Although the human body is aces at replacing some damaged cells, the cells in the lens of the eye are never replaced. Damage from ultraviolet and (to a lesser degree) infrared rays can build up over a lifetime and lead to cloudy areas on the lens of your eye called cataracts. It's hard to see through cataracts, and they often must be removed surgically. Macular degeneration, an eye condition resulting from damage to the retina, also may be accelerated by too much unfiltered sun blasting the retinas.
This article from the WebMD Eye Health Center can assist you: How to Pick Good Sunglasses Kidzworld helps children to understand the importance of protecting their eyes from a young age: Why It's Important to Wear Sunglasses | 
