title: Intraocular pressure during a very high altitude climb.
abstract: OBJECTIVE
  Reports on intraocular pressure (IOP) changes at high altitudes have provided inconsistent and even conflicting
  
  
  RESULTS
  The purpose of this study was to investigate the effect of very high altitude and different ascent profiles on IOP in relation to simultaneously occurring ophthalmic and systemic changes in a prospective study.
  
  
  METHODS
  This prospective study involved 25 healthy mountaineers who were randomly assigned to two different ascent profiles during a medical research expedition to Mt. Muztagh Ata (7,546 m/24,751 ft). Group 1 was allotted a shorter acclimatization time before ascent than was group 2. Besides IOP, oxygen saturation (SaO(2)), acute mountain sickness symptoms (AMS-c score), and optic disc appearance were assessed. Examinations were performed at 490 m/1,607 ft, 4,497 m/14,750 ft, 5,533 m/18,148 ft, and 6,265 m/20,549 ft above sea level.
  
  
  RESULTS
  Intraocular pressure in both groups showed small but statistically significant changes: an increase during ascent from 490 m/1,607 ft to 5,533 m/18,148 ft and then a continuous decrease during further ascent to 6,265 m/20,549 ft and on descent to 4,497 m/14,750 ft and to 490 m. Differences between groups were not significant. Multiple regression analysis (IOP-dependent variable) revealed a significant partial correlation coefficient of beta = -0.25 (P = 0.01) for SaO(2) and beta = -0.23 (P = 0.02) for acclimatization time.
  
  
  CONCLUSIONS
  Hypobaric hypoxia at very high altitude leads to small but statistically significant changes in IOP that are modulated by systemic oxygen saturation. Climbs to very high altitudes seem to be safe with regard to intraocular pressure changes.
authors.affiliation: Department of Ophthalmology, University Hospital, Zurich, Switzerland.
authors.forename: Martina M
authors.initials: MM
authors.lastname: Bosch
authors.forename: Daniel
authors.initials: D
authors.lastname: Barthelmes
authors.forename: Tobias M
authors.initials: TM
authors.lastname: Merz
authors.forename: Frederic
authors.initials: F
authors.lastname: Truffer
authors.forename: Pascal B
authors.initials: PB
authors.lastname: Knecht
authors.forename: Benno
authors.initials: B
authors.lastname: Petrig
authors.forename: Konrad E
authors.initials: KE
authors.lastname: Bloch
authors.forename: Urs
authors.initials: U
authors.lastname: Hefti
authors.forename: Gregor
authors.initials: G
authors.lastname: Schubiger
authors.forename: Klara
authors.initials: K
authors.lastname: Landau
mesh_terms: D000064:Acclimatization / Q000502:physiology; D000328:Adult; D000531:Altitude; D000532:Altitude Sickness / Q000503:physiopathology*; D005260:Female; D006801:Humans; D000860:Hypoxia / Q000503:physiopathology*; D007429:Intraocular Pressure / Q000502:physiology*; D008297:Male; D008875:Middle Aged; D009051:Mountaineering; D009898:Optic Disk / Q000473:pathology; D010100:Oxygen / Q000378:metabolism; D010101:Oxygen Consumption / Q000502:physiology*; D011446:Prospective Studies; D014065:Tonometry, Ocular
chemical_list: D010100:Oxygen