I have a pair of prescription surf shades ( http://surfshadesusa.com/
) that I sometimes wear. They tend to fog a lot though and my eyes are such that I can get by without glasses.
I also chose yellow polarized lenses because where I kite (Canada) often I'll be out in low light situations and the yellow work wonders in low light. Unfortunately the yellow don't help any with the bright sun (aside from the UV protection).
They cost $300 but I was able to expense $200 of that. I don't think I'd spend $300 on them but for $100 they are nice to have. I also use them for other sports than just kite or SUP, they work just fine on land.