Elevation of human intraocular pressure at night under moderate illumination

PURPOSE. An endogenous elevation of intraocular pressure (IOP) occurs at ni ght in healthy young adults. The authors studied whether or not this IOP el evation can be detected under moderate illumination. METHODS. Twenty-five healthy volunteers, ages 18 to 25 years, were housed o vernight in a sleep laboratory under a strictly controlled light-dark envir onment. Intraocular pressure was measured in the supine position every 2 ho urs, using a pneumatonometer. An 8-hour sleep period was assigned to each v olunteer according to individual's accustomed sleep cycle, in the early par t of this assigned period, sleep was encouraged with room lights off. Resea rchers performed IOP measurements at two time points with the aid of night vision goggles. In the middle to the late part of the assigned period, ligh ts were turned on twice for a 1-hour interval. The light intensity was the same as before the bedtime. At the ending of each light period, IOP was mea sured under illumination. RESULTS. Average IOP was significantly higher in the assigned sleep period versus outside the period. The trough of mean IOP occurred just before the bedtime, and then IOP gradually increased and peaked at the end of the 8-ho ur assigned sleep period. The difference between the trough and peak IOP wa s 3.5 +/- 0.7 mm Hg (mean +/- SEM, n = 25). Within the assigned sleep perio d, the average IOP determined under illumination was significantly higher t han the average IOP preceding the illumination. CONCLUSIONS. Elevation of IOP occurred during the assigned sleep period wit h two 1-hour light exposures of moderate intensity. Environmental light at night had no significant effect on the nocturnal IOP elevation in healthy y oung adults.