Price is not the best predictor as to how well sunglass lenses block ultraviolet light. Some expensive, designer shades don't provide good protection, while many inexpensive shades do. When you buy, make sure the label says that the lenses block 100 percent of UVA and UVB rays.

Children's eyes need sun protection just as adults' eyes do.

Read more about pingueculae and pterygia.

Read more about cataracts and age-related macular degeneration.

UV exposure increases at higher altitudes because the Earth's atmosphere is thinner, and its ozone layer is therefore less effective at blocking ultraviolet radiation than at lower elevations. According to the National Weather Service, the altitude-related increase in UV exposure is approximately 4 to 5 percent for every 1,000 feet ascended. So, for example, for the same day in June, you would be exposed to roughly 27 percent more UV rays in Flagstaff, Arizona, than in Phoenix (an elevation difference of about 6,000 feet).

Haze and clouds don't prevent UV rays from reaching your eyes. UV is invisible radiation, not visible light.

Dark sunglass lenses filter more visible light than lenses with lighter tints, but that doesn’t mean they block more UV. The amount of UV protection provided by sunglasses is determined by the lens material (and sometimes a UV-absorbing lens treatment), NOT the darkness of the tint.

HEV, or high-energy visible light, is in the visible light spectrum and is therefore not in the ultraviolet range. It is suspected as a cause of age-related macular degeneration, so certain sunglasses are designed to block HEV light.

Though people with light-colored eyes may be somewhat more at risk of UV-related eye damage, people of any eye color can benefit from UV protection.

Gray is considered the most neutral of lens tints when it comes to color perception.

Don't stare at the sun, because it will damage your retinas, even if you're wearing sunglasses.

Because you want less sunlight entering your eyes when wearing sunglasses, there is no reason to have anti-reflective coating applied to the front surface of sunglass lenses. Light reflecting (away from your eyes) off the front surface of the lenses reduces the amount of sunlight entering your eyes, which helps reduce glare.

But sunlight that reflects off the backside of sunglass lenses when the sun is behind you can enter your eye, causing glare and eye strain. Anti-reflective coating applied to the back surface of sunglasses eliminates this "back-scatter" problem, so AR coating is recommended for the backside of sunglass lenses only.

The UV Index was developed by the National Weather Service and the U.S. Environmental Protection Agency in 1994, based on a similar index developed two years earlier in Canada. The UV Index provides a daily estimate of solar UV intensity to help you plan your outdoor activities and prevent overexposure to the sun's harmful rays that can cause sunburn, skin cancer and cataracts. The index estimates solar UV radiation risk on a numerical scale ranging from 1 (low risk) to 11+ (extreme risk).

After green come the colors yellow, orange and red, with violet representing the extreme risk level of 11+.

UV-blocking contacts can protect only the parts of the eye that are directly behind the lenses. Surrounding eye tissues will still be exposed to the sun.

One example is diphenhydramine, found in the antihistamine Benadryl. Others are tetracyclines, malaria medications, NSAIDs, acne medications and certain antidepressants. There are many sun-sensitizing medications, so be sure to read the label of any drug you take.