After wearing no-line bifocals for several years my optometrist suggested I try a reading lens in one eye and a distance lens in the other. I am right handed and the distance lens was in my right eye. On my first trip to the range, I discovered my cross hairs were not clearly focused. I held the rifle to my left side and bingo, a perfect picture through the reading lens. I couldn't seem to get the eyepiece as clearly focused for the distance (right lens). The focul point of a scope's picture is close up, so a reading lens was better for me.
That fall while sitting in a deer stand, I had the bright idea to switch my lens to wear the reading lens in my right eye. This immediately confused my brain and I became dizzy and had to switch back. I gave up and switched back to no-line bifocals.
Anybody else with "maturing" eyes have problems attaining crisp sight pictures.