Asked by: Emma Smith, Peterhead
These shapes and colours, called ‘phosphenes’, were reported as long ago as the time of the ancient Greeks. Rubbing your eyes increases the pressure within the eyeball and this pressure activates ganglion cells in the retina in the same way as light does. Your brain doesn’t know the difference and so interprets the activation as though you were seeing light from the world outside.
Most common phosphenes are diffuse blobs of different colours that move with the rubbing. Then there are scintillating and rapidly moving grid-like patterns which probably reflect the organisation of cells higher up in the visual system. These patterns are reminiscent of psychedelic paintings because the major hallucinogens also affect the visual system.
Other effects include an array of intense blue points of light. If you want to experience these, be careful and press gently for some time rather than pressing too hard and risking damage to the eye.