While swelling commonly occurs in the corneas of mountain climbers at high altitudes, a new study shows it doesn't appear to affect visibility.
Lead researcher Dr Martina Monika Bosch, of University Hospital Zurich studied the effects of high-altitude climbing on corneal thickness among 28 healthy volunteers climbing Mount Muztagh Ata in western China.
The mountaineers were randomly assigned to two different ascending paths, with one group being allotted a shorter time to acclimate before ascending to 6,265 meters.
The researchers found that in groups with both patterns of ascent, corneal thickness increased with increasing altitude and decreased after descent, and the amount of decrease in blood oxygen levels paralleled this increase.
The group with the shorter acclimatization time experienced a greater increase in corneal thickness.
However, no significant decrease in visual acuity was observed in either group.
Although the exact cause of corneal swelling during ascent remains controversial, the current findings suggest that the body's delivery of oxygen to the aqueous humor-the fluid inside the eyeball, between the cornea and iris-may be more important in corneal oxygen levels than previously thought.
"It seems that visual acuity in healthy corneas is not adversely affected despite the presence of edema at altitudes up to 6,300 meters," said authors.
However, it is likely that ascents to more extreme altitudes-above 8,000 meters or about 26,000 feet-may induce greater damage to the cornea and lead to dangerous visual loss.
The findings appear in Archives of Ophthalmology, one of the JAMA/Archives journals.