correction lens
Several manufacturers make a monocle holder, Anschutz, gehmann, and Centra/MEC, this method is a common option, other wise use shooting glasses.
If you have multiple guns specific glasses are often the preferred options, and they add a degree of eye protection.
BUT, what ever you use, the correction will require a +0.5 dioptre added to your long vision prescription to get the "compromise" correct focal length to 2 mts, as when looking at a target through a diopter sight you have three different focal lengths, and it is impossible to focus on all three.
The rear sight is a small hole or iris, (usually 1.1mm), very close, the fore sight is at a metre-ish, and the target at infinity. The compromise focal length is 2 mts. To achieve that you, with +1.5 plus prescription and with the +0.5 will require a lens of +2.0 dioptre.
This is the correct and standard correction for shooting using a diopter sight, and will allow you to focus sharply on the fore sight (the correct aiming focus) and still see the aiming mark.
Have Fun
Robin
Walther KK500 Alutec expert special - Barnard .223 "wilde" in a Walther KK500 Alutec stock, mmm...tasty!! - Keppeler 6 mmBR with Walther grip and wood! I may be a Walther-phile?