COURTESY OF ROBERT ROACH Researchers working in the Altitude Research Center. (Photo by Glenn Asakawa/University of Colorado)
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Last June, 28-year-old British climber Peter Kinloch achieved his lifelong goal of summiting Mount Everest. But on the descent, something went wrong. Kinloch began stumbling and slipping, went blind, and could not continue down the mountain. Medicating and oxygenating him proved unsuccessful, and with the weather worsening, the Sherpas guiding Kinloch had to leave him to die at 8,600 meters.
Mountaineers often report compromised vision at high altitudes where oxygen is scarce, and this problem can occur in concert with a suite of other symptoms that spell real trouble for someone traversing precarious trails thousands of meters up jagged peaks. But the link between hypoxic conditions, acute mountain sickness (AMS), and vision is poorly understood.
According to ophthalmologist Gabriel Willmann, if changes in the eye are linked to AMS—symptoms of which are nausea, headaches, fatigue, and dizziness—it may be possible to develop a diagnostic test that could save the lives of mountaineers like Kinloch. Willmann and other researchers have taken their research to the tops of massive mountains to investigate whether functional or structural changes in the eye might herald the onset of AMS. “The pathophysiology of AMS hasn’t been understood in a deep way,” says Willmann. “We can’t predict who gets sick and who doesn’t.”
Last summer, Willmann and his team set up an ophthalmology lab—complete with more than a ton of diagnostic equipment—at the Capanna Margherita, a mountaineers’ hostel and observatory at 4,554 meters on Monte Rosa, in the Pennine Alps, on the Swiss-Italian border. The Tübingen High Altitude Ophthalmology (THAO) study enlisted fourteen climbers, whose heart rate, qualitative AMS scores, and oxygen saturation were monitored regularly over the multi-day climb. The day after the climbers reached the summit, the researchers performed fluorescein angiography, a technique for examining circulation in the retina with a tracer dye—the first time this analysis had ever been done at high altitude.
Hypoxia is a strong stress on the body that produces many outcomes that researchers need to weed through.
According to Willmann, who reported preliminary results from the study at a conference on hypoxia earlier this year, the dye accumulated in the vessels peripheral to the retina in seven of the climbers, indicating leakage and damage; and in one climber the retinal vessels leaked blood due to damage from hypoxia. But only two of the climbers with leakage showed symptoms of AMS, suggesting there was no correlation between the leakage and altitude sickness. Willmann continues to study whether other changes in the eye—optic nerve sheath diameter, for example—correlate with AMS.
That remains an open question in the view of Robert Roach, a physiologist who directs the Altitude Research Center at the University of Colorado Denver. In a 2008 study on Everest, at altitudes much higher than in the THAO study, Roach did find a correlation between an increase in the diameter of the optic nerve sheath and AMS, but he cautions it hasn’t been repeated. “Hypoxia is a strong stress on the body that produces many outcomes that researchers need to weed through,” he says.
While a definitive link between vision and AMS remains elusive, Willmann’s interests in high altitude research lead beyond altitude sickness. In 2008, he and Tejvir Khurana, who studies Duchenne muscular dystrophy, a congenital disease that can cause respiratory insufficiency, climbed Mount Everest and performed color vision tests on themselves over the 54-day expedition to test whether color-sensing neurons in the eye are susceptible to hypoxia. They found that as they climbed higher, the eye’s threshold for discriminating blue from green increased. However, the sample size was small, and there is still no general consensus on whether color discrimination is affected by hypoxia. Khurana, a University of Pennsylvania physiologist, adds that if further research confirms the link between hypoxia and altered visual perception, changes in color vision or other eye abnormalities could help doctors diagnose hypoxia in Duchenne muscular dystrophy patients—as well as in extreme mountain climbers.