I have an acquaintance that started having Zig-zags at about age 50. They seemed to take over when she stopped having [roughly monthly] very bad headaches. The early ones were called, by various people, ‘Menstrual migraines' for obvious reasons, but I was never sure that this was a correct term. The later ones cause almost no inconvenience.
A word of caution though. At the time of the Zig-zags, there may be some patches of blindness which are hard to detect. Great care must be taken to test for such blind areas, which of course will travel. I suggest increasing the scan frequency while driving or flying.
http://www.intelihealth.com/IH/ihtIH...80/366022.html