Seeing flashes of light in your vision, medically termed photopsia, can be a startling experience. These visual disturbances appear as quick sparks, streaks of lightning, or shimmering lights that seem to come from inside the eye. While many instances are harmless, the presence of new or sudden flashes always warrants a professional eye examination. Understanding the characteristics of the flashes is the first step in determining the underlying cause and the urgency of seeking care.
Temporary Visual Disturbances
Flashes appearing in both eyes simultaneously and moving across the visual field are typically not related to the eye’s physical structure. The most common source of these bilateral, temporary flashes is a migraine aura, sometimes called an ocular migraine. This phenomenon is a neurological event caused by a wave of electrical activity across the brain’s visual cortex.
A migraine aura often manifests as a shimmering, expanding area of zigzag lines or a fort-like pattern. This disturbance gradually moves from the center of vision toward the periphery, usually lasting 10 to 30 minutes before resolving. The visual episode may occur with a subsequent headache, or it can happen without head pain, a condition known as acephalgic migraine.
Another recurrent, non-ocular cause is Visual Snow Syndrome. This syndrome is characterized by the persistent perception of tiny, static-like dots or flickering lights across the entire visual field.
Vitreous Changes and Flashes
The majority of flashes occurring in only one eye result from mechanical stimulation of the retina, the light-sensitive tissue lining the back of the eye. The eye’s central cavity is filled with the vitreous humor, a clear, gel-like substance attached to the retina. As a person ages, the vitreous naturally begins to liquefy and shrink, causing it to pull away from the retina.
This separation is known as a Posterior Vitreous Detachment (PVD). It is a common, age-related event affecting about 75% of people over the age of 65. When the shrinking gel tugs on the retina, the retinal cells are mechanically stimulated, sending an electrical signal to the brain interpreted as a flash of light. These flashes are described as brief streaks or sparks, often appearing in the peripheral vision. PVD is also typically accompanied by the sudden onset of new floaters, which are shadows cast by the condensing vitreous gel.
Signs of Retinal Damage
While PVD is a natural aging process, strong pulling by the vitreous can lead to serious complications. If the vitreous gel is abnormally adherent, the separation can exert enough force to tear the underlying retinal tissue. A retinal tear is a medical emergency because it allows fluid from the vitreous cavity to accumulate behind the retina, causing it to peel away from its supportive layers.
The symptoms signaling a retinal tear or detachment are distinct and urgent. These events are usually marked by a sudden increase in both the number and intensity of flashes and floaters. The most concerning sign is the appearance of a gray, dark, or smoky curtain or shadow that starts in the peripheral vision and progressively moves inward. This visual field defect is the physical manifestation of the detached retina losing its function, often followed by a painless loss of vision.
When to Seek Emergency Care
Any new or sudden onset of flashes requires prompt evaluation by an eye care professional, such as an ophthalmologist. Though the cause may be the common PVD, only a dilated eye examination can reliably rule out a sight-threatening retinal tear or detachment. Early intervention is important because a small tear can be sealed with a quick in-office laser procedure or freezing treatment, preventing a full detachment.
You should seek emergency care immediately if the flashes are accompanied by a sudden shower of new floaters, a shadow or curtain blocking any part of your vision, or any vision loss. A retinal detachment is a time-sensitive condition, and every hour matters for preserving vision. Delaying treatment significantly increases the risk of permanent vision impairment.