Also, any idea what causes them?

Funny you should ask. I recently saw my opthamologist for the very same thing. Of course, when I went to him, I had no idea I had OM's. As a migraine sufferer, I'm accustomed to headache pain...this phenomenom, however, involved no pain whatsoever! What drove me to seek medical attention was that while I'd be asleep, shocking spurts of bright white light would explode behind my closed eyelids, startle the crap out of me & wake me up from a dead sleep. I don't like anything messing w/my sleeptime, so I made an appt. to see the doctor. Anyway, he diagnosed ocular migraines. He also said that since they're usually not accompanied by pain, there's really no medical treatment prescribed. He told me to ignore them, that the episodes would pass (they did) & be glad that they weren't a typical head-splitting, debilitating migraine headache! He said causes for them are the same as for regular migraine -- certain foods, alcohol, hormone fluctuations, etc. Does that help?