraged in the dark period. Intraocular pressure was measured using a pneu matonometer every 2 hours (total of 12 times). Measurements were taken in b oth the sitting position and the supine position during the light/wake peri od but only in the supine position during the dark period. RESULTS. When the sitting IOP data from the light/wake period and the supin e IOP data from the dark period were considered, elevation and reduction of IOP occurred around the scheduled lights-off and lights-on transitions, re spectively. Mean IOP in the dark period was significantly higher than mean IOP in the light/wake period. The trough appeared at the end of the light/w ake period, and the peak appeared at the beginning of the dark period. The magnitude of trough-peak difference was 8.6 +/- 0.8 mm Hg (mean +/- SEM). C osine fits of 24-hour IOP data showed a significant 24-hour rhythm. When IO P data from just the supine position were analyzed, the trough-peak IOP dif ference was 3.4 +/- 0.7 mm Hg, with similar clock times for the trough and the peak. Cosine fits of supine IOP data showed no statistically significan t 24-hour rhythm. CONCLUSIONS. Nocturnal elevation of IOP occurred in this sample of the agin g population. The trough of IOP appeared at the end of the light/wake perio d, and the peak appeared at the beginning of the dark period. The main fact or in the nocturnal IOP elevation appeared to be the shift from daytime upr ight posture to supine posture at night.