White flashes of light seen in the corner of the eye, medically known as photopsia, can be a startling experience. These flashes often appear as lightning streaks or camera flashes, particularly noticeable in low-light conditions. While common, this visual disturbance always warrants a professional medical assessment to determine its source. The causes range from temporary neurological events to structural changes within the eye, making assessment important for preserving vision.
The Biological Mechanism of Visual Flashes
Photopsia occurs when the retina, the light-sensitive tissue at the back of the eye, is stimulated without actual light entering the eye. The retina converts light into electrical signals that the brain interprets as images. When this tissue is mechanically agitated, it fires electrical impulses, which the brain mistakenly perceives as a flash of light.
This mechanical stimulation most often involves the vitreous gel, a clear, jelly-like substance that fills the center of the eyeball and is normally attached to the retina. If the vitreous pulls or tugs on the retina, the retinal cells are forced to fire. This causes the sensation of a flash or streak of light, which is typically brief and appears in the peripheral vision.
Common, Non-Urgent Causes of Flashes
Some flashes originate within the brain’s visual processing centers rather than the eye itself and are generally harmless. Ocular migraines, also known as visual or silent migraines, are a common non-urgent cause of photopsia. These episodes result from temporary changes in blood flow or electrical activity in the visual cortex, not physical traction on the retina.
Migraine-related flashes often present as shimmering, zigzag lines, or geometric patterns that slowly expand across the field of vision, termed scintillating scotoma. Unlike mechanically induced flashes, these disturbances usually last for several minutes (10 to 20 minutes) and may or may not be followed by a headache. Brief flashes can also be triggered by non-disease events, such as rubbing the eyes hard or experiencing a sudden drop in blood pressure. This abrupt change physically stimulates the retina, causing a fleeting visual spark known as a phosphene.
Urgent Causes Requiring Immediate Attention
The most significant cause of photopsia relates to age-related changes in the vitreous. As a person ages, the vitreous gel naturally liquefies and shrinks, a process known as Posterior Vitreous Detachment (PVD). PVD is common in people over 65, and usually, the vitreous cleanly pulls away from the retina without issue.
However, if the vitreous is strongly attached, the pulling creates mechanical stress on the retina. Forceful tugging can tear the retinal tissue, resulting in a Retinal Tear. Flashes in this context are often sudden, persistent, and localized to the periphery, signaling ongoing mechanical traction.
A retinal tear is serious because fluid can pass through the opening and accumulate behind the retina, pushing it away from its underlying blood supply. This separation of tissue from its nourishment is known as Retinal Detachment, a medical emergency that can lead to permanent vision loss if not repaired promptly. Flashes signaling a detachment are typically bright streaks of lightning and are often accompanied by a sudden increase in floaters.
Accompanying Warning Signs and Medical Evaluation
Flashes are a symptom, and the presence of other accompanying signs often signals an emergency. Any sudden increase in floaters—small spots, threads, or cobwebs drifting across the vision—should be considered an urgent warning sign. A more alarming symptom is the perception of a dark shadow, curtain, or veil moving across the field of vision, which suggests a retinal detachment is underway.
A professional medical evaluation is the only way to accurately determine the cause of photopsia and rule out a serious condition. The primary diagnostic tool is a dilated eye exam, where drops widen the pupil, allowing the doctor to view the entire retina. The ophthalmologist inspects for signs of a retinal tear, detachment, or other structural abnormalities. If a retinal tear is found, early treatment with a laser or freezing procedure can often seal the tear and prevent a full retinal detachment.