title: Corneal thickness at high altitude.
abstract: OBJECTIVE
  The eye, like other organs, is affected by the hypobaric hypoxia of high altitude. Corneal swelling is known to occur under hypoxic conditions at sea level, for instance when wearing contact lenses. The aim of this study was to measure central corneal thickness (CCT) in lowlanders ascending to altitude.
  
  
  METHODS
  The Apex 2 medical research expedition provided the opportunity to measure CCT in 63 healthy lowlanders. The subjects arrived in La Paz, Bolivia (3700 m), where they spent 4 days acclimatizing before being driven over 2 hours to the Cosmic Physics Laboratory at Chacaltaya (5200 m), where they stayed for 7 days. CCT was measured in the early afternoon by using ultrasound pachymetry on the first, third, and seventh day at 5200 m and before and after the expedition at sea level.
  
  
  RESULTS
  Mean CCT increased significantly from 543 microm at sea level to 561 microm on the first day at 5200 m (P < 0.001). This continued to increase to 563 microm on the third day and 571 microm on the seventh day but returned to 541 microm after descent to sea level.
  
  
  CONCLUSIONS
  This study showed that altitude caused a significant increase in CCT in a large group of healthy lowlanders with normal corneas. This finding confirms the results of previous studies and is likely to be caused by endothelial dysfunction causing stromal swelling. This could potentially cause visual problems for high-altitude mountaineers among whom refractive surgery is popular.
authors.affiliation: Sunderland Eye Infirmary, Sunderland, United Kingdom. danielsmorris@hotmail.com
authors.forename: Daniel S
authors.initials: DS
authors.lastname: Morris
authors.forename: John E A
authors.initials: JE
authors.lastname: Somner
authors.forename: Kirsten M
authors.initials: KM
authors.lastname: Scott
authors.forename: Ian J C
authors.initials: IJ
authors.lastname: McCormick
authors.forename: Peter
authors.initials: P
authors.lastname: Aspinall
authors.forename: Baljean
authors.initials: B
authors.lastname: Dhillon
mesh_terms: D000293:Adolescent; D000328:Adult; D000531:Altitude; D001274:Atmospheric Pressure; D003315:Cornea / Q000000981:diagnostic imaging / Q000473:pathology*; D015715:Corneal Edema / Q000000981:diagnostic imaging / Q000209:etiology*; D005260:Female; D006801:Humans; D000860:Hypoxia / Q000150:complications*; D008297:Male; D033401:Microscopy, Acoustic; D008875:Middle Aged