I have had these for many years, always lasting around 20 to 30 minutes, on average 2 a month, sometimes 2 in a day, rather scary each time. It can be one eye, or both eyes, if I shut my eyes I still see the zig zags. I have after all these years never found a pattern.
I had a brain scan 2 years ago after deciding they must have damaged my brain after all this time... it was completely normal! The neurologist told me just to get on with it and remember that each time I come through it, and continue with normal life till the next time.. this helps me a lot.
Google the migraine summit, there is a lot of useful information here.