Back when I didn't need reading glasses, I worked in a country that had malaria. Didn't want it to affect me so took the anti-malarials daily. Went from brands Niviquin, Paludrin, Maloprim etc, whatever was available and effective at the time. Noticed that when I was above cloud that my sunnies weren't as effective, so when I was out on leave bought a darker pair. Then I read an article about the long term effect that continued use of anti-malarials (they didn't actually stop you getting the 'bug', they just suppress the symptoms) could do to your eyes. So I went off the tablets. Later I noticed my new sunnies were now too dark, so went back to the old ones for a while. Seems the iris had been dilated letting in too much light, but over time again it came good, luckily I never did get malaria (touch wood for the future) while in that environment.
Requiring reading focus after age 41, I initially had small look-over lenses as the outside vision was still sharp, but it complicated the sunnie arrangment. One solution was to have a top section shaded but not magnified, graduated to a clear bi-focal prescription segment at the bottom for reading charts and small print. The really important thing I found, was to sit in the aircraft that was mostly flown, and note where the top of the glareshield cut your line of vision in the normal head level position. If you get the position of the segment wrong when drafting the prescription, then you may have hours of neckstrain, just tilting your head forward or back that little bit to get the outside/ inside reationship right, if you can't adjust the glasses just right.
The trouble with prescription, as always, is that after a year or three, you have to go through the exercise all over again for another set as your eyes change.
One last thing, that has been mentioned, - is the fit of the frame under the headset for long periods. Annoying if you get it wrong there.