Incredible. I could never find a name for that. I used to have it in early 2Ks. I also had weird brain issues[1], and also have many floaters so I just thought it was one placed just in the worst place, causing refraction. It usually started as a small patch that gradually stretched, moving along the outer edge of my vision. As Wikipedia says, the migraine came a little after that. The last 3 pictures in the article are quite on point : http://en.wikipedia.org/wiki/Scintillating_scotoma

ps : Many thanks

[1] As far as I could search, it's close to sleep epilepsy.