Eyes can only focus at one distance at a time, you cannot focus on the rear sight and the front sight at the same time, let alone one or both of these and the target at the same time.

I'm nearsighted also, but I have amuch easier time seeing the front sight of a rifle than the target. Without my glasses on, a 6 inch bullseye at 100 yards looks like a fuzzy blur, with my glasses on it looks a bit sharper if I strain real hard, but this doesn't help my shooting. If you focus on the front sight and hold on your target with the same sight picture whether the target looks like a sharp circle or a fuzzy blotch you will shoot well. A rear aperture sight will help alot with the sight picture. Some of the best shooters I know are old farts who have no right to be able to see anything smaller than a volkswagon at 100 yards yet can still pull off amazing shooting with iron sights because they use a consistant sight picture.

Alcohol, Tobacco, and Firearms... who's bringing the chips?