I think the situation was partly analyzed above concerning the extra distance the gun is from your body....actually eyes. The guys with young eyes will someday discover vision degradation, unless they are very blessed. I have much, much better target scores one handed, often better left handed (wrong-handed

) than with Weaver stance, and it's mainly due to vision. Personally, I have some vision related problems, and some am currently in the process of experimenting with a new type of contact lenses as a "last ditch effort" to have any type of multi-distance vision. Otherwise, it's the regular hard lenses I had to return to after unsuccessful lasik surgery several years ago, and reading glasses combined (never know what strength glasses I may need during a range session, so I take at least three).
I know there are a lot of ways to compensate for the vision problem: drill with one gun at point shooting, use big dot night sights, ask your "target" to wait until you have a good sight picture, use a shotgun....
Vision imparement has to be experienced before it can be understood!
Just my worthless 2 cents!