ORIGINAL: GRIZZLYMAN
I had to get bifocals several years ago, when I was your age, and I also had concerns. They take some getting use to and I find myself moving my head ever so slightly sometimes to get a good sight picture, but overall, it's not a big issue, at least to me.
the TRI-FOCAL is the best in your glasses at about .50 power.
way you would test it is to buy a .50 from site i rec above,put it over your glasses at the TOP.
then look at your sights and aim at target at 25 yds.
if target is slightly fuzzy, not much and your sights are fairly clear, the front sight should be clear and rear a little fuzzy or clear, THEN YOU NEED A .50 TRI-FOCAL IN YOUR GLASSES.
they dont make a stick-on,that would be cheapest way to do it but they only go as low as a 1.25, THATS NO GOOD, it has to be a .50