Originally Posted by MacCool

Different people see the dots on red-dot-sights differently. Some people see a lot of distortion, fuzziness, comma-shape, etc in the dot no matter the magnification or brightness and that variability between people is usually due to amount of astigmatism that their eye's cornea imposes. Some people have so much astigmatism that red-dot-sights simply aren't useable for them, in which case they're better off with a second-focal-plane zoom/magnified optic.

Astigmatism is usually well-corrected with accurately ground prescription lenses. Hint: your 1-hour budget lens grinder at your local mall is usually not the best place to get accurately-ground corrective lenses.