Updated May 10, 2013.

When shopping for sunglasses, many people tend to look at fashion first, rather than function. While it's always fun to pop on a fresh pair of uber-cool shades, keep in mind the most important reason for wearing them in the first place: to protect your eyes. Ultraviolet radiation (UV rays) from the sun can be very dangerous, sometimes causing irreversible damage to our vision. To properly shield your eyes, you must wear the right type of sunglasses, since wearing the wrong type can cause more damage than wearing no glasses at all.(Tinted glasses lacking UV protection may cause more harm to the eyes than wearing no glasses.) With that in mind, here are a few things to look for while shopping for those new shades.

• UV Protection: Studies show that UV radiation can accelerate the development of cataracts. The bright sun can cause pinguecula and pterygium-benign growths on the surface of the eye. UV radiation can cause cancer of the eyelids and the skin surrounding the eyes. UV radiation can also cause photokeratitis, a temporary but painful burn on the cornea, the clear dome-like structure on the front part of the eye. Photokeratitis often occurs while water or snow skiing without sun protection. Studies also show that long-term exposure to the sun's harmful rays may contribute to the development of macular degeneration. At the very least, you should look for sunglasses that block at least 99% of both UV-A and UV-B radiation, and screen out 75-90% of visible light.

Tinted Lenses: Lenses may be tinted in several different colors. Your choice of color may depend on a combination of style and purpose. For general use, the colors green, grey, yellow, or brown are recommended in order to minimize color distortion. Gray is a popular choice as it allows us to recognize and perceive colors more naturally. Brown and green lenses tend to enhance contrast. Red lenses cause significant color distortion but are good for low-light conditions. Orange and yellow lenses have excellent contrast enhancement and depth perception, but tend to distort colors. (Yellow lenses tend to be a favorite choice of golfers and shooters.) for its contrast enhancement and depth perception properties. Blue or purple lenses are chosen mainly for style and fahion purposes, as they offer no real benefits to vision.

Polarized Lenses: Most quality sunglasses have polarized lenses. Keep in mind that you don't have to have a polarized lens to block out UV radiation. However, most people are much more comfortable wearing polarized lenses, as they do an excellent job of blocking reflections and glare. People who work outdoors in the bright sunlight enjoy polarized lenses. Polarized lenses also allow fishermen to see deeper into the water.

Photochromatic Lenses: These lenses darken or lighten when entering into bright sunlight. Upon returning indoors, the lenses return to a clear state. Photochromatic lenses are an ideal choice for those not wanting to carry a separate pair of sunglasses along with their regular eyeglasses. However, most brands of photochromatic lenses do not darken completely inside of cars, making them less effective sunglasses. For those who prefer a dark lens inside the car, a separate pair of sunglasses may be necessary.

Polycarbonate Lenses: Polarcarbonate lenses are among the most impact-resistant lenses available, providing protection for people who need to wear sunglasses while enjoying sports or other hazardous activities. These lenses won't shatter like glass lenses or regular plastic lenses. Polycarbonate lenses are especially tough but scratch easily. Be sure to look for ones with scratch-resistant coatings.

Buyer Beware: Keep in mind that no federal sunglass requirements exist regarding the amount of UV light blocked by sunglass lenses. However, the American Optometric Association recommends that sunglasses block at least 99% of UV radiation. Also, there is no uniform labeling of sunglass products as to how much UV radiation is actually being blocked. Labels can be quite misleading, so read them carefully. Many opticals have an instrument that can measure the amount of blocked UV, so if you are concerned about a particular pair of sunglasses, this may be a viable option.

<sub>Source:

Pamphlet: Shopping Guide for Sunglasses, 243 N. Lindbergh Blvd. St. Louis, MO 63131. American Optometric Association, 200.</sub>