For those of us that wear bifocals, getting your iron sights in focus can be a challenge. I just purchased the Gehmann stick-on iris for ordinary glasses. It has made a huge difference in my accuracy. The sights are now clear, and I can see the target, too. I may buy a special pair of glasses with no bifocal, as I don't need to read while shooting. There is, or was a Merit brand, but I can't find any available.
Gehmann Stick On Iris for Ordinary Glasses
Gehmann Stick On Iris for Ordinary Glasses