Phosphene

Formation_of_phosphenes

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Phosphene is a phenomenon characterized by the experience of seeing light without light actually entering the eye. This can occur spontaneously or be caused by external stimuli such as pressure on the eye or electricity. Phosphenes are most commonly introduced by simply closing the eyes and rubbing them or squeezing them shut, tightly.

Causes

Phosphenes can be directly induced by mechanical, electrical, or magnetic stimulation of the retina or visual cortex, or by random firing of cells in the visual system. They have also been reported by meditators (commonly called nimitta), people who go for long periods without visual stimulation (also known as the prisoner's cinema), or those who are using psychedelic drugs.

Mechanism

The most common phosphenes are pressure phosphenes, caused by rubbing the closed eyes. They have been known since antiquity, and described by the Greeks. The pressure mechanically stimulates the cells of the retina. Experiences include a darkening of the visual field that moves against the rubbing, a diffuse colored patch that also moves against the rubbing, a scintillating and ever-changing and deforming light grid with occasional dark spots (like a crumpling fly-spotted flyscreen), and a sparse field of intense blue points of light. Pressure phosphenes can persist briefly after the rubbing stops and the eyes are opened, allowing the phosphenes to be seen on the visual scene.

See also

• Entoptic phenomenon
• Closed-eye hallucination
• Visual snow
• Hallucination
• Haidinger's brush
• Aura (symptom)