ExplorersWeb [everest] [K2] [oceans] [poles] [tech] [weather] [statistics] [medical]
BaseCampMD.com


Eye concerns at altitude

The following is edited from “The Eye in the Wilderness” in Wilderness Medicine (Auerbach, ed Mosby publ) submitted to BaseCampMD by Capt Frank Butler, Jr. MD

High-Altitude Retinal Hemorrhage
There are many reports of retinal hemorrhages in mountain climbers. These have been described as high-altitude retinal hemorrhages (HARH) or as part of the more inclusive term altitude retinopathy. Some researchers have reported an incidence of HARH of 29% in climbers on a Mt. Everest expedition at altitudes ranging from 5300 to 8200 m (17,385 to 26,896 feet,) and others found that 56% of their subjects had HARH at an altitude of 5360 m (17,581 feet.) HARH has been discovered in 4% of 140 trekkers examined at 4243 m (13,917 feet) at Pheriche in the Himalayas. Scientists have also found a significant correlation of retinal hemorrhages with symptoms of acute mountain sickness (AMS). Differences in incidence of HARH for exposures at similar altitudes may be due to differences in time at altitude before examination, acclimatization schedule, exercise levels, examination techniques, and the presence of concurrent conditions that may predispose to HARH.

Although HARHs are often not associated with acute visual symptoms, they may result in a loss of visual acuity or paracentral scotomas. There is a reported case in which further ascent after the development of HARH resulted in additional lesions. HARH that results in decreased visual acuity should be a contraindication to further ascent. Some experts recommend that evacuation of individuals with decreases in visual function resulting from HARH (in the absence of high-altitude cerebral edema [HACE] or high-altitude pulmonary edema [HAPE] ) be considered nonemergent unless reexamination indicates a progressive deterioration of vision or increasingly severe retinopathy. HARH resolves over a period of 2 to 8 weeks after the altitude exposure is terminated. Recognizing advancing grades of HARH may allow physicians to recommend initiating treatment with oxygen, steroids, diuretics, and immediate descent to prevent HAR progression, macular involvement, or potentially fatal HACE. High altitude retinopathy is both a significant component of and a predictor of progressive altitude illness.

Contact Lenses in Mountaineering
Contact lenses may be used successfully at high altitude, but use at altitude during trekking or mountaineering entails several considerations beyond those encountered in normal use. In general, overnight use of extended-wear contact lenses is not recommended because of the associated increased rate of microbial keratitis. Even soft contact lenses decrease the oxygen available to the cornea. Lid closure during sleep further accentuates corneal hypoxia. Removing contact lenses at night, however, 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. Lastly, wearing contact lenses can make eyes more sensitive to glare.

Guidelines for military personnel using contact lenses in austere environments have been developed and apply to the expedition setting:
1. Disposable extended-wear lenses may be left in the eye for up to 1 week. If the wearer is still in the field at the end of this period, the lenses should be removed and discarded. After an overnight period without lenses, new lenses may be inserted, with strict attention to contact lens hygiene.
2. Contact lens wearers should always have backup glasses available for use in the wilderness in case a lens is lost or becomes painful.
3. 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.
4. Contact lens wearers often note that their eyes become dry. This discomfort may be alleviated with contact lens rewetting drops.
5. Contact lens wearers often note increased sensitivity to sunlight. Individuals who wear contact lenses in the field during daylight hours should carry sunglasses.

Continuous wearing of disposable contact lenses for a week, followed by discarding of the lenses and insertion of fresh lenses after an overnight period without a lens, is a controversial approach to contact lens wear in an expedition setting. Whether or not the reduction in lens handling offsets the increased risk of microbial keratitis resulting from overnight wear is not known. The decision to wear contact lenses while mountaineering should be made carefully in consultation with a personal ophthalmologist or optometrist. Microbial keratitis (corneal ulcers) can pose a significant threat to vision under the best of circumstances. Should this disorder occur with a 7- to 10-day delay to definitive ophthalmologic care, the danger of permanent loss of vision is great. Any eye pain that occurs in contacts lens wearers in the wilderness should be attended to urgently. Contact lenses that block out harmful UV rays are now available (Accuvue, Precision UV), but sunglasses are still a good idea both to help protect the eyes from drying wind effects and the eyelids from UV exposure even if contacts are worn. Considering all the potential problems, a good pair of prescription glacier glasses or laser refractive surgery might be a more reasonable alternative than contact lenses as a long-term solution to the refractive needs of mountaineers.

Refractive Changes at Altitude after Refractive Surgery
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. Another report describes two expert climbers who experienced hyperopic shifts of three diopters or more during altitude exposures of 5000 m (16,400 feet) or higher on Mt. McKinley and Mt. Everest. One report noted no refractive change after 6 hours in post-RK eyes at a simulated altitude of 3659 m, suggesting that the hyperopic shift requires more than 6 hours to develop. Further studies 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.
 

 

Snow blindness

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.

A sunny day on fresh snow can be beautiful, but incapacitating if you’re not protected. Keep in mind that the brightness can exceed 10-15 times the amount of light that is safe and comfortable for your eyes to accommodate.

Sometimes, when climbing on oxygen, the warm and moist breathing air will escape your oxygen mask upwards and sometimes clog up your goggles, especially upon climbing down. Your choice will then be to climb "blindfolded" or remove the glasses. You might choose to pull your glasses a bit out from your face, allowing the warm air to pass them. The suns rays will now be able to burn your eyes at the unprotected sides. An anti-fog lens cleaner may help in this situation.

If the weather is overcast you might be tempted to remove the glasses altogether. Yet the rays are just as harmful when cloudy, and the following morning you’ll be sorry. After 8 years of climbing it finally happened to us. It took only a short time without goggles at our summit descent (shooting film), we noticed nothing, and in the morning we were a mess.

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

bcmd logo