The answer is sooooooooooooo simple: When you renew your glasses prescription, get progressive lenses, and not bifocal. With progressive, there is a place in the lens that allows you to see the sights, although the target is a little blurry, which is okay. That's the way we learned to shoot. Focus on the sights, let the target be blurry. At age 64, with progressive lenses, I can easily tilt my head to where I'm looking through that part of the lens that puts my sights in sharp relief. I can honestly say that my groups from the bench and my hunting success has not diminished since before I even need glasses.
One caution: The last time I got glasses, I bought small, narrow lenses. Even though they are progressive, the area where revolver sights are sharp and clear is much smaller than with larger lenses.
It's true that progressive lenses take some getting used to. For me, it takes about 2 days.
I recently had surgery on my right eye (replacing the eye lens), giving me 20-20 without glasses in that eye. Sometimes when I shoot without glasses, I find myself tilting my head back, looking for that perfect place in the glasses lens that ain't there.
The point is, if your are a pistol shooter, bifocals are useless for that particular endeavor.