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John H. K. Liu, Daniel F. Kripke, Rivak E. Hoffman, Michael D. Twa, Richard T. Loving, Katharine M. Rex, Brian L. Lee, Steven L. Mansberger, Robert N. Weinreb; Elevation of Human Intraocular Pressure at Night under Moderate Illumination. Invest. Ophthalmol. Vis. Sci. 1999;40(10):2439-2442.
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purpose. An endogenous elevation of intraocular pressure (IOP) occurs at night in
healthy young adults. The authors studied whether or not this IOP
elevation can be detected under moderate illumination.
methods. Twenty-five healthy volunteers, ages 18 to 25 years, were housed
overnight in a sleep laboratory under a strictly controlled light–dark
environment. Intraocular pressure was measured in the supine position
every 2 hours, using a pneumatonometer. An 8-hour sleep period was
assigned to each volunteer according to individual’s accustomed sleep
cycle. In the early part of this assigned period, sleep was encouraged
with room lights off. Researchers 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, lights 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 measured under
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-hour assigned sleep period. The difference between the trough and
peak IOP was 3.5 ± 0.7 mm Hg (mean ± SEM, n =
25). Within the assigned sleep period, the average IOP determined under
illumination was significantly higher than the average IOP preceding
conclusions. Elevation of IOP occurred during the assigned sleep period with
two 1-hour light exposures of moderate intensity. Environmental light
at night had no significant effect on the nocturnal IOP elevation in
healthy young adults.
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