Most bullseye shooters, rifle and pistol, want the front sight as clear and crisp as possible. The target can be a bit fuzzy and still produce excellent results. That's with a target at a known distance, a black bullseye against a white background ... plus the target doesn't move. The target number board may be fuzzy at 600 yds or 1000 yds but still clear enough to shoot on the correct target.
A hunting situation is different in that you need to clearly see the game, at least well enough to know what it is! The instructional diagrams show the rear sight, front sight, and target all in sharp focus. Few people have eyes that have a depth of field from 30" at the front sight to 21,600" at 600 yards. You might surprise yourself at how well you can hit a fuzzy target with a somewhat fuzzy rear sight but a sharp, crisp front sight.
FWIW. as some previous posts have noted, my optometrist allowed me to bring my rifle to his office.