Entoptic Forms

Incidentally, you can also see phosphenes without hallucinogenic substances by pressing on your closed eyes (with your thumbs or knuckles). You can then see beautiful, changing patterns because nerve cells in your eyes are activated under pressure. Do be careful, however, because if you do this for too long, too often, or too hard, you could damage the inside of your own eyeball!

These visual forms are generated by mechanical deformation of your eyes, not by light. (Deformation of nerves can lead to action potentials in nerve pathways.) Such patterns are recognized in the underlying brain regions through visual memory. In this way, you can perceive repetitive, slowly changing geometric shapes. Such phosphenes are also called ‘entoptic forms’, that is to say: moving, figurative forms within the optical perception system of the eye.

Animation: Artificial imitation of an entoptic form in the visual system of the brain.