When flashes of light suddenly appear in your vision, the experience can be startling. This phenomenon, medically termed photopsia, involves seeing brief bursts or streaks of light not caused by external sources. These visual disturbances originate from within the eye or the brain, typically due to stimulation of the retina. The retina is the light-sensitive tissue lining the back of the eye that converts light into electrical signals. When the retina is physically stimulated, it fires these impulses, causing the perception of light flashes.
Vitreous Changes
The most frequent cause for flashes is the age-related transformation of the eye’s internal structure. The eye’s largest chamber is filled with the vitreous humor, a clear, jelly-like substance attached to the retina. As a person ages, the vitreous naturally begins to liquefy and shrink, causing it to separate from the retina. This event is known as a Posterior Vitreous Detachment (PVD) and affects nearly 75% of people by age 65.
During this separation, the shrinking gel can tug on the sensitive retina, which the brain interprets as a flash of light. These photopsias are often described as lightning streaks or camera flashes. They are typically seen in the peripheral vision and may be more noticeable in dark environments or when the head moves. Once the vitreous gel fully separates, the mechanical stimulation stops, and the flashes usually subside over weeks or months.
Retinal Tears and Detachment
Although PVD is a natural aging process, it can sometimes lead to more serious complications. If the vitreous gel is strongly adhered, it may pull with enough force to create a tear in the retina during separation. A retinal tear is an urgent situation because fluid can pass through the tear and collect underneath the retina. This fluid accumulation lifts the retina away from the underlying blood vessel layer, resulting in a retinal detachment.
Retinal detachment is a sight-threatening emergency requiring prompt surgical intervention to prevent permanent vision loss. Flashes associated with a tear may be more persistent and intense than those caused by a simple PVD. These flashes may also be accompanied by a sudden shower of new floaters, which are shadows cast by debris entering the vitreous. A distinguishing symptom of a progressing detachment is the appearance of a dark shadow or gray curtain moving across the field of vision.
Causes Originating Outside the Eye
Flashes of light do not always indicate a problem within the eye; they can sometimes be a sign of neurological events. The most common non-retinal cause is a migraine with aura, sometimes called an ocular migraine. The visual symptoms are caused by abnormal electrical activity spreading across the visual cortex in the brain, not by mechanical tugging on the retina. These flashes are typically characterized by shimmering, zigzag lines, or geometric patterns that affect vision in both eyes simultaneously.
Migraine aura usually lasts between 5 and 60 minutes and often resolves completely before a headache begins, or sometimes occurs without a headache. The appearance of these lights is distinctly different from the brief, peripheral streaks associated with retinal issues. Other non-eye-related causes of photopsia include transient ischemic attacks or changes in blood pressure, which temporarily disrupt blood flow to the visual pathways.
Immediate Warning Signs
Because the eye cannot distinguish between a harmless PVD and a sight-threatening retinal tear, any new onset of flashes requires a prompt examination by an eye care professional. You should seek emergency medical care immediately if you experience a sudden increase in the number or intensity of light flashes.
Urgent Symptoms
A sudden, significant increase in floaters, sometimes described as a shower of black specks, is an urgent warning sign. The most alarming symptom is the sensation of a gray or dark curtain moving across the visual field, which signals a retinal detachment. Vision loss or a narrowing of peripheral vision accompanying the flashes also necessitates an emergency evaluation.