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I am fairly short-sighted and wear glasses pretty much all the time. Naively, I would expect that when I take my glasses off, the image I see should look very much the same as as a photograph that's out of focus, or an image to which someone has applied a Gaussian blur filter. In bright conditions this is mostly true, but at night if I look at distant point sources of light, the blurry halos around them appear to have quite a complex structure, and a fairly well-defined edge. Why is this?

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This isn't an answer, just speculation. In dim light, your rods are primarily responsible for perception (cones don't work very well). Cones are also more concentrated in the center of the retina, which would mean that rods are more concentrated at the edges. Something to do with focusing in nearsighted people might explain this. –  dd3 Apr 6 '13 at 15:51
    
dd3's suggestion makes sense to me but I wonder if you could add a short paragraph to explain the 'structure' a little more? –  daniel Mar 14 at 19:35
    
@daniel I'm not sure if I can easily describe it in words. If I get a chance some time I will make a sketch. –  Nathaniel Mar 15 at 2:17
    
@Nathaniel Could just be refraction playing tricks on your eyes. –  The Last Word Jun 4 at 5:20
    
@Nathaniel or could be floaters. en.wikipedia.org/wiki/Floater –  The Last Word Jun 6 at 5:05
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