Hi,
Your optometrist can tell you what diopter of optical correction you need if you tell the focal length.
*Assume your usual shooting stance for practice.
*Measure the distance from your eye or spectacle lens to your front sight.
*Ask what diopter correction to use.
*Option A: You can have special shooting glasses made (polycarbonate for impact protection) perhaps, even putting the "shooting correction" above your distance correction, so that when you tilt your head to aim or make cheek weld, you are looking through the needed field.
*Option B: Buy simple reading glassses at the drugstore in the desired strength, add safety goggles over (hardware store) for eye protection. This is fine for informal or range practice. Option A may be better for active duty/activity or hunting and can provide other near and far correction if needed unpredictably.
*Your optometrist will not be upset by this question.
*You may find a single correction, or bi-focal for reading, like this suitable for long use at the computer monitor.