When you close your eyes, do you ever see shifting colors, patterns, or flashes of light? This common experience sparks curiosity, as these internal light shows appear even in complete darkness. This article explores the science behind these intriguing visual sensations, explaining why our brains create light when no external light is present.
What Are Phosphenes?
The scientific term for these internally generated visual sensations is phosphenes, derived from the Greek words “phos” (light) and “phainein” (to show). Phosphenes appear as flashes of light, swirls of color, geometric patterns, or even temporary dots and squiggles. They can appear as glittery sparkles or stars. These visual experiences are not perceptions of external light, but rather the brain’s interpretation of signals originating from within the visual system itself.
The Science Behind These Visual Experiences
Our visual system does not simply shut off when external light is removed; it remains active even with closed eyes. This internal activity can produce various types of phosphenes through different mechanisms. One common cause is mechanical stimulation, such as gently rubbing your eyelids or experiencing sudden pressure on the eye. This physical pressure directly stimulates the light-sensitive cells in the retina, sending signals to the brain that are then interpreted as light, even though no actual light entered the eye.
Other everyday actions like coughing, sneezing, or even a blow to the head can also induce phosphenes, often described as “seeing stars.” This mechanical stimulation leads to a temporary perception of light, as retinal cells are excited and trigger nerve impulses the brain processes visually.
Even in complete darkness, the visual system exhibits a baseline neural activity that can create faint, shifting patterns or “visual noise.” This phenomenon is sometimes referred to as darkness phosphenes or entoptic phenomena, which are visual effects originating within the eye itself. Some theories suggest that our retinal cells may even produce their own minute amounts of light, known as biophotons, which the brain interprets as visual signals in the absence of external light.
When to Consult a Doctor
While occasional phosphenes caused by pressure or seen in darkness are generally harmless, certain visual symptoms warrant medical attention. A sudden onset of persistent flashes of light, especially if accompanied by new floaters, which are small specks or squiggly lines drifting in your vision, can be a sign of a serious underlying issue. These symptoms might indicate a retinal tear or detachment, where the retina pulls away from its supportive tissue. A “curtain-like shadow” coming across your vision is another urgent warning sign.
Phosphenes that occur frequently, are intensely bright, or are associated with other neurological symptoms also require evaluation. For instance, shimmering zigzag lines, often expanding gradually, or blind spots, can be symptoms of a migraine aura, which may or may not be followed by a headache. If these visual disturbances are accompanied by severe headaches, dizziness, speech difficulties, numbness, or muscle weakness, consulting a healthcare provider is important. Any significant change in the nature, frequency, or intensity of phosphenes that causes concern or interferes with daily life should prompt a visit to an eye care professional for proper diagnosis and care.