There are correctional eye pieces that fit over the viewfinder.
D-SLR Camera Accessories from Nikon | DSLR Video Accessories & More. I sure Canon also have them if you don't shoot Nikon. I'm not so sure about any other company though.
Just get whatever correction level you need. EX. +2.0 or -2.0. You eye doctor can help you get the right one you need.
Didn't know that; totally checking into that! Thanks! I wonder just how "corrective" they get though? The little diopter adjustment on the side of the viewfinder is completely useless to me--I can't even tell it's been changed from one extreme to the other.
OP: I too have vision problems. Without my glasses, anything more than about 3-4 inches from my face becomes blurry; even with my glasses, my vision just can't be completely corrected. To make matters worse, I have one of the worst cases of "floaters" my eye doctor has ever seen. I have dozens of them, floating in all directions, all the time--they basically serve to make everything LOOK blurry even though it's close enough to focus on. Sometimes it doesn't bother me too much and I can work around it; other times, I really just can't tell whether anything is in focus or not.
Despite that, I think I do reasonably decent with my photography, and I've definitely improved over the last year, so there's hope!
Here are some things I have found that at least help minimize the problem for me:
1. STEADY the camera. Take steps to make sure you hold the camera as steady as possible to minimize any additional focus issues from camera shake. Unfortunately, I also have a hand tremor, so this is also kinda tricky sometimes.!

--I'm just a mess!!
Use a tripod or monopod when possible. A monopod is next on my list of things I really need to acquire.
2. Good glass. It won't exactly "override" your vision problems, but it will give you the best chance of the clearest, sharpest images, and if you have vision problems you need all the help you can get!!
3. Learn what "sharp focus" looks like TO YOU. Take a picture that you THINK is sharp and clearly focused; post it here for C&C specifically about that issue. Do NOT ask your friends and family about it, because if FB teaches us anything, it's that most people evidently just LOVE blurry photos as long as they were taken by a friend or family member!

Do this enough times and you will start to develop a sense of whether a picture is truly well-focused or not. I have a reasonably good idea now, with my own photos of how they look TO ME when they look sharp to others. The more familiar the subject, the better I am at gauging whether it's sharp (that is, if it's something I've photographed plenty of times before, like birds, I've learned pretty well how to tell if it's focused. If I'm shooting something I don't usually do, like maybe a concert--well, they'd probably ALL look out of focus to me!)
4. Learn to use your equipment and then trust it to work--but take extra shots. ;-) The single thing that has helped me the most is to really learn how to use the focusing aids on my camera--focus points, focus lock, etc--then trust them. Despite my vision problems, I *know* where the focus *should* be--for instance, if I'm taking a picture of a person, I want to aim the focus point at the eyes. Then I need to understand DOF and what my aperture needs to be so that I get their whole face in focus, whether I can TELL it's in focus or not. The equipment is going to get the right focus if you set it up the right way and aim at the right place.
5. Relax, and have fun. Do the best you can do and enjoy the results!!