EYE DISORDERS - Medicine for Mountaineering and Other Wilderness Activities - page 202

vision loss. Individuals who have experienced these phenomena at sea level must use cau-
tion and keep well hydrated when venturing to altitude.
Diabetic Retinopathy
Diabetes is a common disorder in which the body loses its ability to control blood sugar
levels.Oneofthemanyproblemsassociatedwithdiabetesisdamagetosmallbloodvessels
(microangiopathy). Microangiopathy results in capillaries functioning improperly, leading
to oxygen deficiency and nutrient depletion in surrounding tissues. The tissues and organs
that are most affected include the eyes, kidneys, and nerves.
Because diabetes can result in retinal hypoxia and ischemia even at sea level, it is pre-
sumed that diabetics are at increased risk at altitude. Diabetics who venture to altitude ex-
perienceadditionalhypoxiatotheretina,addingtotheeffectofthehypoxiacausedbytheir
diabetes. Although no studies have investigated whether high-altitude retinopathy and dia-
betic retinopathy have a synergistic deleterious effect, it appears likely.Diabetics consider-
ing a trip to altitude would be wise to be evaluated by an ophthalmologist and discuss the
relative risks of their plans.
Retinal Detachment
Retinal detachment is a separation of the photoreceptor layer of the retina from the wall
of the eye. Surgeries to reattach retinas often use gas bubbles to apply pressure that holds
theretinainplace.Sincegasesmayexpandandcontractwithchangesinaltitude,individu-
als who have recently had this procedure should not fly or venture to high altitude until
thegashasdissipated.Althoughnostudieshaveinvestigatedwhetherpeoplewithprevious
retinal detachments are at increased risk at altitude, it is presumed that altitude confers no
increased risk once the retina has been reattached and the gas bubbles have dissipated.
REFRACTIVE CORRECTION
Eyeglasses and Contact Lenses
In general contact lenses and eyeglasses are not good options for outdoor activities at
altitude where oxygen levels are low. Keeping glasses clean and free of fogging in in-
clement weather and cleaning contact lenses sufficiently in an outdoor setting, particularly
at altitude, are difficult. Contact lenses further reduce the amount of oxygen reaching the
cornea,whichcanresultincornealhypoxia.Thisappearstobetheprincipalreasoncontact
lenses are not well tolerated at altitude.
Various types of contact lenses are available. The two most commonly used are rigid
gaspermeable(RGP)andsoftlenses.RGPlensesallowoxygentoreachthecorneasurface
through diffusion and through temporarily moving with each blink, thus briefly exposing
partsofthecornea toambient oxygen.Compared tosoftlenses, RGPsoffertheadvantages
of being relatively easy to clean and maintain, are associated with a lower incidence of