Experiencing flashes of light when your eyes are closed is a common visual phenomenon. These internal perceptions, known as phosphenes, are often described as seeing stars, sparks, or streaks of light and are typically harmless.
Understanding Phosphenes
Phosphenes are perceptions of light that occur without light actually entering the eye. The term “phosphene” originates from Greek words meaning “light” and “to show.” These visual sensations arise from the stimulation of the retina, the optic nerve, or the visual cortex in the brain. The retina, a layer of nerve tissue at the back of the eye, converts light into electrical signals sent to the brain.
When the cells in the visual system are stimulated by something other than external light, the brain interprets these signals as flashes or patterns of light. This can happen through mechanical, electrical, or even magnetic stimulation. The visual cortex interprets these generated signals as light, even in complete darkness.
Common Triggers and Normal Experiences
Many everyday actions can induce phosphenes, which are considered harmless. One of the most frequent causes is applying pressure to the eyelids by rubbing your eyes. This mechanical stimulation directly activates the photoreceptor cells in the retina, leading to light and color perceptions.
Other common triggers include sudden head movements or standing up too quickly, which can cause a temporary drop in blood pressure. Forceful actions like sneezing or coughing can also increase pressure around the eyes, resulting in brief flashes. Pressure on the optic nerve from certain body positions can stimulate these light perceptions. Brief flashes experienced in total darkness or upon waking are also normal, as the visual system can spontaneously fire.
When Flashes Signal a Concern
While many instances of seeing flashes are benign, these sensations can sometimes indicate a more serious underlying eye condition. Recognizing the difference is important for eye health.
A sudden onset of new flashes, especially when accompanied by new floaters (specks, lines, or cobweb-like shapes), can be a warning sign of a retinal tear or detachment. Retinal detachment occurs when the retina pulls away from its supporting tissue, which can lead to permanent vision loss if not treated quickly. Symptoms may include a shadow or “curtain” appearing across the field of vision.
Posterior vitreous detachment (PVD) is another common, age-related condition where the gel-like vitreous in the eye separates from the retina. This pulling action can cause flashes of light, often described as brief streaks in peripheral vision, and an increase in floaters. While PVD itself is not sight-threatening, it can sometimes lead to a retinal tear, requiring an eye examination.
Flashes can also be a symptom of an ocular migraine or migraine with aura. These visual disturbances may appear as geometric patterns, zigzag lines, shimmering lights, or blind spots, and can occur with or without a headache. Migraine auras typically affect both eyes, while retinal migraines, a rarer condition, cause visual symptoms in only one eye, such as temporary vision loss or twinkling lights. Other less common causes of flashes include optic neuritis, where the optic nerve becomes inflamed, or certain brain-related issues. Any sudden increase in the frequency or intensity of flashes, or flashes accompanied by other visual changes like new floaters or vision loss, warrants an immediate eye examination.