In our part of the world it is most important to wear sunglasses because many studies have shown that ultraviolet light from the sun can contribute to cataracts, macular degeneration, and skin changes in the eyelids, including cancer.
Sunglasses should be worn in the summer, especially at the beach or in the water and in the winter when participating in outdoor sports like skiing at high altitudes. Additionally, some medications ( some psoriasis drugs, tetracycline, allopurinol) increase sensitivity to ultraviolet light.
The main factor in purchasing sunglasses (in addition to the cosmetic and aesthetic aspects) is how much ultraviolet (UV) A and B rays are blocked. Even clear glasses absorb some UV light, but certain added treatments to glasses give even better blockage of the harmful rays. The higher the percentage of UV blocking the better (100% is ideal).
Ground and polished lenses in the sunglasses are the best, even in non-prescription eyewear. Inexpensive lenses can cause distortion of images.
Polarized lenses cut down on reflected glare, as in looking at water in fishing and pavement in driving. Polarized lenses need to be combined with an additional chemical to block the harmful UVA and UVB rays.
Wraparound glasses are shaped to keep light from coming in around the frame and can often be combined with your prescription.
Gradient lenses are darker at the top and get lighter toward the bottom and are good for driving to see the dashboard better.
Mirror-coated lenses cut down on visible light, but do not necessarily cut down on the harmful UV rays.
Blue-blockers are the amber colored lenses that give a yellowish cast to objects. It is felt they are good for preventing macular degeneration are and popular for outdoor activities (skiing and hunting).
Patients who wear contact lenses and who have had cataract surgery with lens implants need to check with their eye doctor to see if the lenses cut out the harmful rays.
One pair of sunglasses does not fit every situation, but with the above information, you can get a start.