Does it look a bit like this?
https://en.wikipedia.org/wiki/Scinti...ng_scotoma.gif
Then see the following:
https://en.wikipedia.org/wiki/Scintillating_scotoma
You can get these with or without migraine.
I had one a few days ago after eating a few chocolates following a couple of weeks without any. The effect lasts for me between 5 mins and a couple of hours.