A lot of people think that "focus on the front sight," means that the front sight must in focus. This is not true. It simply means that you must concentrate your attention on the front sight, and that you must actively look at the front sight to be sure it is lined up properly with the rear sights.
For those of us who are getting older, this often means that we will put the fuzzy front sight over the blurry rear sight, align them as best we can, and press the trigger smoothly.
Don't destroy your solid, good shooting stance that allows you to have a good recoil control, simply because someone told you that you had to "focus" on something blurry. They just meant you should be paying attention to how it is lined up.
Also, if you are practicing for the purposes of self-defense – not just plinking, but planning to bet your life on your ability to shoot the gun accurately when you need it – it is foolish to be getting specialized glasses for the purpose of shooting. You need to be able to trust your own eyesight as your own eyesight will usually be.
pax