[dracon (OP)]

Conrad Berube asked the Naked Scientists:
   
Dear Chris:

Greetings from British Columbia where I have taken time off from leaping from tree to tree as they float down our mighty rivers-- with my best girl by my side-- to ask the following medical question (which suggests a theme for whole show, that is, the question does, not the leaping bit):  every once in a while I will wake up - I think it's usually when I've been lying on my back - and as I look around the room I seem to see a red disk that seems to float around the dark room as I look around tracking wherever my gaze wanders.  (I figure that it probably is some kind of phosphene caused by blood pooling in the macula of the retina or something similar.)  Is this a common enough phenomenon to have a known cause or should I get checked for brain tumors?

I believe it would be a really interesting to dedicate a whole show to cover these kinds of neurological illusions like some of those I found at newbielink:http://www.telegraph.co.uk/technology/3350191/The-upside-down-world-of-illusions.html [nonactive] when I searched for that term on Google, things like the "gorilla in our midst", the Pinocchio illusion, the phantom third arm, the McGurk Effect etc.

Conrad Berube

What do you think?

[RD]

should I get checked for brain tumors?

You should see an eye doctor (optometrist /ophthalmologist), who can examine your retina, (the only pain this examination causes is in the wallet). You shouldn’t drive for a few hours afterwards until the medication which causes pupil dilation has worn off, (maybe take sunglasses to wear during this period).

If your symptom was say an early stage of conditions like retinal detachment or glaucoma they are treatable if caught early.

I believe it would be a really interesting to dedicate a whole show to cover these kinds of neurological illusions like some of those I found at http://www.telegraph.co.uk/technology/3350191/The-upside-down-world-of-illusions.html

The "UPSIDE-DOWN FACE", a.k.a. "Thatcher effect" has already been covered ...

http://www.thenakedscientists.com/HTML/content/news/news/1743/

http://www.thenakedscientists.com/forum/index.php?topic=20060.msg225562#msg225562

[dracon (OP)]

Actually I just had an eye examination a month ago-- there were no indications of glaucoma, macular degeneration, retinal detachment, etc.  The phantom floating red "spotlight" effect is a regular, though infrequent, nocturnal occurrence-- it is more puzzling to me than worrisome.

[RD]

The phantom floating red "spotlight" effect is a regular, though infrequent, nocturnal occurrence

So you only "see" it in darkness ? ...

The Prisoner's Cinema is a phenomenon reported by prisoners confined to dark cells and by others kept in darkness, voluntarily or not, for long periods of time. It has also been reported by truck drivers, pilots, and practitioners of intense meditation ...

The "cinema" consists of a "light show" of various colors that appear out of the darkness. The light has a form, but those that have seen it find it difficult to describe.

http://en.wikipedia.org/wiki/Prisoner%27s_cinema

when you've half-asleep ? ... http://en.wikipedia.org/wiki/Hypnagogia#Sights