Can sunglasses lose uv pprotection over time?

[English]

Since most of us wearing sunglasses is for UV protection to eyes. But i wonder if sunglasses lose uv protection over time? How often should we change our sunglasses?

[Englishtown]

I never find there is a research associated with such questions. And there is no evidence that proves whether sunglasses lose UV protection over time. But personally, I heard the sunglasses can prevent UV rays because of the UV coating on the lenses. So, i believe that the sunglasses won't lose UV protection unless you damaged their UV coating.

[Enhaut]

Maybe. More than 90% ultraviolet rays will be filtered by the coating film of sunglasses. But this kind of function will be deduced if the films suffer by scratching. So coating film can not be touched by organic solvent or hard objects to protect the coating.