I suffer from attacks during which I see brightly colored jagged
circles, sometimes in one eye, sometimes in both.  They begin as very
small circles, but then, constantly moving, they expand into large
circles.  These episodes last between 15 to 20 minutes. They became
very frequent, until I began taking Plavix which seems to have almost
entirely stopped them. I would like to know if anyone else has
experienced similar symptoms and/or if anyone knows the cause.

tal3100...

I'll be interested to hear any responses, as I have experienced
something similar. My experience has been limited to only my left
eye, and the experience starts more as a line or a small oval, as
I remember it (it hasn't happened for a long time).

It would then expand, as you've noted, and, for me, the visual
expanded into a display of moving light that can only be described
as psychedelic in color and texture, with the light moving in some
relatively consistent manner, and the patterns being somewhat jagged
in nature.

As in your case, this display would persist for 10-20 minutes and
then gradually fade. It would be visible with eyes open or closed,
and superimpose itself on the visual field if the eyes were open.

In my experience, it was often associated with stressful situations
such as working outside in Arizona summer heat, or, at times, inside,
in a high-stress situation. For this reason, I considered that the
phenomenon might have some relationship to an increase in blood
pressure, but this is mere conjecture, since I made no attempt to
gather data which would support this supposition.

It is interesting to note, however, that, since adopting a less
stressful lifestyle for the past few years, the condition has not
recurred.

sublime1-ga

Sounds like something I have experienced.  My eye doctor thought it
was a normal  - maybe slightly abnormal -  reaction to a bright light,
similar to the complementary color effect.  That seemed possible, as
it only occurred a couple of times when I was reading and may well
have glanced up at a bright window.
It hasn't happened in years.