Seeing patterns, flashes, or circles of light when your eyes are closed or in complete darkness is a common biological phenomenon. This visual display is a normal function of the visual system operating without external light stimulation. The appearance of these inner lights is tied directly to the electrical activity within your eyes and brain, a process that continues regardless of external viewing conditions.
Phosphenes: The Light You See in Darkness
The visual sensations you perceive without light entering the eye are scientifically termed phosphenes, derived from the Greek meaning “light appearance.” Phosphenes are the visual system’s way of generating a signal internally, and the brain interprets this signal as light, even when no external light source exists. They can manifest in various forms, including diffuse colored patches, bright circles, or scintillating grids. These sensations are categorized into two main groups: spontaneous, occurring in total darkness, and induced, requiring some form of non-light stimulation.
The Retina’s Built-In Electrical Activity
The source of spontaneous phosphenes lies in the constant, low-level electrical activity of the retina, the light-sensitive tissue at the back of the eye. Specialized cells, known as photoreceptors, convert light into electrical signals that the brain can understand. These cells are never truly “off,” and they continue to fire signals even in the absence of light. The two types of photoreceptors, rods and cones, constantly generate a small amount of “dark noise” or random electrical impulses. The brain processes this random electrical background noise as faint, moving shapes or a grainy visual static, which is why you see subtle, shifting patterns in the dark.
How Physical Pressure Affects Phosphenes
The most noticeable and intense phosphenes, often described as bright, complex circles or “seeing stars,” are caused by physical stimulation. These are known as pressure phosphenes or mechanical phosphenes, resulting from external force applied to the eye. Actions like rubbing your eyes, pressing on the eyelids, or a sudden change in blood pressure physically deform the retina’s tissue. This mechanical force directly stimulates the photoreceptor cells, causing them to fire much more intensely and in a coordinated burst compared to their spontaneous activity. The visual system cannot distinguish between the mechanical stimulation of the retina and the stimulation caused by actual photons of light, so the signal sent to the brain is interpreted as a powerful flash or complex, bright shapes.