Ultra-Violet, UV, is an invisible light that has the power to burn your skin, cornea, lens and retina. Sunglasses and prescription eyeglasses have 100% UV protection. UV light can penetrate overcast skies and 40% of exposure occurs when we are not in full sunlight. The retina is the only internal organ of the body that is exposed to UV light.
Sunglasses keep foreign material from hitting the eye while you are outside. So the safety glasses effect of a protective barrier makes wearing sunglasses smart, too.