Here's another solution. Buy some of the stick-on bifocals from Amazon. They attach to your regular glasses through surface tension from a drop of water. Use a sharp pair of scissors to trim them to size. The lowest power worked best for pistol iron sights.

I cut out a circle about 3/8" in diameter and stuck it to my prescription safety glasses. It's big enough to sight properly and small enough that I can walk around without changing glasses or bashing my noggin into things.

Previously, I used my computer glasses. Perfect for shooting, but I had to change glasses to navigate.