Rangefogger? I'm in the same boat as you, except that my dominant eye has been stuck at 20/100 since my teen years due to an injury. Lots of good advice in this thread. Shooting with both eyes open is obviously the ideal, but everyone's eyes are different and not everyone can manage this, even with practice. For me, it depends on the sights. I can shoot both eyes open with modern sights, and even some aperture sights if the aperture is large enough and close enough to my eye, but the tight notches that are commonly found on muzzle loaders? No way in heck.
Your best bet is to probably get the glasses, but I have a trick that hasn't been mentioned that might work for you. As a young enlisted man, I was required to qualify on a variety of firearms, and some of them had iron sights that didn't play well with my vision; my dominant eye was good enough to pick up the front sight, but most targets would be lost in the blur, and because of the mismatch between my two eyes I couldn't always shoot with both eyes open. My workaround was to line up on the target with both eyes open, close my weak eye so that I could clean up the sight picture, and then fire when my sights were aligned on where I knew the target was. (Even though I couldn't technically see it anymore.) If the target was moving or the sight picture fell apart, I'd reopen my weak eye again to reaquire. It's a bit difficult to describe, but remember that your weak eye can be open or closed almost instantaneously if necessary.
This is a bit unorthodox and not something that I normally taught, except to students with severe vision problems that couldn't make anything else work. Sometimes it helped. It may or may not in your particular case, but it allowed me to hold well enough for "E"'s when I otherwise would have had problems even hitting the target at all, let alone the bull. Obviously this method is a bit slower than the others mentioned, but regular practice can reduce the time lag to an insignificant amount.
