I use these:
They are designed for use in water (they float). Because they float they are light as hell. I use them for kitesurfing and absolutely love them. They totally protect your eyes in really bright conditions. Used them on Kili and Aconcagua.
The best part is that they are cheap since inevitably I always lose expensive sunglasses. You can buy 3 for $99 dollars on their website. I've never broken a pair despite tons of terrible crashes kitesurfing.