Stability of laser-assisted in situ keratomileusis (LASIK) at altitude.
BACKGROUND
The U.S. Air Force approved laser-assisted in situ keratomileusis (LASIK) for aircrew in May 2007. Relative to photorefractive keratectomy (PRK), LASIK potentially offers a more rapid return to flight status; however, there are concerns regarding corneal stability at altitude after surgery. Studies have shown that hypoxia induces a myopic shift in LASIK eyes. Mountaineers treated with LASIK have similarly reported decreased distance acuity when climbing above 22,000 ft (6706 m). We evaluated visual and refractive stability after LASIK under conditions simulating an operational aviation mission.


METHODS
There were 24 eyes of 12 active duty subjects that were examined 1 or more months after LASIK. Measurements of high and low contrast visual acuity, keratometry, and refractive error were performed at ground level after a 2-h oxygen pre-breathe and repeated after 30 min of exposure to conditions simulating 35,000 ft (10,668 m) using a hypobaric chamber. A within subject, repeated measures t-test was used to compare findings at altitude to ground level.


RESULTS
LASIK eyes demonstrated no clinically or statistically significant changes at altitude relative to ground level for the four parameters studied. No eyes showed more than +/-0.25 D of change on keratometry and none had a myopic shift greater than 0.25 D.


CONCLUSIONS
LASIK eyes exposed to extreme altitudes under operational conditions, where the exposure is limited to 30 min or less, are expected to remain stable.
U.S. Air Force School of Aerospace Medicine, Ophthalmology Branch, 2510 5th St., Wright-Patterson AFB, OH 45433-7913, USA.
Michelle
M
Aaron
Steve
S
Wright
John
J
Gooch
Rich
R
Harvey
Ryan
R
Davis
Charles
C
Reilly
D000328:Adult; D000531:Altitude; D003315:Cornea / Q000503:physiopathology*; D005260:Female; D006801:Humans; D020731:Keratomileusis, Laser In Situ / Q000009:adverse effects; D008297:Male; D008875:Middle Aged; D009216:Myopia / Q000209:etiology / Q000503:physiopathology; D012030:Refractive Errors / Q000209:etiology / Q000503:physiopathology; D014792:Visual Acuity; D055815:Young Adult