Optimum:
The first time it happened, I was driving along when it slowly dawned on me that all the other cars on the road only had three wheels. The shimmering rainbow had cut out a chunk of my vision but my brain did its best patch up what I was seeing. I was told it was caused by chocolate or red wine. I tried a massive claret and stilton OD with no effect. I now think the attacks are triggered by bright, low level sunlight reflection off car windows, or by stress. I can carry on working through the attack which last about 20 minutes but it leaves me feeling rough. Its best to park up, lie down in the dark and wait until the rainbow has completed its circumnavigation of my field of vision I sometimes feel strangely elated after an attack.
I think that’s called “Azul” or “Azur” - where your brain makes up visual data for your visual cortex, because your eyes are literally deceiving you.
I have a nasty feeling it is a DVLA-notifyable thing that’ll lose you you licence, if there are repeated attacks, or simply no regained vision after such an “attack”. 
Stress and Tiredness - must aggravate these conditions as well of course, not to mention ‘age’.