EYE DISORDERS - Medicine for Mountaineering and Other Wilderness Activities - page 203

cornealulcers,andprovidecrispervisionforpeoplewithastigmatism.Theirdisadvantages
in outdoor settings include a profound foreign body sensation when dust or other particles
are in contact with the lens. People may also find the cumbersome requirement of daily
cleaning and maintenance unfeasible. In addition, hard contact lenses are not designed for
overnight use, tend to be dislodged easier, and may lead to a sensation of dryness and grit-
tiness at altitude.
Soft lenses come in a variety of types and designs. Some are designed for one-day dis-
posableuse;theycomeinsterileindividualpackages,andafteronedayarediscarded.Oth-
ers are designed to be used for months, requiring cleaning on a nightly basis. Others are
designedforextendedwear,allowingpeopletokeepthelensesinovernightformanydays;
these offer a variety of advantages, particularly requiring less maintenance and cleaning.
However, extendedwear lenses also are associated with at least a tenfold increased risk of
corneal ulcers.
In general, contact lenses often prove cumbersome and unfeasible for those engaging
in outdoor activities, especially at high altitudes. Glasses often are no better, as they too
become cumbersome in such environments. A better option for many outdoor enthusiasts
may be refractive surgery.
LASIK and PRK
Laser-assisted in-situ keratomileusis (LASIK) and photorefractive keratectomy (PRK)
aresurgicalproceduresthatuseanexcimerlaser,whichproducesacoldbeamofultraviolet
light, to reshape the cornea to correct refractive errors. This laser is able to remove corneal
tissue without creating heat ordamage to surrounding tissue, which allows forvery precise
modeling of the cornea to shape it for a very specific refractive goal. LASIK is currently
more widely used than PRK; it offers the benefits of more rapid healing and visual correc-
tion and less discomfort. One disadvantage that LASIK and PRK have relative to glasses
or contact lenses is that they can exacerbate dry eye syndromes. If individuals seeking re-
fractive correction have dry eyes, these procedures may not be the best option for them,
especially if they plan on outdoor activities in which they are exposed to conditions that
also may cause or exacerbate dry eyes.
Though more investigation is needed on LASIKand PRK-treated eyes at altitude, these
procedures appear to be excellent options. A recent study on Mount Everest of a small
numberofclimberswhohadundergoneLASIKfoundrelativelystablerefractioncompared
to those wearing contact lenses. All the climbers retained excellent vision at base camp
(17,600 ft; 5370 m). Five of six reported no visual changes up to 26,400 feet (8050 m).
Two climbers reported slight changes at 27,000 and 28,500 feet (8230 and 8700 m) that
improvedwithdescent.Threeofthesixexperiencednovisualchangesuptothecollapsing
dome the summit (29,035 ft; 8850 m). As most outdoor enthusiasts, even most climbers,