Even if you wear glasses you still need protection from ultra violet rays. Prescription sunglasses are available in a wide range of styles and lenses, including polarised lenses to reduce glare when driving, or around water. There are also frames available with a sunglass clip-on, so you only have to have one pair!
Contact lens users can now wear lenses with UV protection. This stops UV that would go inside the eye, but sunglasses will protect more of the eye and the eyelids.
UV light can cause a range of problems including cataracts, pterygia and skin cancers as well as making the skin around the eye prone to wrinkles from squinting.