There are several of us on here who have a similar eye complaint: seeing a bright flash, like the afterimage of a flash bulb, when we blink, and sometimes, on upgaze. This is
transient symptom for
most of us, lasting anywhere from a few days
to a few weeks. When the "spot" in our vis
ual field passes over a dark background, the spot appears light. When the spot passes over a light background, it appears dark.