Many people experience seeing colors, patterns, or flashes of light even with their eyes closed. This common visual phenomenon often appears as swirling shapes, dots, or transient streaks of color. It is a normal part of how our visual system functions, even in the absence of external light.
The Phenomenon of Phosphenes
These perceived colors and patterns seen without external light are scientifically known as phosphenes. The term “phosphene” originates from Greek words meaning “light” and “to show,” aptly describing these light sensations that are not caused by actual light entering the eye. Phosphenes can appear as swirling colors, small dots, fleeting flashes, or intricate geometric shapes. They are transient, harmless, and considered a normal aspect of visual perception. The experience can be compared to the visual system continuing to operate, much like a camera that is still recording even with its lens cap on.
The Science Behind the Colors
The appearance of phosphenes involves several physiological mechanisms within the visual system. One common trigger is mechanical stimulation, such as rubbing your eyes. When pressure is applied to the eyeball, it directly stimulates the photoreceptor cells in the retina, which are the light-sensing cells at the back of the eye. This mechanical activation causes these cells to send electrical signals to the brain, which then interprets them as flashes or patterns of light, often described as “seeing stars” after a sneeze, cough, or mild head impact.
Even in complete darkness, the retina and optic nerve maintain a low level of background electrical activity. These spontaneous electrical signals are interpreted by the brain as light, contributing to the faint, shifting colors one might see with closed eyes. Our eyes are not designed to distinguish between light from the outside world and this self-generated light, so the optic nerve transmits these internal signals to the brain for interpretation.
The brain’s visual processing centers, particularly the visual cortex, can also generate these sensations even without direct input from the eyes. This activity can be influenced by various internal states. For example, phosphenes can occur in conditions like migraines, appearing as flickering zig-zag lines or shimmering lights. In some instances, specialized techniques such as transcranial magnetic stimulation can directly activate parts of the visual cortex, producing vivid phosphenes.
Normal Versus Concerning Visions
Most instances of seeing colors or patterns with closed eyes are benign phosphenes and do not indicate a health concern. However, certain visual phenomena are distinct and warrant medical attention, as they may indicate underlying eye conditions.
Specific “red flag” symptoms suggest a more serious issue that requires prompt evaluation by an eye care professional. These include the sudden appearance of persistent flashes of light, particularly in the peripheral vision, which may resemble lightning streaks. Another concerning sign is a sudden increase in the number of floaters, which are small specks, dots, or squiggly lines that drift across the field of vision. A shadow or “curtain” obscuring part of the vision is also a significant warning sign. These symptoms could indicate serious conditions such as retinal detachment or vitreous detachment, which require timely intervention to preserve vision.