I actually just had this happen for the first time 2 weeks ago. It was really weird. I had my head turned at a really restrictive angle for about 1 minute and about 5 minutes later, no matter where I looked, there appeared to be a "tear" (like a rip, not a tear drop) in the scenery. Inside of the "tear" there were jagged lines all parallel to each other, different colors (black, orange, and green) and flashing. I thought it was like seeing dots when the blood has been restricted to your head, but then it got bad enough that I was having a pretty serious gaps in my vision in both eye (I could only see/read from the side of my eyes). Anyway, I was a little freaked out, so I googled "seeing zig zag lines from eye" and came up with a bunch of sites. Like someone said, it was an opthomalic migraine, and judging from the large number of google hits, it seems relatively common. Anyway, I was relieved and it went away after about 5 minutes.