Sounds like migraine.
Mine start as a small blob of light in one eye, then grows into a coloured zig zag, which is curved round, and gets larger until it disappears out of the edge of my vision.
It's usually followed by a headache, but not a particularly bad one - I get off quite lightly compared to some people.
If I catch it early enough and concentrate on watching the blob (with my eyes shut), it will sometimes disappear and not develop into the zig zag or the headache.