Many people occasionally experience flashing lights when their eyes are closed, a phenomenon that can range from common and harmless to a sign of an underlying medical condition. These visual sensations, known as phosphenes, are perceptions of light without actual light entering the eye. Understanding the different causes of these flashes can help distinguish between a normal occurrence and something that warrants medical attention.
The Science Behind Normal Flashes
A common and harmless reason for seeing flashes of light with closed eyes involves how the eye’s light-sensing cells are stimulated internally. One type is pressure phosphenes, which occur when mechanical pressure is applied to the eyeball. For example, rubbing your eyes can stimulate retinal cells, leading to the perception of colors or stars. The retina, the light-sensitive tissue at the back of the eye, interprets this stimulation as light.
Normal flashes can also occur during dark adaptation, as the visual system adjusts to low-light conditions. After bright light exposure, eye sensitivity increases in darkness. During this process, spontaneous neural activity within the visual system may be perceived as fleeting lights or patterns. This adjustment involves the regeneration of photopigments in the photoreceptor cells. These flashes are brief and do not indicate a problem.
When Flashes Signal Something Else
While many flashes are harmless, some signal underlying medical conditions. Issues with the retina, the thin layer of nerve tissue lining the back of the eye, are a common cause for concern. As people age, the vitreous humor, a clear, jelly-like substance, can shrink and pull away from the retina in a process called posterior vitreous detachment (PVD). This pulling can cause flashes, often described as lightning streaks or sparks, particularly noticeable in peripheral vision or dim lighting. While PVD is a natural part of aging and often harmless, it can sometimes lead to more serious conditions like a retinal tear or detachment.
Retinal tears or detachment occur when the retina pulls away from its normal position, potentially leading to vision loss if not treated promptly. Flashes associated with these conditions are sudden, intense, and may appear as streaks of lightning or stars. These flashes may be accompanied by a sudden increase in floaters, which are small specks or cobweb-like shapes drifting in the field of vision. Ocular migraines, also known as migraine aura without headache, are another cause of visual flashes. These neurological events cause visual disturbances like shimmering lights, zigzag patterns, or blind spots, typically affecting both eyes, lasting 5 to 60 minutes, often without a headache.
When to Seek Medical Advice
It is important to recognize when flashing lights indicate a need for medical evaluation. A sudden onset of new flashes, especially if persistent or increasing in frequency and intensity, warrants immediate consultation with an eye care professional. This is particularly true if flashes are accompanied by a sudden shower of new floaters. These combined symptoms could signal a retinal tear or detachment, which are medical emergencies.
Other red flags include a “curtain” or “veil” obscuring part of vision, a sudden decrease in vision, or flashes following head trauma. These symptoms may suggest a serious issue requiring urgent attention to prevent permanent vision loss. Consult an ophthalmologist or seek emergency medical care if any concerning symptoms appear, as timely diagnosis and treatment can significantly impact the outcome.