And another great question!
People used to think that getting old meant that you would gradually lose your eyesight. Actually in the modern world there is no need for this to happen, and there are all sorts of treatment options now (like laser surgery) to help people have perfect eye sight. However, there are SOME reasons why sight might get worse with age,
There are 4 things involved in sight
1. The cornea in front of the eye is the “window” that all light has to pass through.
2. The lens receives light, and then focuses that onto the
3. Retina which is like a camera, and light is converted into a signal that the brain can recognise as an image
4. The optic nerve, which carries signals to the brain
So there are 4 ways that our eyesight might get damaged which is more likely the older we are, because we are exposed to more potential damage
The cornea might get damaged on its surface (like getting scratched with grit) and problems producing tears might mean the surface of the eye gets dry. The lens can get cataracts with old age, and also becomes less flexible meaning when you see an older person who has to hold a book much further away from their eyes to be able to focus on it. Luckily these problems can be helped or even cured now!