When eyes close, the visual experience extends beyond simple darkness. Many report seeing various patterns, colors, or complex imagery. Understanding this phenomenon involves examining the eye’s physiological mechanics and the brain’s visual system.
The Basic State: Darkness
When the eyes are closed, the primary perception is darkness because eyelids block external light from reaching the retina. The retina, at the back of the eye, contains photoreceptors that require light stimulation to send visual signals to the brain.
However, this “darkness” is not always absolute black. Even in a completely dark environment with closed eyes, many perceive a subtle, grainy, or fluctuating gray, sometimes called “eigengrau” or “brain gray.” This suggests the visual system maintains a baseline activity level, even without external light.
Unpacking Phosphenes: Lights Without Light
A common experience when eyes are closed is perceiving light without an external source, known as phosphenes. These internal visual sensations can manifest as flashes, sparkles, dots, squiggles, swirls, or geometric patterns of various colors. The term “phosphene” comes from Greek words meaning “light” and “to show,” aptly describing these internally generated lights.
Phosphenes often occur due to mechanical stimulation of the retina or optic nerve. Gently rubbing closed eyes, for example, applies pressure that stimulates photoreceptor cells, causing these lights, often described as “seeing stars.” Actions like sneezing, coughing, or a sudden blow to the head can also induce phosphenes by increasing eye pressure or mechanically stimulating the visual system. They can also arise from spontaneous electrical activity within retinal cells or the brain’s visual system. While typically harmless, persistent phosphenes may indicate underlying medical conditions, such as retinal issues, optic nerve inflammation, or certain neurological conditions like migraines.
The Brain’s Contribution: From Patterns to Visions
Even with eyes closed, the brain’s visual system remains active and can generate complex visual experiences. The visual cortex, responsible for processing visual information, does not require direct eye input to create perceptions. Instead, it produces its own imagery based on neural activity. This internal generation of visuals ranges from intricate patterns to vivid, dream-like scenes.
As a person transitions into sleep, they may experience hypnagogic imagery, including swirling colors, random pixels, or clear images of people, objects, and places. These experiences occur in the hypnagogic state, the transitional period between wakefulness and sleep. During this state, the brain disengages from external stimuli and becomes more receptive to internal signals. The visual cortex, particularly the secondary visual cortex, interprets this internal data, creating “visions” from neural noise or memory fragments. This demonstrates the brain’s capacity to construct visual realities even without external light.