title: High incidence of optic disc swelling at very high altitudes.
abstract: OBJECTIVE
  To determine the incidence of optic disc swelling as a possible indicator of cerebral edema in a large group of healthy mountaineers exposed to very high altitudes and to correlate these findings with various clinical and environmental factors and occurrence of acute mountain sickness and high-altitude cerebral edema.
  
  
  METHODS
  This multidisciplinary, prospective, observational cohort study was performed in 2005 within the scope of a medical research expedition to Muztagh Ata (7546 m [24,751 ft]) in Western Xinjiang Province, China. Twenty-seven healthy mountaineers aged 26 to 62 years participated. Medical examinations were performed in Switzerland 1 month before and 4 1/2 months after the expedition. Ophthalmologic examinations were performed at 4 high camps (maximum elevation, 6865 m [22,517 ft]). Optic disc status was documented using digital photography. Further assessments included arterial oxygen saturation and cerebral acute mountain sickness scores.
  
  
  RESULTS
  Sixteen of 27 study subjects (59%) exhibited optic disc swelling during their stay at high altitudes, with complete regression on return to lowlands. Significant correlation was noted between optic disc swelling and lower arterial oxygen saturation (odds ratio, 0.86 per percentage of arterial oxygen saturation; 95% confidence interval, 0.81-0.92; P < .001), younger age (odds ratio, 0.95 per year; 95% confidence interval, 0.90-0.99; P = .03), and higher cerebral acute mountain sickness scores (odds ratio, 2.32 per 0.1 point; 95% confidence interval, 1.48-3.63; P < .001).
  
  
  CONCLUSIONS
  Optic disc swelling occurs frequently in high-altitude climbers and is correlated with peripheral oxygen saturation and symptoms of acute mountain sickness. It is most likely the result of hypoxia-induced brain volume increase.
authors.affiliation: Department of Ophthalmology, University Hospital Zurich, Frauenklinikstrasse 24, 8091 Zurich, Switzerland. martina.boesch@bluewin.ch
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: Konrad E
authors.initials: KE
authors.lastname: Bloch
authors.forename: Alexander J
authors.initials: AJ
authors.lastname: Turk
authors.forename: Urs
authors.initials: U
authors.lastname: Hefti
authors.forename: Florian K P
authors.initials: FK
authors.lastname: Sutter
authors.forename: Marco
authors.initials: M
authors.lastname: Maggiorini
authors.forename: Maria G
authors.initials: MG
authors.lastname: Wirth
authors.forename: Otto D
authors.initials: OD
authors.lastname: Schoch
authors.forename: Klara
authors.initials: K
authors.lastname: Landau
mesh_terms: D000328:Adult; D000532:Altitude Sickness / Q000150:complications* / Q000503:physiopathology; D001929:Brain Edema / Q000209:etiology / Q000503:physiopathology; D005260:Female; D006801:Humans; D015994:Incidence; D008297:Male; D008875:Middle Aged; D009051:Mountaineering; D009898:Optic Disk / Q000473:pathology*; D010101:Oxygen Consumption; D010211:Papilledema / Q000209:etiology* / Q000503:physiopathology; D011446:Prospective Studies