If the think about if most (if not all) anime characters would be blind by the time they were 20.

Think about it half of anime girls/ guys have eyes that take up half of their faces, and the amount of light that would enter their pupils daily would (over time) weaken the cornea and put a lot of strain on the nerves in their brains (especially if they had light eyes) which your more pron to bad eye sight as it is. Image when your eyes are three times normal size, or image looking into direct sunlight with dilated pupils. That fuckin' hurts! they would have to wear sunglasses everyday!