Perceiving flickering lights or patterns even when your eyes are closed, especially in a dark environment, is a common experience. This phenomenon, often described as seeing “stars” or shimmering shapes, is widespread and typically harmless. These internal light shows can range from subtle glows to vivid, intricate patterns.
Understanding Phosphenes
The internal lights seen with closed eyes are known as phosphenes. The term “phosphene” originates from Greek words meaning “light” and “to show,” aptly describing the sensation of light without an external light source. Phosphenes are not actual light entering the eye, but rather the brain’s interpretation of signals generated within the visual system itself. These visual perceptions can arise from various forms of stimulation to the retina or the visual cortex in the brain.
The eye and brain are capable of generating these visual perceptions internally due to the inherent activity of photoreceptors in the retina. Even in the absence of light, these specialized cells can spontaneously generate neural signals. When these signals reach the brain, it processes them as if actual light were present, resulting in the experience of phosphenes.
Common Explanations for Flickering Lights
Most instances of flickering lights or patterns seen with closed eyes are benign and result from common, non-concerning causes. One frequent explanation involves “pressure phosphenes,” which occur when mechanical pressure is applied to the eyeball. Rubbing your eyes, pressing on your eyelids, or even rapid eye movements during sleep can stimulate the retina and optic nerve, leading to these visual sensations. The pressure activates retinal cells in a manner similar to light, causing the brain to interpret the signals as visual phenomena.
Another common cause is related to dark adaptation and retinal noise. In prolonged darkness, the retina’s light-sensitive cells can spontaneously generate low-level neural signals. This “noise” in the visual system can be perceived as faint, flickering lights or patterns as your eyes adjust to the absence of external light. This is a normal physiological process, reflecting the continuous activity within the visual pathway.
Additionally, “entoptic phenomena” can contribute to these internal visuals. These are visual effects whose source is within the eye itself, such as blood vessels or vitreous floaters. While floaters typically appear as specks or threads, the movement of the vitreous gel within the eye can sometimes cause flashes of light, especially as it pulls on the retina. These often become more noticeable in low light or when looking at a plain background.
When Flickering Lights Signal a Deeper Concern
While many instances of flickering lights are harmless, certain characteristics can indicate a more serious underlying medical condition. Visual disturbances that appear suddenly, persist, or are accompanied by other symptoms should be evaluated by a healthcare professional.
One concern is an ocular migraine or migraine aura. These are neurological events that can cause visual disturbances, such as shimmering, flickering, or zigzagging patterns, often referred to as scintillating scotomas. These visual effects can occur in one or both eyes and may precede or accompany a migraine headache. The patterns typically expand across the visual field and can last anywhere from a few minutes to an hour.
Flashes of light, sometimes described as “lightning streaks” or bright spots, can also be symptoms of retinal issues. These may signal a posterior vitreous detachment (PVD), where the vitreous gel separates from the retina, or a retinal detachment. In PVD, the flashes often occur in the peripheral vision and may be accompanied by new floaters. A retinal detachment is a medical emergency where the retina pulls away from its supporting tissue, potentially leading to permanent vision loss if not treated quickly. Sudden increases in flashes and floaters, or a shadow in your vision, warrant immediate medical evaluation.
Other neurological or systemic conditions can also manifest with visual symptoms. These include optic neuritis, involving inflammation of the optic nerve, or certain cerebrovascular events. If flickering lights are accompanied by symptoms like weakness, dizziness, speech problems, or severe headaches, or if they are new and persistent, consult a healthcare professional.