Let me give you an exercise that may delay the need. This was given to me by an opthamologist a long time ago and it helped for years. Hold a pencil at arms length, focus on it with both eyes and bring it slowly to your nose while maintaining focus and then take it back out slowly-still focused. Repeat numerous times a day and your focus should improve or at least hold your own. !.5 is not a lot of magnification, but you may not recover all even with the exercise. It worked for me for a good many years then I got lazy and stopped. Things soon went to pot.
In shooting iron open sights there are three things to look at and even those with perfect vision have to choose what priority the want to have in perfect focus. Always choose the front sight, rear sight, and target in that order. If you see the rear sight, and have a perfect focus on the front, the somewhat blurred target will not matter so much. Peep sights take the rear sight out of the equasion and optics allow you to see the reticle and target equally-if the optic is properly focused. I can no longer focus up close, but a slight correction in the top of my trifocals does help both irons and optics. Be sure to get a shattreproof lens if you go glass.. jack