Many people experience seeing light or visual patterns with closed eyes. This common phenomenon ranges from simple perceptions to complex experiences, stemming from eye and brain activity. Understanding these mechanisms helps explain these internal light shows.
Physical and Retinal Origins
Phosphenes are common internal light perceptions, appearing as flashes or patterns without actual light entering the eye. They often occur when mechanical pressure, like rubbing closed eyelids, directly stimulates retinal cells. Actions such as sneezing, intense coughing, or a blow to the head can also induce phosphenes, often described as “seeing stars.”
Beyond external pressure, the visual system generates Eigengrau, or “intrinsic gray.” This uniform dark gray is seen in the absence of visible light, even with eyes closed in darkness. Eigengrau is not true black; it results from continuous, spontaneous activity within retinal photoreceptor cells and brain’s visual pathways. This “visual noise” means the visual system is never entirely inactive, constantly sending signals the brain interprets as this intrinsic gray.
Brain-Generated Visuals
Visual perceptions with closed eyes can originate from brain activity, not just retinal stimulation. Hypnagogic hallucinations are one example, occurring during the transition to sleep. They manifest as changing geometric patterns, shapes, light flashes, or even formed images. While vivid, these hallucinations are typically brief and not concerning, with many people experiencing them.
Migraine auras are another brain-generated visual phenomenon. These sensory disturbances can precede or accompany a migraine, often lasting less than an hour. Visual auras may include flashing lights, colored spots, shimmering zigzag lines, or temporary blind spots. These symptoms arise from an electrical or chemical wave moving across the brain’s visual processing areas.
Beyond the Benign
While many instances of seeing light with closed eyes are harmless, certain characteristics might signal a serious medical condition. Sudden, new flashes of light, especially if persistent or accompanied by other visual disturbances, warrant immediate medical attention. These could indicate issues with the retina.
A sudden increase in “floaters”—small specks or dark spots that drift across vision—especially when combined with flashes of light, can be a warning sign. This may indicate a posterior vitreous detachment (PVD), where the vitreous gel separates from the retina.
While PVD is often age-related and harmless, it can sometimes lead to a retinal tear or detachment. Retinal detachment is a medical emergency that can cause permanent vision loss if untreated.
Other concerning symptoms include a shadow or “curtain” over part of the vision, or sudden vision loss. Neurological conditions, such as stroke or brain tumors, can also cause visual disturbances like flashes of light, blurred vision, or sudden vision changes, making professional evaluation important.
Understanding the Differences
Distinguishing between benign visual phenomena and those requiring medical attention involves several factors. The light’s nature is important: are they brief, isolated flashes, or persistent patterns like shimmering zigzag lines? Flashes that appear suddenly, repeatedly, or are new should prompt concern.
The presence of accompanying symptoms is a significant differentiator. If flashes combine with a sudden increase in floaters, especially new or numerous ones, or if there is any loss of peripheral vision or a shadow obscuring vision, seek prompt medical evaluation.
While isolated phosphenes and Eigengrau are harmless, any visual disturbances that are new, worsening, or significantly impact daily life warrant discussion with an eye care professional to rule out serious underlying conditions.