I went in for an optometrist visit a few months ago for an eye exam looking
for any information on some flashes I was having (which have subsided for
the most part) and strange wobbling of vision/disequilibrium sensation that
I've been getting for weeks at a time on and off.  It's just a brief rocking
motion or sense of imbalance but only lasts a second or two, no spinning
sensation, I have no ataxia, can walk straight lines, do the usual balance
tests as well as I've ever been able to.  I'll have weeks where it's
happening, and then weeks where it's all but gone.  Before the exam he was
looking at me and mumbled that I had "naturally large pupils".  We were
already sitting in a dim room, and I didn't think much of it, I've never
noticed that or been told that before.

Then several weeks ago while looking in the mirror in the bathroom I had
looked at my eyes, looked up to style my hair a bit (leaned over toward the
mirror at the same distance the entire time), and when I looked back down
several seconds later I noticed that both of my pupils were very large.
I've since noticed this a lot in the bathroom mirror, one moment my pupils
will look normal, I'll look around the mirror or around the bathroom, look
back and my pupils are huge.  They respond to light - if I tilt my head back
they immediately constrict, and I spoke with the optometrist who last
examined me who confirmed that they reacted normally with no obvious defect
(he tested one pupil's response to light in the other, and then in it).
They just seem to get huge while I'm in there, and I assume at other times
too if others have noticed.

I tested the light and found that there are six 40 watt bulbs in the
bathroom arrayed across the top of the mirror.  I tried putting in one 150
watt bulb and turning the rest off, and I'm not able to get the pupils to
constrict as much, there is definitely quite a bit more brightness than the
six 40 watt bulbs.  But, still, the light with the 40 watt bulbs is
sufficient to shave, read directions on products, etc., it's just softer and
not 'bright white'.

I've also tested my eyes with a small key light, shining it directly into
the eyes.  The pupils immediately constrict, though once constricted they
seem to dilate just a bit and then re-constrict randomly, though they're
always much smaller than without the light in them.

Am I worried for nothing here?  I've been worried on a daily basis about the
previously mentioned stuff, have been to a doctor, had a few blood tests (I
have not had a thyroid test yet) that all came back "perfectly normal",
etc., but I haven't been pulling my hair out or biting my nails, just a bit
stressed from it all.  Someone said it could "just be stress", but if that's
the case why would it only happen in slightly low light rather than
elsewhere?  My obvious worry after having the optometrist exam (I have
myopia, described as 'legally blind' for driving but am correctable to 20/20
with glasses, but physically my eyes and nerves looked perfect) is something
like a brain tumor, especially with the brain fog I've had for several
months.  I have no swelling in the back of the eye, no glaucoma, I don't
have headaches or nausea.