Do you wear glasses to improve your vision? Commonly, lenses are ground so that the focal point is placed in the center. They can be ground so the best focus is in the corner to sharpen up the sights. You'll have to find a optomitrist who is a shooter to get them to understand your problem. If your problem is loss of the ability to switch focus, like all us old folks, try focusin' on the front sight exclusively, and leaving both the rear and target fuzzy. A peep sight eliminates the need to align the rear sight with the front, just look through it at the front. The smaller aperatures will help sharpen the front sight, but hardly improve accuracy, so one that allows enough light won't be a waste of effort. :v