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Refractive changes caused by hypoxia after laser in situ keratomileusis surgery
M L Nelson1, S Brady, T H Mader
1Ophthalmology Service, Madigan Army Medical Center, Tacoma, Washington 98431-5000, USA.
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.