I am curious about cataracts.

My mother-in-law, who is in her 80s, had cataract surgery a few years ago. My mother, who is in her 70s, has not had it yet. Is there a specific reason why cataracts develop? It seems unrelated to vision. Also, how should post-operative care be managed after cataract surgery? I didn't know much about cataracts and thought they only occur with presbyopia, but it seems not everyone develops them.