The experience of seeing a circle, flash, or burst of light when you blink, close your eyes, or apply gentle pressure is a common visual phenomenon. This sensation of light is generated entirely within your visual system, independent of any external light source. It is an internal visual artifact that many people encounter, often without realizing there is a scientific explanation for the event. Understanding this internal mechanism helps explain why a simple action like blinking can sometimes create a brief, luminous shape in your field of view.
Understanding Phosphenes: The Brain’s Perception of Pressure
The scientific term for seeing light when no light is present is phosphene, derived from the Greek words for “light” and “to show.” Phosphenes demonstrate that the sensory cells of the eye can be activated by non-light stimuli, essentially tricking the brain into perceiving illumination. The retina contains specialized photoreceptor cells that typically respond to photons, but these cells are also mechanosensitive, meaning they can be stimulated by mechanical force.
When any signal is sent from the retina through the optic nerve to the visual cortex, the brain’s default interpretation is that the signal represents light. Applying pressure to the eyeball triggers this visual sensation because the mechanical deformation of the eye’s globe physically stresses the retinal cells. This causes them to fire an electrical impulse as if they had been struck by light, which the brain processes as a visual image.
The circular or arc-like shape often reported is a direct result of the spherical structure of the eye and how pressure distributes across the retina. When you press on the side of your closed eyelid, the pressure deforms the ocular globe. This mechanical stimulation creates a ring or arc of light in the visual field opposite the location of the pressure, a well-documented form of pressure phosphene.
Common Benign Causes of Circular Visual Artifacts
The brief, non-threatening visual artifacts seen when you blink or move your eyes are typically pressure phosphenes caused by minor, everyday forces. Simply blinking forcefully can cause a quick, momentary increase in pressure on the ocular surface. This slight compression is usually enough to stimulate a small area of the retina, resulting in a brief flash or circle of light that quickly dissipates.
Rapid eye movements, especially during deep sleep or when shifting focus quickly, can also generate these flashes. The muscles moving the eye place subtle traction on the retina, which is enough to mechanically activate the photoreceptors and produce an arc or circle of light. This effect is often more noticeable in dark environments because the visual system is more sensitive to minimal stimulation.
Another common benign cause is the presence of “floaters,” which are shadows cast onto the retina by tiny collagen fibers or cellular debris suspended within the vitreous humor. While floaters are typically described as specks or cobwebs, the separation of the vitreous gel from the retina can sometimes result in a large, circular floater known as a Weiss ring. This specific circular shape represents the former attachment site of the vitreous to the optic nerve head and is usually a sign of a normal aging process.
When the Circle Signals a Serious Problem
While most flashes and circles are harmless, persistent or sudden changes in these visual artifacts can signal an underlying condition that requires immediate medical evaluation. The most concerning characteristic is the sudden onset of a shower of new floaters, often described as a cloud of “gnats” or “pepper,” accompanied by an increased frequency and intensity of flashes. These symptoms suggest that the vitreous gel, the clear substance filling the eye, is pulling too strongly on the retina.
This traction is a primary feature of a Posterior Vitreous Detachment (PVD), a common age-related process where the vitreous separates from the retina. Although PVD is generally benign, the pulling action can sometimes cause a retinal tear. A retinal tear is indicated by flashes that are not just fleeting circles but persistent, bright streaks of light, especially in the peripheral vision.
A Retinal Detachment is a medical emergency where the retina peels away from its underlying supportive tissue. This condition often manifests as a shadow, curtain, or veil moving across the field of vision.
Flashes or circles that appear as geometric, shimmering, or zigzag patterns and last for several minutes are often associated with an ocular migraine, also known as a migraine aura. These visual disturbances are typically painless and originate from electrical activity in the visual cortex of the brain.
Flashes induced by eye or head movement, particularly when accompanied by blurred vision or pain, may be a symptom of optic neuritis, which involves inflammation of the optic nerve. Any sudden, dramatic change in the appearance, frequency, or duration of flashes or the sudden appearance of a dark shadow warrants an urgent consultation with an eye care professional.