Sounds like Ocular Migraines. I've gotten them now for about 10 years. Usually I get them in clusters after not having them for a few months.
Wish I knew if it were something more controllable.
For me it's a bright, shimmering little thing that grows over my entire vision over 30-45 minutes. When it finally subsides, I get a pretty awful headache for 1-2 hours. Ibuprofen fortunately does help with the headache, at least.