When you close your eyes, you might occasionally notice unexpected flashes or streaks of light. This common phenomenon can be a puzzling experience, sometimes even causing a moment of alarm. While seeing these internal lights can be a sign of a serious underlying eye condition, it is often a harmless occurrence. Understanding the various reasons behind these perceptions can help differentiate between a normal bodily function and a symptom requiring medical attention.
What Are Eye Flashes?
Eye flashes, scientifically termed photopsias, are the perception of light originating within the eye or brain, not from an external source. These perceived lights can appear as shimmering spots, streaks, zigzags, or bright bursts. The retina, a light-sensitive tissue at the back of the eye, translates light into electrical signals for the brain. When retinal cells or the optic nerve are stimulated, the brain interprets these signals as light, even without actual light present.
Common Benign Explanations
One frequent and harmless reason for seeing flashes when closing your eyes involves pressure phosphenes. These occur when mechanical pressure directly stimulates the photoreceptors in the retina. For example, gently rubbing your closed eyelids or pressing firmly on your eye can deform the retinal cells, causing them to send electrical signals that the brain interprets as transient patterns or fields of light.
Another common explanation relates to dark adaptation and spontaneous retinal noise. In low-light conditions or complete darkness, the retina’s sensitivity increases as it adjusts to detect faint light. During this process, photoreceptor cells can spontaneously generate low-level electrical signals, even without external light input. The brain may occasionally perceive these random firings as faint, fleeting flashes or shimmering patterns.
Minor movements within the vitreous gel, the clear, jelly-like substance filling the eyeball, can also cause subtle flashes. The vitreous is attached to the retina at various points. As the eye moves or the vitreous naturally shifts, it can tug slightly on the retina. These gentle pulls can stimulate the retinal cells, resulting in a momentary perception of light.
Concerning Medical Explanations
While many eye flashes are harmless, some can indicate more serious medical conditions. Posterior Vitreous Detachment (PVD) is a common age-related condition where the vitreous gel shrinks and pulls away from the retina. As the gel detaches, it can tug on the retina, causing flashes often described as lightning streaks or sudden bursts, particularly noticeable in peripheral vision. While PVD is usually benign, this pulling can sometimes lead to complications.
A more urgent concern arises if the vitreous gel’s pulling creates a retinal tear or detachment. If the vitreous gel pulls hard enough, it can tear the delicate retinal tissue. Fluid can then pass through the tear and accumulate behind the retina, causing it to detach. Flashes associated with a retinal tear or detachment are sudden in onset, persistent, and often accompanied by a significant increase in new floaters or a dark shadow or “curtain” encroaching on vision.
Flashes can also be a component of a migraine aura. These flashes are distinct, often appearing as geometric patterns, shimmering zigzags, or expanding blind spots that last for 20 to 30 minutes. Unlike flashes originating from the retina, migraine auras are neurological events caused by abnormal electrical activity in the brain’s visual cortex. They typically affect both eyes and resolve as the headache begins or progresses.
When to Seek Medical Attention
You should seek immediate attention from an eye care professional if you experience a sudden onset of new flashes, or a noticeable increase in their frequency or intensity. This change could signal a developing issue within the eye.
Flashes accompanied by a sudden increase in new floaters are a significant warning sign. Any perception of a dark curtain or shadow moving across your visual field, or a loss of peripheral vision, also requires urgent assessment. If flashes occur after a head or eye injury, or if you experience any persistent flashes without a clear, benign explanation, prompt consultation is advised. Timely assessment is crucial to prevent vision loss from serious eye conditions.