Phosphenes

Phosphenes are the perception of light without light entering the eye. They occur when the visual system is activated by stimuli that do not originate from external photons, typically through stimulation of the retina or the visual cortex.

Retinal phosphenes arise from direct stimulation of retinal tissue. They can be produced by mechanical means, such as rubbing or applying pressure to the eye, or by electrical stimulation from retinal implants or transcorneal devices. Cortical phosphenes result from stimulation of the visual cortex, often via methods such as transcranial magnetic stimulation or direct electrical stimulation during neurosurgical procedures. The subjective experience of phosphenes varies widely, with reports of colored spots, flashes, lines, or geometric shapes that may appear in the field of view and can last from milliseconds to several seconds or longer.

Phosphenes occur in both healthy individuals and patients with certain conditions. They can be induced experimentally for research purposes, contribute to clinical clues in neurology and ophthalmology, and play a role in emerging visual prosthetics that aim to convey visual information to blind or severely visually impaired users through patterned phosphene perceptions.

Etymology and history: the term phosphene comes from Greek roots meaning light and to show, and the phenomenon has been described in various forms since antiquity, with modern usage formalized in the 19th century.

See also: scintillations, migraine aura, visual prosthetics, transcranial magnetic stimulation.