I've written before about one of my symptoms, which seems to be quite rare, I can have a absence brought on by a number of things including sound and vision. First thing to say despite people raising epilepsy it's not but due to my right frontal lobe injury.
I don't know what the particular test is called but it's testing peripheral vision, you press a button when you see something appear in your field of view. I'd warned the optician as previously it'd been a problem. "Different test not a flashing light", "It's not photosensitive epilepsy but let give it a try".
I had to stop after 30 seconds as I could feel a absence coming on.
Anything like that out there?