You may think we wear sunglasses for comfort and fashion. But here's another important reason to wear sunglasses—to protect the health of your eyes.

If you spend long hours in the sun without protection, you increase your exposure to ultraviolet (UV) rays. UV is an invisible form of radiation from sunlight. Overexposure to UV-A and UV-B radiation causes damage to the skin and eyes. You can damage the surface of your eyes in the same way you can get sunburned—with just one exposure to extremely bright sunlight reflected off sand, snow, or water. Exposure to sunlight over years can lead to vision loss from cataracts or macular degeneration.

According to the American Academy of Ophthalmology (AAO) and the American Optometric Association (AOA), these are conditions that put the eyes of adults and children at risk:

• Surfaces like snow, sand, water, and concrete that reflect UV rays.
• High altitudes or low latitudes. Exposure to UV rays is higher in the mountains or closer to the equator like in the Caribbean.
• Time of day. UV radiation is usually at its highest from 10 a.m. to 4 p.m. As a rule of thumb, check your shadow. If it's shorter than you, UV radiation is at a higher intensity. If it is longer, UV radiation is at a lower intensity.
• Time of year. UV radiation is higher in the spring and summer, or May to August in the northern hemisphere, and lower in the fall and winter.

Protect your eyes:

• Don't look directly at the sun. The AAO and AOA say that damage to eyes from looking directly at the sun during an eclipse is from thermal rays of the sun, not UV radiation. Sunglasses won't protect your eyes. Don't look directly at an eclipse.
• Wear sunglasses that protect your eyes from UVA and UVB rays when you are outside. Wear them even on cloudy days. Ask your optometrist or ophthalmologist for advice on sunglasses that offer a safe level of protection.
• Wear a hat to provide additional protection for not only your eyes, but also your skin. Wear one even on cloudy days.

These safety measures are especially important for people who have lighter skin or light-colored eyes, and for people who take medicines that increase the skin's and eyes' sensitivity to sunlight. These medicines include tetracycline, doxycycline, allopurinol, sulfa medicines, birth control pills, diuretics, phenothiazine, and psoralens.

The AAO and AOA advise against buying sunglasses that promise to block UV radiation but don't say how much is blocked. If they don't block 100% of UV radiation or say UV absorption up to 400nm, don't buy them.

Either plastic or glass lenses can soak up UV light, but the protection of either can be improved by the addition of a clear UV coating. According to the AAO and AOA, mirror coating and gradient tinting of lenses don't offer UV protection. The color and degree of darkness of lenses don't mean the lenses can block UV rays. Polarized lenses block glare, but offer no UV protection. Photochromic lenses, or lenses that change from light to dark when exposed to UV rays, may offer protection. Wraparound sunglasses keep light from shining on your eyes from the sides, offering more protection. Polycarbonate lenses offer 99% UV protection.

For comfort, sunglasses should be free of distortion and imperfection. Look through the glasses at arm's length and move them slowly across, up and down over a square pattern like a floor tile. If the lines sway or wiggle, the lenses are imperfect. You also should check lenses to make sure the color is exactly the same throughout.

If you play sports, consider getting special lenses made from polycarbonate plastic that protects them from breaking. Also, get them with a coating that protects them from scratching.