BLOG: Is LASIK safe at altitude?
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The last place anyone wants to have an ophthalmic emergency is standing on top of Mount Kilimanjaro in Tanzania, at 19,341 feet above sea level and days from any medical care.
But my myopic patient was a mountaineer and had plans to summit Kilimanjaro, as well as dozens of other peaks in Africa and in South America. Before committing to refractive surgery, she wanted to know the risk at high altitudes to eyes that have had LASIK.
If your patient gets LASIK to facilitate high-altitude mountain climbing, will they be vulnerable to corneal failure? The mountaineering community has been sensitive to this question ever since the tragic experience of Texas pathologist Beck Weathers on Mount Everest in 1996. Weathers had undergone radial keratotomy, and when the extremely low oxygen levels above 20,000 feet caused corneal flattening and loss of functional vision, he struggled to find his base camp during an extreme storm. Weathers survived but with severe frostbite injuries to his hands and face.
Logistical obstacles limit our ability to do large studies of post-LASIK climbers at extreme altitudes, and published literature on the topic comprises only a few dozen cases. High altitude is a challenging environment for all corneas, and this challenge may be greater for any cornea that has undergone surgery.
The challenge is not due to lower atmospheric pressure, or hypobaria, but to decreased oxygen levels, or hypoxia. All working cells require oxygen to break glucose down into adenosine triphosphate, the essential fuel molecule of the body. Alone among all tissues of the body, the cornea gets its oxygen not from the blood, but from the atmosphere — it breaths it in, through the tear film, from the air. If it cannot get enough, as with a low-Dk contact lens or in a high-altitude environment, metabolism slows.
The amount of oxygen in a cubic meter of air at 20,000 feet is less than half of that at sea level; at the top of Everest, it drops to 33%. When atmospheric oxygen is poorly available, the resulting buildup of lactate and bicarbonate ions reduces the pumping ability of the endothelial cells, and the stroma overhydrates and thickens. In a cornea with a weakened apex, as in one that has undergone a central ablation, the center may steepen more than the periphery, causing myopic blur.
In 2001, two surgeons who had myopic LASIK with 20/20 or better uncorrected distance vision (UDVA) in all four eyes climbed Aconcagua in Argentina, to 22,841 feet, and took vision and peripheral oxygenation measurements at every 1,000-foot climb in elevation. All four eyes slowly suffered myopic blur, closely correlated with oxygen saturation. By the summit, three eyes had decreased to 20/100 UDVA or worse, and one had decreased to 20/30. All eyes recovered to 20/20 UDVA within 1 month of the ascent (Boes DA, et al). The climbers noted that the more recently operated eyes suffered from a greater and more long-lasting shift.
In 2003, six climbers ascended Mount Everest above 26,000 feet after myopic LASIK; one was forced to abandon the attempt due to poor vision, one turned around for other reasons, and four summited with good visual acuity.
The United States military has taken a keen interest in the topic, as LASIK has been an option for their aviators since 2007, but its studies have focused only on brief exposures to altitude, simulating a jet flight. Those studies have shown no issues in post-LASIK eyes up to 35,000 feet for up to 30 minutes (Aaron M, et al).
In short, we are far from a solid understanding of this topic. For most climbers, and certainly those who will not climb to extreme altitudes, the benefits of LASIK likely far exceed the risks. However, it seems prudent to counsel a 6-month waiting period after LASIK before any high-altitude exposure, and more careful climbers may consider packing eyeglasses of a low minus power just in case. Your patient would likely prefer not to climb to a once-in-a-lifetime view, only to be unable to see past their ice axe.
References:
- Aaron M, et al. Aviat Space Environ Med. 2012;doi:10.3357/asem.3325.2012.
- Boes DA, et al. J Cataract Refract Surg. 2001;doi:10.1016/s0886-3350(01)01074-4.
- Dimmig JW, et al. J Refract Surg. 2003;doi:10.3928/1081-597X-20030101-10.
- Krakauer J. Outside Magazine. 1996;46-66.
For more information:
Oliver Kuhn-Wilken, OD, practices at Pacific Cataract and Laser Institute’s Tualatin Clinic in Oregon.
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