Which Type of Sunglass Lens Blocks the Most Light?

Gray-tinted, wraparound sunglasses that provide 100 percent ultraviolet (UV) protection block the most light. Darker glasses cause distortion of certain colors and dilation, allowing the entrance of more damaging rays. Without this total UV protection, your eye's cornea, lens and retina can be damaged by UV radiation. Eye problems that can result include cataracts, glare, light sensitivity, increased near-sightedness, benign growths on the eye's surface, macular degeneration, snow blindness or skin cancer on the eyelids and around the eyes.

Clarifying Confusion

• Look for sunglasses with labels that say "100 percent UV protection" to block the most light. However, be aware that many labels are misleading, according to the American Optometric Association. Have your potential purchase checked by an optometrist for its protection against both UVA and UVB rays. Polarized lenses reduce reflected glare, but they don't block UV rays. Polycarbonate lenses are designed to reduce the impact of a blow to the glasses, but they aren't a substitute for sports safety or occupational eye wear protection. Certain contact lenses can provide extra UV protection. Scratches on lenses do not just look bad, but they also scatter incoming UV rays and cause glare.

Sunglass Style

• Wraparound sunglasses block light from entering the sides of your eyes. In addition to looking more fashionable, they also offer the best protection from developing skin cancer of the eyelids.

  High price, however, does not equal high quality. Studies have shown that some higher-priced sunglasses have inadequate UV protection or poor quality lenses,

  while some lower-priced lenses rank well in both categories, according to the American Optometric Association website. Wear a cap or a hat with a wide brim for extra eye protection. Wearing only a hat blocks about half of the UV rays.

Degrees of Darkness

• Darker sunglasses do not offer the best protection. They can distort colors such as the red and green of traffic signals. They also can cause your eyes to dilate, allowing in more damaging sun rays. To see color without distortion, especially when driving, the best lens color is gray.

Gradient Tints

• Check the uniformity of the tint to be sure it is not darker in one section of the lens than another. The tint in gradient lenses should lighten gradually from top to bottom. Photochromic lenses darken or lighten with the amount of available light, but that transition does not occur instantly when you move from outdoors to indoors. Car windshields also interfere with the darkening process, reducing the effectiveness of photochromic lenses.

Distortion Check

• Check sunglasses for distortions by holding them at arm's length. Use a straight line in the distance as your guide. As you move the lenses slowly across the line, note whether the straight line moves, sways, curves or distorts.