Really bad eyesight, can I prevent it from getting worse?

Likely not so bad. All people with bad eyesight tend to believe theirs is the worst case on the planet. Usually not even close. There is no way to stop eyesight which is due to a need for eye glasses. You need to be sure your bad eyesight is not from a correctable problem so have your ophthalmologist evaluate your eyes and advise you what is the best course of action.