To effectively protect your eyes from the sun's UV rays, you don't need particularly dark sunglasses or sunglasses with special UV filters.

 

In fact, plastic, even cheap and transparent plastic, is already a UV filter by nature. Therefore, even inexpensive sunglasses effectively filter out UV rays and protect the eyes. The cornea of the eye also acts as a natural filter.

Dark-coloured sunglasses in particular cause dilated pupils and therefore allow more radiation to pass through than normal tinted lenses.