Lifespan of sunglasses
02/28/2005 |
Question:
Do the ultraviolet-blocking chemicals in sunglass lenses lose effectiveness with time or cumulative UV exposure? Should non -prescription sunglasses be replaced after a certain number of years even if they appear to be in good condition? I`ve had my current pair (Bolles w/polycarbonate lenses) for nearly five years.
Answer:
Great question!
There are two different methods to provide sun protection for your eyes: one is with ultraviolet (uv) protection incorporated into the ophthalmic lens material. This occurs when you buy polycarbonate (a tough plastic) or photo-chromic (the ones that get darker when you are outside and lighten when you come inside) lenses. Another method is to apply a uv coating on the surface of standard glass or plastic ophthalmic lenses. Both methods should block 99% of the harmful uv radiation that could enter your eye (Note: you may get some direct or reflected light sneaking in from the side unless you have wrap-around glasses).
In the first method, no: uv protection lasts as long as the lens is worn. But in the second method, yes: uv coating can get scratched and eventually be rubbed off, and that severely affects its ability to protect your eyes.
For more information:
Go to the Eye and Vision Care health topic.