The Scientist: Burt W. Dubow, O.D., an optometrist in Minnesota and a fellow of the American Academy of Optometry.

The Answer: Sunglasses work by absorbing UVA, UVB and UVC rays from sunlight, protecting the eyes and the sensitive tissues around them from damaging radiation. They also block brightness so you don’t squint, cut down on glare and increase contrast to help you see things quicker and more accurately. While regular sunglass lenses dampen all light that comes through them, polarized lenses specifically filter out horizontal wavelengths, which create glare, while allowing vertical wavelengths to pass through.

UVA exposure can damage the retina and lens (of your eye, not your glasses), leading to cataracts and macular degeneration. Then there are UVB rays, which can cause skin cancer around your eyes just like it can anywhere else on the body. (Translation: Embrace big frames.) You can also get a sunburn in your eye itself from UVB; the technical name is photokeratitis, or snow blindness. Add to that the wrinkling effect of squinting in the sun all the time and you have more than enough reason to want a decent pair of shades.

Now, there are sunglasses and there are good sunglasses. Ideally, you want polycarbonate or harder-to-break Trivex lenses that absorb 99 to 100 percent of all three types of UV rays. Whether or not you go for polarized lenses is a matter of preference more than protection. They reduce the glare coming off asphalt, sand, water or snow, making it easier to see (and react to) what’s in front of you. Compared to non-polarized lenses of equal quality, though, they aren’t any more effective at cutting down on UV rays.

Many cheap sunglasses have stickers on them saying they block UV. But most of them have poor quality lenses that block some of the light with their color but don’t absorb harmful UV radiation. That can actually make things worse for you, because by making things darker, they cause your pupils to dilate (open wider), letting in even more radiation.

Even on cloudy and foggy days, there’s still UV radiation beating down on you, so find a pair of great sunglasses you love and wear them all the time.

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