EYE DISORDERS - Medicine for Mountaineering and Other Wilderness Activities - page 196

The cornea is extremely important in vision; it protects the inside of the eye from the out-
side environment, and it provides two-thirds ofthe focusing power forlight that eventually
reaches the retina.
Dry Eye
Dry eye can become very troublesome for those engaged in outdoor activities. Dry eye
is a general term describing disorders of the film of tears that covers the surface of the eye.
These disorders include decreased production, increased evaporation, or an imbalance or
abnormality of the mucin or lipid layers of the tear film. Though a dry eye syndrome is as-
sociated with autoimmune disease, outdoors enthusiasts would rarely be dealing with that
disorder. In an outdoor setting, and for those who have no history of autoimmune disease,
dry eye is most likely caused by increased exposure to elements such as wind, dry air, or
ultraviolet light. Common symptoms of dry eye include a dry or gritty sensation, itching,
pain, photophobia, tearing, and redness. If the symptoms are mild, they can usually be ad-
equately treated for individuals to continue their activities. Insertion of artificial tears four
times a day and a lubricating ointment at bedtime usually relieve the symptoms.
Snow Blindness and Other UV Damage
The surface of the eye—the cornea and conjunctiva—absorbs ultraviolet radiation just
as the skin does. Excessive acute exposure can result in sunburn of the cornea and produce
snow blindness. During the period of exposure, no sensation other than the intensity of the
light serves to warn that sunburn is occurring. Symptoms may not develop until eight to
twelve hours later. When they do develop, they include a dry or gritty sensation, irritation,
photophobia, pain, redness, tearing, and swelling of the eyelids. A severe case of snow
blindness may be disabling for several days and may even lead to ulceration of the cornea,
permanently damaging the eye. Snow blindness should be prevented by consistently wear-
ing protective goggles or sunglasses. Any ultraviolet blocking lens is sufficient. Glasses
should be large and curved or have side covers to block reflected light coming from be-
low and from the sides. When ultraviolet radiation exposure is high, as it would be on a
concave high-altitude snowfield, goggles are safer, even though they may be less comfort-
able and tend to fog. Spare goggles or glasses should be carried, but emergency lenses can
be made of cardboard with a thin slit or pinhole to see through. The eyes may be covered
alternately so that only one eye at a time is exposed to sunlight. Eye protection is just as
necessary on a cloudy or overcast day as it is in full sunlight. Snow blindness can occur
during a snowstorm if the cloud cover is thin.
Snow blindness heals spontaneously in a few days. A significant concern though, is the
potential for infection. The damage to the cornea removes part or sometimes all of the epi-
thelial barrier in areas of the cornea, which is the protective barrier that prevents infection
when germs reach the surface of the eye. If this barrier is gone, infection is much more