[Old Jim]

DOK and I have been talking about this very thing off the forum.
I wear trifocals. The trifocal slot gives me good sight clarity with a fuzzy target. I tried a poor-mans shooting glasses trick of buying a cheap($10) pair of reading glasses from Wally World that focused at about the front sight. Since my distance vision is still pretty good, I knocked the left lens out, thus giving a right eye focused at about 3.5 feet and the left eye with no correction. You would not believe the severity of the instant headache. May work for some people but not for me.
DOK also suggested a pair of clip on sunglasses with a tiny aperture drilled in the lens material. This helps but not enough to pursue it for me.
I have tried the peepsights but tend to string shots verticly with them.
DOK also has tried an add on lens that sticks to the front of your regular glasses with some success.
This is not a modern problem, by the way. Several antique muzzle loaders have been found with multiple rear sight dovetails. As the eysight failed the owners had the dovetails recut moving the rear sight farther away from the eye

Good luck!!!!

 

[Old Jim]

I just finished a project in which I had to use a 1/16" drill bit.
Being the klutz that I am I bought several so I had one left.
The next day I happened to run across the clip-on sunglasses with the 1/8" hole drilled in them that was done in an effort to make the revolver sights more visible. The light came on!
I drilled a 1/16" hole in a small piece of black plastic, hot glued it over the existing hole and "voila", It works.
My sights are clear and so is the target.
Now I have to shoot a lot better because one of my excuses is gone.