Even people who normally wear prescription lenses should have a separate pair of sunglasses with not only a tint for comfort, but an ultra-violet block coating to protect their eyes from sun damage.
Ultra-violet radiation has been shown to cause or worsen a range of eye conditions, including pterygia, cataracts and age-related maculopathy, as well as making the delicate skin around the eye more prone to lines, wrinkles and skin cancers. Although many of these conditions don't appear until much later, the damage is actually done while you are young, so NOW is the time to start taking precautions.
Your choice of UV protection depends on your vision needs.
Non-prescription sunglasses should meet Australian Standards. This is a compulsory standard and the sunglasses should be labelled as complying with this. Price is not always a good indicator!
Prescription sunglasses are important for anyone who needs a vision correction. They allow you to see clearly and comfortably without squinting in the sun. Ultra-violet light, though damaging, is invisible, and the protection provided by sunglasses is not related to the darkness of the tint. Instead, it is a special coating on the lens that blocks these rays. Remember when buying sunglasses that very small frames do not provide as much lens area, especially to the side of the frame, and therefore offer less protection.
For contact lens wearers, it is now possible to wear lenses with UV guard built in. Several brands of disposable lenses offer this feature, and conventional lenses are sure to follow. The benefit of these lenses in preventing eye disease is still being studied, but contact lenses cannot protect the conjunctiva (white of the eye) or the skin of the eyelids, so sunglasses are still a must!