Photochromiclenses are available in nearly all lens materials and designs, including high indexes , bifocal and progressive. An added benefit of photochromic lenses is that they shield your eyes from 100 percent of the sun's harmful UVA and UVB rays. Because a person's lifetime exposure to sunlight and UV radiation has been associated with cataracts later in life, it's a good idea to consider photochromic lenses for children's eyewear as well as for eyeglasses for adults. Modern photochromic lenses tend to be plastic and instead of silver chemicals they contain organic (carbon-based) molecules called naphthopyrans that react to light in a slightly different way: they subtly change their molecular structure when ultraviolet light strikes them.
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