Saturday, January 19, 2008

7.10 Because it's there

Sir Edmund Hillary (1919-2008) and Mr Tenzing Norgay (तेन्जिङ नोर्गे शेर्पा, 1914-1986) climbed Mount Qomolangma, as Mt Everest is called in Tibetan, and reached its summit together on May 29, 1953. Many have tried, while some have since succeeded, more have succumbed to various high-altitude (HA) illnesses, from exposure to both the extreme cold (i.e., frostbites) and the low atmospheric pressure (i.e., low O2 level). The oxygen level near the top of Mt Everest is actually 66% less than that at sea level. Depending on the altitudes and how fast the climbers ascend, these illnesses can be mild, e.g., acute mountain sickness (from accumulation of some fluid in the brain) and HA edema (swelling of hands, feet, and face). The more severe forms, HA pulmonary edema and HA cerebral edema can both be fatal. These illnesses are largely a result of hypoxia-induced leakage of plasma from the capillaries.

Interestingly, there are now findings that pertain to the eye, e.g., those reported in“The Eye in the Wilderness” in Wilderness Medicine (Auerbach PS, editor, Mosby publisher, 2001). Even though none of the eye problems can kill you, each can still be a nuisance when you are 29,000 feet above the sea with no medical facilities in sight - unless a fellow climber happens to be an eye doctor.

1. Retinal hemorrhage may develop at altitudes of >8,000 feet. There are no symptoms except if it occurs within the macula, then a small scotoma may result. This maybe similar to retinal hemorrhage from polycythemia vera (see image below), i.e., too many red cells that thicken the blood, impede blood circulation, and occlude retinal veins. Indeed, humans adapt to long-term high-altitude hypoxia by producing more red cells that often cause chronic mountain sickness.

(An example of retina hemorrhage - from central retinal vein occlusion)

2. Snow blindness or UV-keratitis. UV radiation increases at ca 5% every 1,000 feet above sea level and UV rays are reflected by the surface of snow/ice that further increases the intensity. If unprotected, the cornea and iris are injured. The eyes become red, painful, and photophobic. The North American Inuits have long used slit sunshields made from wood or bones to protect their eyes.

3. Contacts maybe a problem as well. The lack of atmospheric oxygen further aggravated the inherent corneal hypoxia with the contact lens wear. The climber should carry a pair of back-up glacier glasses. High-O2 transmitting silicone hygrogel lenses that have been approved for extended-wear should be used. And 4th generation fluoroquinolone eyedrops qdx7 days also should be used at the first sign of bacterial keratitis.

4. Climbers with radial keratotomy (RK) have reported drastic changes in vision in the form of a hyperopic shift. PRK and LASIK appear less affected. In all cases, there is a thickening of the peripheral cornea possibly from edema. And in the case of RK, the incision-weakened peri-central cornea probably becomes further flattened from changes in the periphery.

High-altitude illnesses can be reversed by moving down to lower altitudes. Some mountaineers believe that by drinking enough water, these illnesses can be avoided, presumably the blood can thus be "thinned". Perhaps researchers in HA medicine should examine this claim and provide some definitive answers.

For us couch potatoes, the question is always: "Why do you want to climb Mt Everest?" And George Mallory (1886-1924; remains finally found on the North Side in 1999) still put it best, "Because it is there." The risks are, however, still beyond our imagination.

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