Naked Science Forum

Non Life Sciences => Geek Speak => Topic started by: Lewis Thomson on 17/01/2022 10:08:02

Title: Why do we see phosphenes?
Post by: Lewis Thomson on 17/01/2022 10:08:02

Sacha and Xenia have sent in this peculiar question.

"My daughter and I were having fun pressing our eyes and getting some crazy patterns. We looked up them and found that they are called phosphenes. What struck us particularly was that some patterns are perfectly geometrical - like a chess board. We were blown away that our bodies could produce something so mechanical looking - maybe, we wondered, are we actually robots but don't know it?"

What do you think? Leave your comments down below...

Title: Re: Why do we see phosphenes?
Post by: Origin on 17/01/2022 13:23:19

I think you should stop pressing on your eyeballs.

Title: Re: Why do we see phosphenes?
Post by: chiralSPO on 17/01/2022 16:13:17

We are "wet" robots.

I agree with Origin, it's probably best not to press on your eyes (though I suspect that phosphenes become visible before any irreversible damage can be done).

My understanding is that phosphenes can be caused by lack of oxygen to the eyes. For example, they can be visible when you have a major drop in blood pressure to the head (I have postural hypotension, and sometimes see them if I stand up very quickly after lying flat for a long time). Slight pressure applied to the eyes may also serve the purpose of cutting off circulation (slightly). At rest, your eyes use the most oxygen of ay part of your body (by mass), and a lot of this has to do with keeping the nerves working correctly.

As far as the geometrical patterns go: It is known that eyes gather far more information per second than could possibly be transmitted through the optic nerve, so there is a lot of "pre-processing" or signal compression. An image is transformed from a vast array of "pixels" into a collection of shapes and colors (this is how many optical illusions work—they don't trick the brain, they trick the eye itself!). My hypothesis for the highly geometrical patterns is this: when deprived of oxygen, some of the nerves misfire (either at the pixel level, or the processing—I don't know), but somehow the signals going through the optic nerve are artifacts in the form of lines and shapes and colors.