Travel Reference
In-Depth Information
erprevents bloodorfluid fromescaping into the retinal spaces. Either decreased oxygento
the retinal cells or leakage of fluid or blood into the retina can cause loss of vision.
High-Altitude Retinal Hemorrhages
High-altitude retinal hemorrhages are disorders that occur at altitude and are discussed
Optic Neuropathy
The optic nerve is also susceptible to damage. This vital connection links the eye to
the brain. Increased pressure in the brain from swelling of the nerve cells, increased blood
volume, and edema is transmitted to the optic nerve. This leads to papilledema, a swelling
of both optic nerves that causes transient blackouts of vision. Obstruction of blood flow to
part of the optic nerve can cause permanent visual loss.
Glaucoma is a condition in which the pressure within the eye is increased because the
secretion of intraocular fluid exceeds resorption. Damage to the optic nerve is associated
with the increased intraocular pressure. The decrease in oxygen at altitude makes the optic
nervemuchmorevulnerabletodamagebyglaucoma.Thus,climberswhohaveopen-angle
glaucomamustbeparticularlycarefulwhenascendingtohighaltitude(acuteangle-closure
glaucoma, which is not related to altitude, is discussed in the “Red Eyes” section).
Acetazolamide (Diamox®) is often taken to treat acute mountain sickness because it
helps the kidneys correct the alkalosis caused by rapid breathing at altitude. It is also a po-
tent drug for glaucoma that decreases the amount of aqueous fluid in the eye. Individuals
with glaucoma should take all their current medications and also consider taking acetazol-
amide when climbing high.
Retinal Vein and Artery Occlusions
Another type of retinal condition for which altitude may increase the risk is occlusion
of the retinal vein or artery. People who have experienced this in one eye at sea level have
been found to be at increased risk for developing the same condition in the opposite eye.
Presumably they are at increased risk at altitude. One mechanism of compensation for low
oxygen at altitude is increased production of red blood cells. Red blood cells are packed
withhemoglobin,whichisthemoleculeresponsiblefortransportingoxygenfromthelungs
to organs and tissues throughout the body. As lungs bring in less oxygen, the body cre-
ates more red blood cells to increase its oxygen-carrying capacity. This results in increased
blood viscosity, essentially thicker blood, which is compounded by the dehydration that
many climbers experience during rigorous activity.
Havingthickerbloodcanleadtomoreocclusiveevents,especiallyinsmallvessels.Ret-
inal vein and artery occlusions can be very serious and can result in transient or permanent
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