Refractive changes caused by hypoxia after laser in situ keratomileusis surgery.

Objective: To determine whether hypoxia induces refractive changes in subjects who have had laser in situ keratomileusis (LASIK) refractive surgery.
Design: Prospective paired eye clinical trial.
Participants: There were 20 LASIK subjects (40 eyes) and 20 myopic non-LASIK controls (40 eyes).
Intervention: Each subject had one eye exposed to ocular surface hypoxia (humidified nitrogen) by use of an airtight goggle system at sea level for 2 hours. The other eye was simultaneously exposed to humidified, compressed air (21% oxygen) with the same airtight goggle system.
Main Outcome Measures: Keratometry, cycloplegic refraction, and pachymetry were compared before and after exposure by use of repeated measures analysis of variance.
Results: A significant myopic shift (P: < 0.01) occurred in LASIK corneas exposed to hypoxia compared with myopic control subjects. A significant increase in corneal thickening occurred symmetrically in both LASIK and control subjects exposed to hypoxia. There was a trend toward corneal steepening (keratometry) in LASIK subjects, but this was not statistically significant.
Conclusions: These results suggest that ocular surface hypoxia induces a myopic shift in LASIK subjects.