The experience of closing your eyes only to be met with swirling colors, shimmering patterns, or brief flashes of light is a common event. These internally generated visuals can appear as geometric shapes, diffuse patches of color, or a static-like field of dots. Though it may seem counterintuitive to see light when all external sources are blocked, this phenomenon is a normal byproduct of your visual system’s continuous activity. This appearance of inner lights demonstrates how the eye and brain work together, proving that visual perception is a dynamic process.
The Science Behind Phosphenes
The scientific term for these internally generated light sensations is phosphenes, which are visual percepts that occur without actual light entering the eye. Phosphenes arise because the cells responsible for vision can be activated by stimuli other than photons, the particles of light. The visual system, which includes the retina and the visual cortex in the brain’s occipital lobe, is highly sensitive and is programmed to interpret any strong signal from the retina as light.
The retina contains photoreceptor cells and neurons that convert light into electrical signals sent to the brain. When these cells are mechanically or electrically stimulated, they fire impulses that are indistinguishable from those produced by external light. The brain’s visual cortex receives this signal and, unable to determine the signal’s origin, translates it into the perception of color and light. This mechanism is responsible for the diverse array of shapes, from bright circles and shimmering grids to diffuse, colored patches.
The resulting patterns are a manifestation of the visual pathway’s spontaneous activity being triggered by non-light events. Researchers have found that stimulating the visual cortex directly with electrical current can produce phosphenes, demonstrating that the perception of light is ultimately generated deep within the brain. This shows that the visual experience is an artifact of the central nervous system’s activity, which is always ready to process any incoming signal as a visual event.
Common Physical Triggers of Internal Light
Mechanical pressure is one of the most common ways to trigger this phenomenon, resulting in pressure phosphenes. Rubbing your closed eyelids physically deforms the eyeball, which directly stimulates the photoreceptor cells in the retina. This mechanical stimulation causes the cells to fire a burst of electrical energy that the brain instantly translates into a burst of light and color, leading to the sensation of “seeing stars.”
Another frequent cause of phosphenes is darkness adaptation, often referred to as the “prisoner’s cinema.” When the eyes are closed in a dark environment, the photoreceptor cells, particularly the rods, become highly sensitive in an effort to detect any available light. This increased sensitivity leads to the spontaneous, low-level firing of retinal cells and visual neurons. The result is a slow, shifting display of faint colors, complex patterns, and visual noise.
Phosphenes can also be generated by rapid eye movements, known as saccades. As the eyes move, the tugging of the muscles and the resulting slight mechanical stress on the retina and optic nerve can cause a brief, transient flash of light. This temporary stimulation is enough to generate a quick visual spark that fades almost immediately after the eye movement stops.
When to Seek Medical Advice
While the colors and flashes you see when closing your eyes are harmless phosphenes, sudden or persistent visual disturbances can signal an underlying medical issue. Normal phosphenes are transient and only occur upon mechanical pressure or in complete darkness with closed eyes. The concerning symptoms, by contrast, typically occur suddenly and persist while the eyes are fully open.
A sudden onset of persistent flashes of light, especially in the peripheral vision, could be a sign of a posterior vitreous detachment. This condition occurs when the vitreous gel inside the eye shrinks and pulls away from the retina, a common event of aging. However, if the pulling is too strong, it can tear the retina.
A retinal tear or detachment is a medical emergency, indicated by a sudden, dramatic increase in flashes and floaters, along with a dark, curtain-like shadow moving across the field of vision. If you experience these symptoms spontaneously, consult an eye care professional immediately.