The etiology of refractive changes at high altitude after radial keratotomy. Hypoxia versus hypobaria.

Objective: Refractive changes at high altitude that occur after radial keratotomy (RK) may be caused by hypoxia or hypobaria.
Design: A prospective study was performed to evaluate the effects of hypoxia on RK and non-RK corneas.
Participants: There were 20 RK and 20 control eyes.
Intervention: These eyes were subjected to ocular surface hypoxia using an air-tight goggle system at sea level for 2 hours.
Main Outcome Measures: Keratometry, cycloplegic refraction, and pachymetry were evaluated using repeated measures analysis of variance.
Results: A significant hyperopic shift (P < 0.0001) and corneal flattening (P < 0.0013) occurred in all subjects with RK compared with those of control subjects. Corneal thickening occurred symmetrically in both groups.
Conclusions: These results suggest that refractive changes in subjects with RK occur at high altitude as a direct result of corneal hypoxia.