I know how you feel, for I have vision issues as well (patch and all when younger!), and have had glasses since I was 2 years old.
First, huge hugz! I know this is difficult. Second, I agree that pregnancy can change your eyesight, but I do agree that there is more factors involved..(such as age)
As for having another one, and making your eyesight much worse, this I would get another opinion on. I know mine did slightly change after kids, but pregnancy does not normally change your eyesight that much, and if it does--it normally will improve or improve enough to be a slight difference.
To address the concern about pregnancy and your eyes, I would make sure to arrange an eye appointment at the end of each trimester to catch anything early enough to do something about it. That would be my opinion of staying on the safe side of things.
Again--huge hugz--I do understand where you are coming from!!!