Closing your eyes often brings a kaleidoscope of colors, patterns, or flashes of light. Far from being unusual, these internal light shows are a normal function of our visual system, illustrating how the brain processes signals even in the absence of external light.
Understanding Phosphenes
The primary scientific explanation for seeing visuals with closed eyes centers on phosphenes. These are visual sensations of light that occur without light entering the eye, originating from within the visual system itself.
The underlying mechanism involves stimulating various parts of the visual pathway, including the retina, optic nerve, and visual cortex. Even when your eyes are closed, retinal cells can spontaneously fire electrical signals. The brain interprets these internal electrical impulses as light or visual patterns, much like it interprets signals from external light sources.
This internal generation of visual signals explains why you can “see” light or patterns in complete darkness. The visual system does not simply switch off when deprived of external light; instead, it continues to generate a form of “visual noise” that the brain translates into phosphenes. The term “phosphene” comes from Greek words meaning “light” and “to show,” aptly describing this self-generated light show.
Common Causes and Appearance
Phosphenes can be triggered by a variety of common actions and conditions. One frequent cause is physical pressure on the eyes, such as gently rubbing your closed eyelids. This mechanical stimulation activates light-sensitive cells in the retina, sending signals to the brain perceived as light.
Other common triggers include sudden changes in the body or environment. Many people experience phosphenes, often described as “seeing stars,” after a vigorous sneeze, a heavy cough, or a sudden change in blood pressure like standing up too quickly. Rapid transitions from bright to dark environments can also induce these visual effects as the retina adapts. In prolonged darkness, some individuals may experience a continuous, low-level visual noise, sometimes referred to as “prisoner’s cinema.”
The appearance of phosphenes often includes swirling colors, geometric patterns, flashes, dots, squiggles, or shimmering lights. These patterns can be quite intricate, with some descriptions including bright circles or a scintillating light grid. The specific form and color of a phosphene can depend on the nature of the stimulus and where in the visual system it originates.
Beyond Phosphenes: Other Closed-Eye Experiences
While phosphenes account for many common closed-eye visuals, other, more complex phenomena can occur, particularly during transitions between wakefulness and sleep. These are distinct from phosphenes, as they involve higher brain functions and are more akin to dream-like states.
One such phenomenon is hypnagogic imagery, which refers to vivid visual, auditory, or tactile experiences that happen as you are falling asleep. Similarly, hypnopompic imagery occurs during the process of waking up. These experiences can be quite elaborate, featuring detailed scenes, figures, or even sounds, unlike the simpler patterns of phosphenes.
These sleep-wake transition hallucinations are thought to involve parts of the brain that are partially awake while others are still in a sleep state. Factors such as stress, fatigue, or certain medications can sometimes influence the frequency and intensity of these more complex visuals. Unlike phosphenes, which are a direct sensory response to internal stimulation, hypnagogic and hypnopompic visuals are often considered a normal part of the brain’s transition between conscious states.
When to Be Concerned
Most experiences of seeing things with closed eyes are normal and do not indicate a medical problem. However, specific instances could signal an underlying issue that warrants medical attention.
You should consult an eye care professional if the flashes of light are persistent, occur suddenly, or significantly increase in frequency or intensity. Be particularly attentive if these flashes are accompanied by a sudden increase in “floaters” (small specks or squiggly lines that drift across your vision), a dark curtain-like shadow over your field of vision, or any reduction in overall vision. These symptoms could indicate a serious condition such as a retinal tear or retinal detachment, which requires prompt evaluation to prevent permanent vision loss.