Closing your eyes often leads to perceiving flashes of light, colors, or intricate patterns, especially in complete darkness. This common phenomenon, where unbidden lights and shapes appear even without external light, is a normal part of how our visual system functions. This article explores the scientific explanation behind these intriguing visual sensations.
Understanding Phosphenes
The scientific term for seeing light sensations without actual light entering the eye is “phosphenes.” These visual perceptions originate from within the visual system, rather than from external light stimuli. Phosphenes are a form of photopsia, which broadly refers to flashes of light.
One primary physiological cause of phosphenes is mechanical stimulation. Applying pressure to the eyeball, such as by gently rubbing your closed eyes, can directly stimulate the photoreceptor cells in the retina. This mechanical pressure causes these light-sensitive cells to fire electrical signals, which the brain interprets as light, leading to the perception of colors or patterns.
Another reason phosphenes appear is due to spontaneous neural activity within the visual system. Even in absolute darkness, the retina, optic nerve, and visual cortex of the brain are not entirely dormant. They can exhibit low-level, random electrical discharges. The brain processes these spontaneous signals as visual input, resulting in the perception of light or shapes where none exists externally.
Less common factors can also induce phosphenes, including certain chemical or electrical stimulations. Some medications, for instance, can cause these visual phenomena as a side effect. Intense or changing magnetic fields, such as those used in transcranial magnetic stimulation (TMS), can directly activate cells in the visual cortex or retina, leading to magnetophosphenes. Radiation exposure, like during radiation therapy, can also excite retinal cells and produce light flashes.
How Phosphenes Appear
Phosphenes can manifest in various visual forms, often described as sparks, squiggles, swirling patterns, or patches of color. They might also appear as geometric shapes or a general visual “static” or “noise.” The colors observed can differ, commonly including blues, greens, and yellows, though other hues are possible.
These internal light shows are most frequently observed in specific contexts. The most common scenario is in complete darkness or when the eyes are closed. In the absence of external light, the brain may attempt to “find” visual input, making the spontaneous activity within the visual system more noticeable.
Physical pressure on the eyes is another frequent trigger. Rubbing the eyes or pressing against them often results in immediate phosphene displays. Sudden increases in head pressure, such as those from sneezing, coughing forcefully, or even quick movements, can also briefly induce phosphenes.
While phosphenes are generally normal and harmless, their appearance can occasionally be associated with certain medical conditions. For example, they might occur as part of a migraine aura. Intense or persistent phosphenes can also indicate underlying retinal issues, such as posterior vitreous detachment, retinal detachment, or blood pressure changes. If these visual sensations become frequent, intense, or are accompanied by other visual disturbances, consulting a healthcare professional is advisable for evaluation.