Vision correction is tough -- and it's worse because there's no way to know if an optometrist or optician is going to freak out when you mention GUNZ!
In general, the front sight is what's supposed to be in focus, and when shooting the front sight is a few inches beyond arms' length. That happens to be about the same distance as where my computer screen sits, so I just tell the eye docs to set me up for working on the computer.
Annnnnnd ...
They ALWAYS get it wrong. Going back to the optometrist I went to from when I was 14 and he was just starting his practice, right up to when he retired, we always argued about my prescription. Half the time, he made up the lenses the way he insisted they should be, they didn't work, and a week later I was back to have him remake the lenses.
Now that he has retired, I'm having the same problem with the eye clinic at the VA hospital. Six months ago they gave me new glasses with a new prescription. The VA mailed them to my home, I sat down in front of the computer, took them off and never touched them since. I do better with drug store reading glasses than the "professionals" do. I use a 2.25 for reading and computer, and it should probably go up to a 2.5 but I'm stubborn. For shooting, a 1.5 to 1.75 seems to work pretty well.
Some of the dollar stores sell reading glasses. It's cheap enough to pick up a couple or three pairs in different strengths and try them out.