I looked through a Vortex Strikefire II yesterday evening at Academy and it wasn't for me with it's 4 moa dot. Sighted it on ceiling sprinkler heads about 30-35 yards across the store and the dot covered a lot of them up. I think I may have a slight astigmatism too, because the dot was not crisp and had sort of an hourglass shape. When I shot with my friend's SIG Romeo (2 moa dot) last weekend, I didn't notice any of that. I'd say that large dot amplifies a small problem into a big one if it really is astigmatism. It's possible the glass was just grimy (it was a display model, mounted on a dummy rifle, handled a lot), but 4 moa dots may be a problem with my 60 year old eyes. I forgot to do the rotate test while I was looking through it (rotate the sight and see if the dot irregularities rotate with it) to verify if it was the sight or me. I know a prism sight is supposed to work wonders in this area, but the prices are beyond my meager budget at the moment. If you have older eyes, looks like you need to be more choosy.
A little update: I went back to Academy yesterday and picked up a Vortex SPARC II and mounted it on my AR. It was the last one they had, except for the display unit. Considered a SIG Romeo5 at the same price, but this one won out. I've found I do have a bit of astigmatism and that with a 2 moa dot, the flare effect caused by that is far less with the smaller dot. The 4 moa sight I had looked at earlier looked crappy as hell to my eyes. If any of ya'll have semi-old eyes like me, I think a smaller dot is actually much better believe it or not. Haven't shot and zeroed this thing yet, but so far, I am quite impressed with what I got for the money (needed to stay at $200 or less). It's a solid, well designed, nice looking sight and appears to be as rugged as I have heard. I would recommend anybody looking in this price range to have a look at this one. I'll put a pix below to show what these look like.