Closing your eyes often results in the perception of light, color, or patterns, even when external light is completely blocked. This demonstrates that seeing is not solely dependent on light entering the eye, but is also a function of the visual system’s internal activity. The neural pathways for sight can be activated spontaneously or by non-light stimuli, generating internal images interpreted by the brain as visual input. These normal perceptions originate from various points along the visual pathway, from the retina to the visual cortex.
Phosphenes: Visualizing Internal Electrical Activity
Phosphenes are the most common internal visual sensation, appearing as flashes, sparks, dots, or simple geometric patterns seen when the eyes are closed. These perceptions arise from the physical or electrical stimulation of the retina or optic nerve, rather than actual light photons. The visual system interprets any signal received from the optic nerve as light, regardless of its origin.
A frequent cause is mechanical stimulation, such as gently pressing on the closed eyelid. This pressure deforms photoreceptors and retinal ganglion cells, triggering an electrical impulse the brain registers as a burst of light, often called “seeing stars.” Phosphenes also occur spontaneously during rapid eye movements (saccades) in the dark, where mechanical tension on the retina initiates a brief visual signal.
Phosphenes can also be induced by external electrical or magnetic stimulation, as the current directly excites neurons in the visual pathway. Additionally, spontaneous firing of cells in the visual system—neural “noise”—can exceed a threshold and be consciously perceived. These simple light perceptions are a default function of a constantly active visual pathway.
Hypnagogia: Complex Imagery in the Sleep Transition
When simple phosphenes transition into complex, detailed, or narrative visual experiences, the phenomenon is often hypnagogia, related to falling asleep. This state is characterized by vivid, dream-like imagery, yet the individual often maintains some awareness. Hypnopompic imagery is the corresponding phenomenon experienced upon waking, when the brain is caught between sleeping and waking states.
The visual content is often elaborate, featuring clear images of faces, landscapes, moving figures, or complex, colored patterns. These images are typically transient, appearing and disappearing quickly as a single scene rather than a continuous plot. These visual sensations frequently involve other sensory experiences, such as hearing strange noises or voices, or feeling physical sensations like floating or a hypnic jerk.
Hypnagogic experiences are a normal manifestation of consciousness shifting from the wakeful state to sleep. This state involves a mix of brainwave patterns, including pre-sleep alpha waves and an intrusion of REM-like activity. The brain attempts to reconcile waning external sensory input with an active, dream-generating internal system, producing these complex visualizations.
Retinal Afterimages
Afterimages are visual phenomena that occur immediately following the removal of a strong external visual stimulus. The brain continues to perceive the image that was just viewed, a persistence of vision resulting from photoreceptors temporarily adapting to intense light exposure.
There are two main types: positive and negative. A positive afterimage appears in the same colors as the original object and is usually very brief, lasting less than a second. This is caused by photoreceptor cells continuing to fire neural impulses after the light source is removed, reflecting persistent activity in the visual system.
A negative afterimage is more common and lasts longer, displaying the complementary colors of the original image. For example, staring at a bright red object results in a cyan afterimage. This color inversion is a sign of retinal fatigue, where the cone cells detecting the original color become temporarily desensitized, allowing opponent-color cells to dominate the visual signal.
When Internal Images Signal a Health Concern
While most internal visual experiences are benign, certain characteristics of these phenomena may indicate an underlying health issue and warrant medical evaluation. A sudden, dramatic increase in flashes or the appearance of new, numerous floaters can be a warning sign of a serious ocular condition. These symptoms may signal a posterior vitreous detachment or, more concerningly, a retinal tear or detachment. In these cases, the vitreous gel pulls away and mechanically stimulates the retina, causing the perception of light.
Flickering, expanding arcs of light or geometric patterns that appear in both eyes, often lasting between 5 and 60 minutes, may be a visual aura preceding a migraine headache. This is a neurological event involving a wave of altered electrical activity that spreads across the visual cortex.
If the visual phenomena are complex, recurrent hallucinations—such as seeing detailed figures, faces, or scenes—and occur while a person is fully awake but has significant vision loss, it may be a sign of Charles Bonnet syndrome (CBS). CBS is a condition where the brain generates vivid images to compensate for the loss of sensory input, often seen in individuals with age-related macular degeneration or glaucoma. People with CBS maintain insight, meaning they know the images are not real, and the hallucinations are not a sign of a psychiatric disorder. Any sudden change in the frequency, complexity, or nature of internal visual phenomena should be assessed by a healthcare professional to rule out potentially sight-threatening or neurological conditions.