I have visual disturbance in both eyes that are circles like octaagons (refracted light best describes them) basically in the shape of a c and starts small and becoms quite large until it no longer fits in my visual field. I can cover one eye up and I see it in the other eye and vice versa which indicates to me it's not in any one eye specifically. It lasts approx 20 minutes each time. How do I find out what this might be. I've had my vision checked and it's fine. I have no headaches, and through process of elimination, I can associate nothing with it. This has gone on for several years and occurs very sparatically. I do wear reading glasses.