If I focus on the ring in this image (the ring is 1 cm tall on my monitor, I stand 300 cm away, the room is dark, and I cover one eye), I actually see an "8" formed from double-vision where the lower ring is dimmer. So, I'd simply say that this lower ring is caused by a cataract.
To be honest, the "cataract ring" is not just lower, but also slightly right; the off-vertical angle is roughly 20 degrees. It's interesting that my other eye also has similar downward double-vision (with a smaller 10 degree rightward shift). (I get even more cataract glare details when I focus on the small dot to the left, instead of the ring, but I'm trying to keep this question simple.)
Do most people have downward double-vision in both eyes like me? If so, is there any theory about why/how the eye changes asymmetrically as we age? I guess that the exact statistical study I'm suggesting here has never been done, but hope cataracts have been studied enough to answer theoretically.
