system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why can't eyesight fix itself? Bones can mend, blood vessels can repair after a bruise...what's so special about lenses that they can only get worse?

How is it possible to have bad eyesight at 21 for example, if the body is at one of its most effective years, health wise? How can the lens become out of focus so fast?

Edit: Hoooooly moly that's a lot of stuff after I went to sleep. Much thanks y'all for the great answers.
gpt
It can. If your eye is damaged, it will at least try to repair itself. Lenses are usually left foggy afterward, as scar tissue does not play nice with the optically smooth surface needed for a good lens.

If you're referring to nearsightedness/farsightedness, they happen because your body makes the eye the wrong shape. It's exactly how your body thinks it's supposed to be, so it doesn't fix it.