In reply to anon60521: category 4 lenses. I used normal oakleys for 3 weeks on my first trip out and ended up with itchy eyes some days which was not too pleasant.
its worth taking a pair of cheap goggles in your sack in case it gets seriously windy and blizzard like but i've only found this necessary at 4000m+.
in terms of brand I use julbos which are great. plenty of protection and they don't let to much wind through either although they do sometimes steam up over prolonged front pointing or serious exertion but clear up very quickly. they also look like a pair of normal sunglasses which makes all the difference when having a post climb beer. theyre not too pricy either and as far as i can tell, pretty tough.