It is more important to see the sights clearly than the target. For best results, I shoot handguns with glasses ground to my reading prescription. I use them when working at a computer too. Ordinary bifocals are awkward, making you bend you head backwards.

Other possibilities are a flip-down peep sight for the shooting eye. The small orifice increases the depth of field (like it does on a camera), so you can see both the sights and target clearly. There are sticky "peep sights" you can put on ordinary glasses. I'm not sure which prescription would work best.