At 32, my vision is now estimated at 20/4000 (no, there are no extra zero's mistakenly added on there) and I'm just now starting to have problems with astigmatism. Best thing for me is to shoot 2-1/4 format with a prism finder. Because I shoot rapidly moving little people as my primary business, I have to be able to manually focus very quickly. I'm finding that I just have to concentrate a lot more than I used to, but I can still do it.
Still, I'm realistic enough to be glad I enjoy teaching workshops, because at some point it's very possible I won't be able to do children's portraiture anymore. Best to have a backup plan.