A phosphene is the phenomenon of seeing light without light entering the eye. Phosphenes can be induced by mechanical, electrical, or magnetic stimulation of the retina or visual cortex, or by random firing of cells in the visual system. Phosphenes that are induced by movement or sound may be associated with optic neuritis. Phosphenes have also been reported by meditators, people who endure long periods without visual stimulation, or those who ingest psychedelic drugs.