Seeing a flash, streak, or arc of light in your peripheral vision can be a startling experience. Medically, this sensation is known as photopsia, which is the perception of light when no external light source is present. This phenomenon occurs because of the mechanical or electrical stimulation of the retina, the light-sensitive tissue at the back of the eye, or the visual processing centers in the brain. While flashes can be a common and harmless event, they may also signal a serious, vision-threatening condition, making a professional eye examination necessary to determine the cause.
Transient and Non-Structural Causes
Not every visual flash indicates a structural problem with the eye; some are temporary and benign, originating outside the retina. A common non-structural cause is the visual aura associated with a migraine, sometimes called an ocular or acephalgic migraine. These involve shimmering, zigzagging patterns or bright spots that usually affect both eyes and last between five minutes and one hour, often occurring without a subsequent headache.
Another frequent, transient cause is orthostatic hypotension, a momentary drop in blood pressure when a person stands up too quickly. This sudden reduction in blood flow can briefly deprive the retina and visual cortex of adequate oxygen, causing the perception of “seeing stars” or temporary dimming of vision. Simple mechanical pressure, such as rubbing the eye firmly, can also excite the photoreceptor cells, leading to the perception of light known as phosphenes. These instances are usually brief, resolve quickly, and do not cause lasting damage.
The Role of the Vitreous Gel
The most frequent structural cause of photopsia is related to the vitreous humor, the clear, gel-like substance filling the center of the eyeball. The vitreous is attached to the retina, particularly at the back of the eye. As a person ages, the vitreous gel naturally undergoes a process called syneresis, where it liquefies and shrinks, becoming more watery over time.
This liquefaction eventually causes the vitreous to separate from the retina, an age-related occurrence known as Posterior Vitreous Detachment (PVD). As the shrinking gel pulls away, it can tug on attached regions of the retina. The retina interprets this mechanical stimulation as light, which the patient perceives as a brief flash, streak, or camera-flash effect, often seen in the peripheral vision. PVD is generally benign, affecting the majority of people over 80, but the acute onset of flashes and floaters still warrants an examination to rule out complications. The flashes associated with an uncomplicated PVD are typically short-lived and decrease in frequency as the separation completes.
Urgent Indicators of Retinal Damage
While an uncomplicated PVD is harmless, the traction on the retina can sometimes be strong enough to cause a tear, requiring immediate attention. If a tear occurs, fluid can pass through the opening and separate the retina entirely, leading to a retinal detachment.
The key indicators that a flash may signal a more urgent issue are the sudden onset of new, persistent flashes or a simultaneous shower of new floaters. Floaters in this context are often caused by blood or pigment cells released into the vitreous from the torn retinal tissue. The perception of a shadow or a dark curtain progressing across the field of vision is a classic symptom indicating a developing retinal detachment. Any new symptom involving a sudden change in the number of flashes, an increase in floaters, or a loss of peripheral vision should be treated as a medical emergency.
Medical Evaluation and Treatment Options
Patients presenting with new onset flashes and floaters require a comprehensive eye examination to determine the cause. The diagnostic procedure is the dilated fundus examination, where the ophthalmologist uses specialized lenses to view the entire retina, especially the peripheral edges where tears most often occur. This allows the doctor to check for signs of a retinal tear, detachment, or hemorrhage.
If the examination confirms an uncomplicated PVD, the only management necessary is observation and patient education about the warning signs of a tear. For a diagnosed retinal tear without detachment, the treatment is typically an outpatient procedure using a laser or cryopexy (freezing). These methods seal the edges of the tear, preventing fluid from causing a full detachment. If a retinal detachment has already occurred, surgical intervention is necessary, involving procedures like a vitrectomy to remove the vitreous gel or scleral buckling, where a silicone band is placed on the outside of the eye.