Flashes of light, medically termed photopsia, are visual sensations that occur without any external light source. These sensations originate within the eye or the brain, signaling a disturbance in the visual system. Since the retina translates light into images, any physical stimulation of this structure can trick the brain into perceiving illumination. Photopsia can represent anything from a common age-related change to a serious medical emergency.
Describing the Visual Experience
The appearance of photopsia is highly variable, but it is often described in specific ways. Many people report seeing flashes that resemble streaks of lightning or quick, curved arcs, particularly in the peripheral vision. These flashes are typically fleeting, lasting for only a fraction of a second. The color is most commonly perceived as white or clear, though some individuals may report silvery or slightly colored sparks.
The flashes may also take the form of quick sparks, pinpricks, or flickering lights, often more noticeable in dim lighting conditions or when moving the head or eyes. A different pattern of photopsia involves shimmering, wavy lines or zigzagging shapes that can resemble heat rising from asphalt. This latter type of visual disturbance is usually longer-lasting than the quick, peripheral flashes.
The Physical Cause of Seeing Light
The fundamental cause of photopsia originating in the eye involves the interaction between the vitreous humor and the retina. The vitreous humor is the clear, gel-like substance that fills the large central cavity of the eyeball, and it is adhered to the retina, the light-sensitive tissue lining the back of the eye.
As a person ages, the vitreous gel naturally begins to shrink and liquefy, causing it to pull away from the retina. This pulling action, known as traction, physically stimulates the delicate retinal tissue. Since the retina’s only function is to send signals interpreted as light to the brain, this mechanical stimulation causes the retinal cells to fire, resulting in the perception of a flash.
Immediate Warning Signs
While many flashes are benign, certain characteristics indicate a serious condition, such as a retinal tear or detachment. Flashes associated with these issues are often described as sudden, intense, and occurring frequently. They may be accompanied by a sudden increase in floaters, which can appear as a “shower” of black spots, specks, or cobwebs.
A sign of particular concern is the perception of a dark shadow, gray curtain, or veil moving across the field of vision, which suggests the retina is pulling away from the underlying tissue. Retinal detachment is a medical emergency because the detached tissue is cut off from its blood supply, risking permanent vision loss. Immediate consultation with an eye doctor or emergency room visit is necessary if these sudden, severe symptoms occur, as prompt treatment can help protect vision.
Other Common Triggers
Flashes can also be caused by less urgent conditions. The most frequent cause of flashes is Posterior Vitreous Detachment (PVD), which is the normal, age-related separation of the vitreous gel from the retina. The flashes from an uncomplicated PVD are typically quick, peripheral, and often resolve themselves as the vitreous completely separates. This is a common and expected change in the eye, though it still requires examination to ensure no tear has occurred.
Another common source of flashes is a migraine with visual aura. These flashes are distinct because they usually affect both eyes and are characterized by geometric patterns, such as shimmering, zigzagging lines that slowly expand across the vision. The visual disturbance from a migraine aura generally lasts between 10 to 30 minutes, and may or may not be followed by a headache.