Keeps out the UV's
These are fantastic glasses. I have tried all the different ones and when I look up, down, left, right along the periphery of my vision, these let in the fewest UVs. When I'm up high on a mountain I don't want to take any chances with my vision. The fit is great too. I have a low bridge on my nose so glasses love to slip down, especially when I glance down to check my footing. The adjustable ear hooks and rubber cinch keep these in place even when my face is sweating. I got the Spectron 4 polycarb lens because I didn't want to risk glass shattering on a fall. The white also looks sleek and cool. Great glasses - highly recommended.