title: Elevation of human intraocular pressure at night under moderate illumination.
abstract: OBJECTIVE
  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 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-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 the illumination.
  
  
  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.
authors.affiliation: Department of Ophthalmology, University of California, San Diego, La Jolla 92093-0946, USA. joliu@ucsd.edu
authors.forename: J H
authors.initials: JH
authors.lastname: Liu
authors.forename: D F
authors.initials: DF
authors.lastname: Kripke
authors.forename: R E
authors.initials: RE
authors.lastname: Hoffman
authors.forename: M D
authors.initials: MD
authors.lastname: Twa
authors.forename: R T
authors.initials: RT
authors.lastname: Loving
authors.forename: K M
authors.initials: KM
authors.lastname: Rex
authors.forename: B L
authors.initials: BL
authors.lastname: Lee
authors.forename: S L
authors.initials: SL
authors.lastname: Mansberger
authors.forename: R N
authors.initials: RN
authors.lastname: Weinreb
mesh_terms: D000293:Adolescent; D000328:Adult; D002940:Circadian Rhythm / Q000502:physiology*; D005260:Female; D006801:Humans; D007429:Intraocular Pressure / Q000502:physiology*; D008027:Light; D008297:Male; D014065:Tonometry, Ocular