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
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