I've seen his lenses get cracked, although not quite like that. Usually they crack in such a way that pieces fall out. Which doesn't really make sense. His lenses are plastic with some kind of mylar-like mirror coating (yeah, even though they're white all the time... Alex Ross draws them as mirrors but it always looks stupid).
So generally you wouldn't think they'd break like that. Ever see those eyeglasses ads where they hit the lens with a hammer and it doesn't break? That's just plain old polycarbonate. The stuff is practically indestructible. You wouldn't want sharp shards right next to your eye if you're fighting supervillains, so you'd probably want to use something like that.