Denver sits at about 5,280 feet, which is why it is called the Mile High City. Coloradans tend to think about sunscreen at altitude. Fewer think about their eyes, even though the same thin air that makes a sunburn come on fast also lets more ultraviolet (UV) light reach the eye.
What the numbers say
The World Health Organization’s Global Solar UV Index guide, written with the World Meteorological Organization and others, explains why:
- Altitude. With every 1,000 meters (about 3,280 feet) of altitude, UV levels go up by about 10% to 12%. At Denver’s elevation, about 1,600 meters, that works out to roughly 16% to 19% more UV than at sea level. Ski areas at 9,000 to 11,000 feet are higher still.
- Snow. Fresh snow can reflect as much as 80% of UV radiation. Dry beach sand reflects about 15%. That is why a bright day on the slopes delivers UV from above and below.
- Clouds. UV is highest under clear skies, but even with cloud cover it can still be high.
What UV can do to eyes
A short, intense dose can cause photokeratitis, often called snow blindness: a painful sunburn of the cornea that shows up hours later with gritty pain, tearing and light sensitivity. It usually heals in a day or two, but it is miserable. Years of exposure are linked to cataracts and to growths on the surface of the eye, such as pinguecula and pterygium.
Simple habits for high-altitude days
- Wear sunglasses or goggles labeled to block 99% to 100% of UVA and UVB. Wraparound styles block light from the sides.
- On snow, wear goggles or glacier-style glasses, even on overcast days.
- Add a brimmed hat for hikes and summer days in Washington Park or Red Rocks.
- Do not forget kids. Children spend more time outdoors and often skip sunglasses.
- If your eyes are painful and light sensitive after a day on the snow, see an eye doctor.
Denver is a long way from our office in Westlake Village, California, but sun safety is the same everywhere: shade your eyes the way you protect your skin.
Source: Global Solar UV Index: A Practical Guide (World Health Organization, WMO, UNEP and ICNIRP, 2002). This article is an educational summary written by Khanna Vision Institute and is not a substitute for medical advice.