A friend who is a high master and an MD told me to just measure the distance from my eye to the front sight (at home) and ask the eye doctor to set the focus at whatever distance is 7" in front of the front sight. The idea is to have the front sight in focus, even if it's an aperture, and it doesn't matter if the target is blurry. I did this and it's a pretty good idea, though maybe not perfect.
