This is an old thread and my response might well have been discussed elsewhere. However, listening to Tom Gresham the other day, I learned of Optx 20/20 HydroTac stick-on lens. In a nutshell, order the same magnification as for reading glasses. If you aren't sure which one to get, you could go to your eye doctor. Or, you could just go to the nearest Wally World and find their selection of reading glasses. Try reading anything at the same distance for your eye as your average gun or rifle sight. Stick the Optx lens on the lens of your shooting glasses
on your dominant eye side only. Thus, purchasing a pair of the lens gives you one to use and a spare.
http://optx2020.com/p-2-hydrotac-stick-on-bifocal-reading-lenses.aspxFrom experience I can also recommend one trick that is not in the instruction packet because the manufacturer likely did not anticipate use in our endeavor. With your shooting glasses on, assume your normal shooting position. Note with a finger on the outside of the dominant eye lens exactly where you are looking through that lens. Use that location as a guide for accurate placement of the Optx stick-on lens. It is a simple matter to reposition the lens, but that should get you started pretty well.