I'm almost 57 and I went from no glasses straight to bifocals at age 42. I had a cervical fusion done two years ago due to a herniated disk in my neck. (This seems to be a job hazard of being a surgeon.) I have trouble tipping my neck back to use more of the lower part of the lenses. I have the seg height, or segment height, of my glasses set higher than normal at 26mm. This helps me focus on the job at hand in the OR without craning my neck forward or tilting my head back as much. That helps substantially at work and at the range.
I put TFX sights on my Shield and XDm Compact. They work for me.
I tried Trijicons on my VP9 with the big orange front dot. It's so big I can't see the target. The rear sight is essentially blacked out during the day and thatt's not my cup of tea either. I ended up switching to the cheaper Trijicon sights but the tritium vial popped out of the front sight during the first range trip after putting them on. I'm trying to decide whether to get TFX or Mepro night sights for that gun.
And now, to the point of my post...
No matter what part of the lenses I use to view the sight, the front sight AND the target are double if I try to keep both eyes open. Heck, if I look at a digital clock across the room with my right eye and no glasses the numbers are double. Try to explain that one (hint: it's astigmatism). Probably a brain tumor or something lol. I've given up on trying to aim with both eyes open. I've come to embrace shooting with my left eye closed. I get much more accurate results that way. I don't care that all the internet experts say that's bad in a defensive situation, losing peripheral vision, can't see what's around me, blah blah blah. If I need to use my gun in a defensive situation my target is going to be squarely in front of me, not off to the edge of my field of view. I just don't buy the argument. The chance of having multiple targets, with one in my peripheral field that I can't see because one eye is closed is absurdly miniscule.
For that matter I also don't buy the internet ninja **** that I need a rear sight capable of one-handed slide racking. That situation just ain't gonna happen. Show me documentation of a CIVILIAN dying because they couldn't rack their slide one-handed and I'll THINK about reconsidering. I have a better chance of winning the lottery, and I don't even buy lottery tickets. But I digress.