The experience of seeing lights flicker or flash when no external light source is present is a common visual symptom. This phenomenon is a signal originating from within your visual processing system, not a problem with the environment. The brain interprets signals from the eye as light, even if generated by mechanical or neurological irritation instead of actual photons. These visual disturbances require professional evaluation to determine the underlying cause.
Defining the Visual Anomaly
The medical term for perceiving light when there is no objective light source is photopsia. These visual anomalies are subjective, ranging widely in description. People may report seeing brief, lightning-like streaks, camera-flash pops, shimmering heat waves, or expanding zigzag patterns. These flashes are generally described as “positive” photopsia, involving the perception of light or shapes.
Photopsias differ from the dark specks known as “floaters,” though they often occur together. The sensation of light is created when the retina, the light-sensitive tissue at the back of the eye, is stimulated by something other than light. This contrasts with a negative visual anomaly, such as a blind spot (scotoma), where a portion of vision is temporarily lost. The specific appearance and timing of these flashes provide ophthalmologists with clues about their origin.
Causes Originating in the Eye Structure
The most frequent cause of new-onset photopsia relates to changes in the eye’s structure, specifically the interaction between the vitreous humor and the retina. The vitreous is a clear, gel-like substance that fills the eyeball and is normally attached to the retina. As a person ages, this gel naturally liquefies and shrinks, a process known as syneresis.
This age-related change eventually causes the vitreous to pull away from the back of the eye, a condition called Posterior Vitreous Detachment (PVD). As the vitreous separates, it can tug on the delicate retina, which is lined with photoreceptor cells.
This mechanical traction stimulates the photoreceptors, causing them to fire an electrical signal that the brain interprets as a sudden flash or streak of light, often described as a curved line in the peripheral vision. PVD is common and typically benign, and the flashes usually diminish as the vitreous fully separates from the retina over a few weeks or months.
However, if the vitreous gel is strongly adhered to the retina, the pulling can cause a retinal tear. This is a serious condition where flashes are often more intense, sudden, and resemble a bright camera flash or lightning strike. Fluid from the vitreous cavity can then pass through the tear, lifting the retina from its underlying tissue, leading to a sight-threatening retinal detachment. Less common ocular causes for photopsia include inflammation (uveitis) or certain complications from diabetes affecting retinal blood vessels.
Causes Originating in the Brain and Body
Flickering and flashing lights can also originate from the brain’s visual processing center, the visual cortex. The most recognized neurological cause is the visual aura associated with a migraine. This disturbance, known as a scintillating scotoma, typically begins as a small, shimmering spot near the center of vision and gradually expands into a geometric pattern of zigzag lines.
The pattern often takes the shape of a C-arc, caused by a slow wave of electrical activity (cortical spreading depression) moving across the visual cortex. Unlike retinal flashes, this flickering affects both eyes simultaneously. It can occur even without a subsequent headache, a phenomenon termed a silent migraine. These events typically last between five and sixty minutes before resolving.
Another systemic cause relates to the body’s cardiovascular regulation, such as orthostatic hypotension (a sudden drop in blood pressure upon standing). Moving quickly from a sitting or lying position causes blood to momentarily pool in the lower extremities, reducing blood flow to the brain and retina. This temporary reduction in oxygenated blood supply can cause a brief, generalized flickering, dimming, or “graying out” of vision that quickly resolves once blood flow is restored.
Sudden visual disturbances, particularly if accompanied by other neurological symptoms, can warn of a Transient Ischemic Attack (TIA), or mini-stroke. A TIA involves temporary blockage of blood flow to the brain or eye. Certain medications, including some high-dose antibiotics or blood pressure drugs, can also induce temporary photopsia as a side effect.
Identifying Red Flag Symptoms
While many instances of photopsia are benign, certain associated symptoms indicate a medical emergency requiring immediate attention from an eye specialist. The most urgent red flag is the sudden onset of a shower of new flashes, especially if accompanied by a significant increase in floaters. This combination suggests a high risk of a retinal tear or detachment.
The appearance of a dark shadow, curtain, or veil that obstructs any part of the visual field is a hallmark symptom of a progressing retinal detachment and demands the fastest possible medical intervention. Flashes that occur alongside systemic symptoms—such as sudden weakness on one side, difficulty speaking, confusion, or a severe, abrupt headache—should prompt an immediate emergency room visit. These neurological symptoms suggest a possible TIA or stroke, where rapid treatment is paramount to prevent permanent damage. Any new or persistent visual flickering should be evaluated.