The following are answers to a few questions I received from a patient about UV.

Regarding UV and cataracts…How much more of problem is it at 6,000′ Tahoe, 9,000′ Tuolumne Meadows, or 14,000′ Mt. Whitney?

First off, lets talk briefly about the The Eye Problems Associated With UV and HEV

NOTE: HEV = High-energy visible (HEV) radiation, or blue light. Although HEV rays have longer wavelengths (400–500 nm) and lower energy than UV rays, they penetrate deeply into the eye and can cause retinal damage.

Various eye problems have been associated with overexposure to UV radiation. As an example, UVB rays are thought to help cause pingueculae and pterygia. These growths on the eye’s surface can become unsightly and cause corneal problems as well as distorted vision.

In high short-term doses, UVB rays also can cause “Snow blindness” or photokeratitis, a painful inflammation of the cornea. Severe photokeratitis, can cause temporary vision loss usually lasting 24-48 hours. The risk for snow blindness is greatest at high altitudes, but it can occur anywhere there is snow if you don’t protect your eyes with UV-blocking sunglasses.

Because the cornea seems to absorb 100 percent of UVB rays, this type of UV is unlikely to be the culprit in cataracts and macular degeneration, which instead are linked to UVA exposure.

(BTW: UVC rays are totally absorbed by the Earth’s ozone layer, so not an issue here – yet).

According to a European study published in the October 2008 issue of Archives of Ophthalmology, HEV radiation — is associated with the development of macular degeneration.

Risks of eye damage from UV and HEV exposure change from day to day and depend on a number of factors, including:

• Geographic location: UV levels are greater in tropical areas near the earth’s equator. The farther you are from the equator, the smaller your risk.
• Altitude: UV levels are greater at higher altitudes.
• Time of day: UV and HEV levels are greater when the sun is high in the sky, typically from 10 a.m. to 2 p.m.
• Medications: Certain medications, such as tetracycline, sulfa drugs, birth control pills, diuretics and tranquilizers, can increase your body’s sensitivity to UV and HEV radiation.
• Setting: UV and HEV levels are greater in wide open spaces, especially when highly reflective surfaces are present, like snow and sand.

Which leads perfectly well into the next question:

Is there more UV reflected from snow and water?

UV exposure can nearly double when UV rays are reflected from the snow. See above regarding “Snow Blindness”.

And there is less risk of UV exposure in urban settings, where tall buildings shade the streets.

Surprisingly, cloud cover doesn’t affect UV levels significantly. Your risk of UV exposure can be quite high even on hazy or overcast days. This is because UV is invisible radiation, not visible light, and can penetrate clouds.

We were hiking in the snow at about 10,000′ yesterday. We had dark glasses. How about the dog, he
wouldn’t wear shades?!

Unfortunately, the same applies to dogs.  While canines and most mammals don’t have well developed maculas – their risk for macular degeneration is…well…low.

But these creatures definitely get cataracts and as you can imagine, many pet owners opt to have these lenses emoved.

Perhaps, the more forward thinking pet owners out there will seek the services of places like the this: