NEW YORK, Mar 07 (Reuters Health) - Mountain climbers who have had their vision corrected through laser surgery may want to take their glasses along on the ascent anyway. New research shows the thin air of high altitudes may blur surgically corrected vision.

When researchers lowered the oxygen supply to the eyes of 40 study participants, they found that the 20 who had undergone LASIK surgery "shifted" toward near-sightedness. LASIK, or laser in situ keratomileusis, corrects poor vision by removing a thin layer of tissue from the cornea. But, according to a report in the March issue of Ophthalmology, the procedure may weaken the central cornea enough to blur patients' distance vision in low-oxygen environments.

This should be of greatest concern to mountain climbers, skiers, pilots and others who spend long periods of time at high altitudes, according to researchers led by Dr. Mark L. Nelson of the Madigan Army Medical Center in Tacoma, Washington.

LASIK surgery is a recently approved technique for correcting poor vision. The procedure is particularly popular among young people who want to be free from glasses during activities such as hiking, climbing and skiing, according to Nelson's team. What might happen in thin-air conditions after the surgery is unknown. The authors note there is evidence that low-oxygen conditions blur vision in patients who have undergone a related procedure called radial keratotomy.

In their study, Nelson and colleagues simulated thin-air conditions with a goggle system that cuts oxygen to one eye, while feeding normal oxygen levels to the other eye. While all the study participants showed certain changes in their oxygen-deprived corneas, the LASIK patients showed a significant "shift" to near-sightedness.

However, these findings do not mean high-climbing adventurers cannot undergo LASIK, according to the researchers. In a statement, co-author Dr. Lawrence J. White said, "I expect people could climb Everest after LASIK, but they might carry some glasses to help with any significant near-sightedness encountered."

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