title: Hyperopic shift induced by high altitude after radial keratotomy.
abstract: BACKGROUND
  The collagen fibrils embedded in the ground substance of the stromal lamellae provide the structural support for the cornea. When the stromal lamellae are cut in a radial keratotomy surgical procedure, the remaining uncut lamellae carry the tensile forces.
  
  
  METHODS
  We studied two expert climbers who had bilateral radial keratotomy before participating in six climbs of extreme altitude, including Mount McKinley and above 7500 m (24,606 ft) on Mount Everest.
  
  
  RESULTS
  Whenever either climber was exposed to altitudes greater than approximately 5000 m (16,405 ft) for more than a day, their refraction would become +3.00 D or more hyperopic and remain so al long as they were at or above this altitude. Visual acuity slowly returned to normal after descent.
  
  
  CONCLUSIONS
  It appears that in the presence of significantly reduced atmospheric pressure and/or oxygen there is a greater effect of radial keratotomy in some patients, making the cornea more vulnerable to changes in shape. The cornea appears to respond by further flattening, exacerbating the intended surgical effect and producing a refractive shift toward hyperopia.
authors.affiliation: Moran Eye Center, University of Utah, Salt Lake City 84132, USA.
authors.forename: D J
authors.initials: DJ
authors.lastname: Creel
authors.forename: A S
authors.initials: AS
authors.lastname: Crandall
authors.forename: M
authors.initials: M
authors.lastname: Swartz
mesh_terms: D000328:Adult; D000531:Altitude; D003315:Cornea / Q000503:physiopathology / Q000601:surgery*; D006801:Humans; D006956:Hyperopia / Q000209:etiology* / Q000503:physiopathology; D007646:Keratotomy, Radial; D008297:Male; D009216:Myopia / Q000503:physiopathology / Q000601:surgery*; D014792:Visual Acuity