High altitude mountaineering and extended backcountry trekking present several ophthalmic challenges to outdoor enthusiasts, among which are problems with contact lenses, problems with previous corneal surgery, and UV induced keratitis.
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Removing contact lenses at night … presents logistical problems in the mountaineering setting. Practicing acceptable lens hygiene during an expedition is difficult. The mountaineer who leaves contact lenses in a case filled with liquid solution in the tent outside of his or her sleeping bag at night may awaken to find the solution and lenses frozen solid.
All contact lens wearers should have backup spectacles, and this exhortation applies especially to those who spend extended amounts of time in the wilderness:
Contact lens wearers should always have backup glasses available for use in the wilderness in case a lens is lost or becomes painful.
In the event of bacterial keratitis related to contact lens wear, specialists recommend carrying topical antibiotics during all extended backcountry excursions:
Individuals who wear contact lenses on expeditions should carry both fluoroquinolone eye drops and contact lens rewetting solution. Both types of drops may freeze if not protected from the cold.
Individuals who have had laser refractive surgery should be especially careful when exploring at high altitudes:
An acute hyperopic shift in persons who have had radial keratotomy (RK) and then experience an altitude exposure has been reported in past years, and has been observed at altitudes as low as 2744 m (9000 feet). A dramatic example of this phenomenon was that experienced by Dr. Beck Weathers in the Everest tragedy of May 1996 in which eight climbers also lost their lives. Dr. Weathers had undergone bilateral RK years before the expedition. He noted a decrease in vision, which started early during his ascent. Author Jon Krakauer recalls that “. . . as he was ascending from Camp Three to Camp Four, Beck later confessed to me, ‘my vision had gotten so bad that I couldn’t see more than a few feet.“ This decrease in vision forced Dr. Weathers to abandon his quest for the summit shortly after leaving Camp Four and nearly resulted in his death.
The refractive shift mentioned above is most likely due to low oxygen levels specifically, not necessarily low atmospheric pressures found atop high mountains. Furthermore, PRK and LASIK appear to be far safer procedures for individuals in the habit of frequenting very high altitudes; even so, standard precautions still apply to those who have had laser corrective surgery and whose activities take them to extreme heights:
[S]tudies at 4299 m (14,100 feet) on Pike’s Peak revealed that: (1) subjects who had undergone RK demonstrated a progressive hyperopic shift associated with flattened keratometry findings during a 72-hour exposure; (2) control eyes and eyes that had undergone laser refractive surgery (photorefractive keratectomy [PRK]) experienced no change in their refractive state; (3) peripheral corneal thickening was seen on pachymetry in all three groups; and (4) refraction, keratometry, and pachymetry all returned to baseline after return to sea level. There is strong evidence that the effect of altitude exposures on post-RK eyes is caused by hypoxia rather than by hypobarism and that breathing a normoxic inspired gas mix will not protect against the development of hypoxic corneal changes.
There is compelling evidence for myopic mountaineers that PRK instead of RK is their refractive surgical procedure of choice. Individuals who have undergone RK and plan to undertake an altitude exposure of 2744 m (9000 feet) or higher while mountaineering should bring multiple spectacles with increasing plus lens power.
The most commonly performed laser refractive surgery at present is laser in-situ keratomileusis (LASIK). Several studies observed climbers having undergone LASIK and the authors’ conclusion was that LASIK may be a good choice for individuals involved in high altitude activities, but those achieving extreme altitudes of 7927 m (26,000 ft) and above should be aware of possible fluctuation of vision. Data suggest that a small refractive shift in the myopic direction may be present at extreme altitudes. Climbers who do not ascend beyond moderate altitudes should not experience a post-LASIK refractive shift.
Finally, wilderness and mountain enthusiasts should be especially careful to protect their corneas from UV-induced corneal damage. Below are guidelines for choosing eye protection for the outdoors:
Snow blindness, or solar/ultraviolet keratitis is an excruciatingly painful state that comes from the sun burning the covering of your eye — the cornea. And it happens, very commonly if you don’t wear sunglasses, or if you don’t wear appropriate sunglasses in any bright light situation – especially easy to encounter at altitude.
Here are some guidelines to use when choosing a good trekking/mountaineering pair of sunglasses:
– 99-100% UV absorption
– Polycarbonate or CR-39 lens (lighter, more comfortable than glass)
– 5-10% visible light transmittance
– Large lenses that fit close to the face
– Wraparound or side shielded to prevent incidental light exposure