title: Intraocular pressure and acclimatization to 4300 M altitude.
abstract: BACKGROUND
  Studies were conducted to determine the effect of altitude exposure on intraocular pressure (IOP) and any relationship with the severity of acute mountain sickness (AMS).
  
  
  OBJECTIVE
  a) IOP is decreased during exposure to 4300 m altitude; b) there is a positive correlation between IOP and AMS; and c) there is a correlation between changes in urinary catecholamines and IOP.
  
  
  METHODS
  IOP (noncontact tonometry) was measured in 11 resting males during acute simulated altitude (446 mmHg, < 2 h, hypobaric chamber), during altitude acclimatization (15 d at 4300 m), and in 6 of the 11 volunteers during re-exposure in the chamber after 8 d at sea level (Study A). In a second study (Study B) of 12 females, IOP (contact tonometry) and 24-h urinary catecholamines were measured during a 50-h chamber exposure (446 mmHg). AMS severity was assessed using the Environmental Symptoms Questionnaire (ESQ-C).
  
  
  RESULTS
  IOP decreased 25% after 2 d at altitude and returned toward sea level values by 15 d (Study A). IOP was reduced 13% after 5 h of exposure followed by return toward sea level values (Study B). Significant correlation was found between the sea level IOP and ESQ-C (Study A); significant correlation was found between the reduction in IOP and the ESQ-C and urinary epinephrine concentrations (Study B).
  
  
  CONCLUSIONS
  Altitude exposure resulted in a reduction in IOP that occurred within hours and recovered during acclimatization. This reduction may be related to increases in epinephrine concentration. Measurement of IOP before and during altitude exposure may provide an objective method of assessing an individual's response to hypoxic stress.
authors.affiliation: Thermal and Mountain Medicine Division, US Army Research Institute of Environmental Medicine, Natick, MA 01760-5007, USA. allen.cymerman@na.amedd.army.mil
authors.forename: A
authors.initials: A
authors.lastname: Cymerman
authors.forename: P B
authors.initials: PB
authors.lastname: Rock
authors.forename: S R
authors.initials: SR
authors.lastname: Muza
authors.forename: T P
authors.initials: TP
authors.lastname: Lyons
authors.forename: C S
authors.initials: CS
authors.lastname: Fulco
authors.forename: R S
authors.initials: RS
authors.lastname: Mazzeo
authors.forename: G
authors.initials: G
authors.lastname: Butterfield
authors.forename: L G
authors.initials: LG
authors.lastname: Moore
mesh_terms: D000064:Acclimatization; D000328:Adult; D000531:Altitude; D000532:Altitude Sickness / Q000503:physiopathology; D000704:Analysis of Variance; D001274:Atmospheric Pressure; D002395:Catecholamines / Q000652:urine; D005260:Female; D006801:Humans; D007429:Intraocular Pressure; D008297:Male; D014065:Tonometry, Ocular / Q000379:methods
chemical_list: D002395:Catecholamines