The key is to get the highest UV protection and nowadays you can get 100% UV protection and that does not have to be super expensive either as under $20.00 will get you a pair. From there it is all about style and construction. I found this snip at an opticians website….
Typically, most sunwear lenses will be UV absorptive to some degree. If lenses are marked CR-39R plastic, about 88 percent of UV light is absorbed. If sunglasses contain polycarbonate lenses, UV absorption will be 100 percent.
All better quality non-prescription polarized sunglasses sold through optical stores are 100 percent UV absorbing. For the very inexpensive polarized sunglass — thin, bent sheet polarized types provide UV absorption. Lenses that are polycarbonate are usually UV absorptive. However, many cheap sunglasses use a material called triacetate. This material absorbs only about 40 percent of the UV rays. Lenses may also be made of other acrylic materials, which will vary from partially to fully absorbent.
To know that your lenses are 100 percent UV absorbing, purchase them from reputable companies, specialty sunglass stores or from an optical professional. Typically, most sunwear lenses will be UV absorptive to some degree. If lenses are marked CR-39R plastic, about 88 percent of UV light is absorbed. If sunglasses contain polycarbonate lenses, UV absorption will be 100 percent.
All better quality non-prescription polarized sunglasses sold through optical stores are 100 percent UV absorbing. For the very inexpensive polarized sunglass — thin, bent sheet polarized types provide UV absorption. Lenses that are polycarbonate are usually UV absorptive. However, many cheap sunglasses use a material called triacetate. This material absorbs only about 40 percent of the UV rays. Lenses may also be made of other acrylic materials, which will vary from partially to fully absorbent.
To know that your lenses are 100 percent UV absorbing, purchase them from reputable companies, specialty sunglass stores or from an optical professional. — Mark Mattison-Shupnick, master optician