Flashes of light seen in the corner of the eye, medically termed photopsia, are a common visual disturbance. While these flashes can sometimes be harmless, they always necessitate professional medical evaluation to rule out conditions that threaten vision. This article will explain the underlying biology of photopsia and help distinguish between less serious and more urgent causes.
The Anatomical Reason for Seeing Flashes
The physical sensation of seeing a flash of light originates from the retina, the eye’s primary light-sensing tissue, and the vitreous humor, the clear, gel-like substance filling the eye’s interior. The vitreous is attached to the retina, which lines the back of the eye and converts light into electrical signals sent to the brain. Over time, the vitreous naturally begins to shrink and liquefy, a process that can cause it to pull or tug on the retina.
This mechanical stimulation irritates the retinal cells, causing them to fire an electrical impulse. The brain interprets this impulse as a flash or streak of light, mistaking the stimulation for an actual external light source. These flashes are often described as brief, like a camera flash or a streak of lightning, and are typically most noticeable in the peripheral vision. The flashes may also be more evident when moving the eye or when in a dark environment.
Causes That Are Not Immediate Emergencies
Many instances of photopsia are caused by Posterior Vitreous Detachment (PVD). By the age of 65, approximately 75% of people will develop PVD, where the vitreous gel cleanly separates from the retina. This separation can cause new flashes of light and floaters, but PVD itself does not typically cause permanent vision damage.
The flashes associated with PVD tend to diminish over time as the vitreous completely detaches. However, an eye examination is still required because the initial symptoms of PVD are nearly identical to those of a retinal tear.
Another common, non-retinal cause of flashes is a migraine aura, sometimes called an ocular migraine. These visual disturbances are neurological in origin, affecting the visual processing center of the brain. They typically appear as shimmering, jagged lines or an expanding blind spot.
Migraine auras usually affect both eyes simultaneously and can last anywhere from five minutes to an hour, often resolving completely. Flashes caused by a retinal issue, conversely, are typically restricted to only one eye. Flashes can also be generated by simple mechanical stimulation, such as rubbing the eyes vigorously or experiencing a sudden blow to the head, which causes a temporary physical force on the retina.
Recognizing the Signs of a Retinal Emergency
The concern with new or changing flashes and floaters is that the tugging of the vitreous on the retina can sometimes be strong enough to create a break in the tissue, leading to a retinal tear. This tear is often signaled by a sudden onset of new symptoms. The flashes are usually more persistent and intense, and they are accompanied by a sudden “shower” of many new floaters, often described as black spots, cobwebs, or pepper shaken into the vision.
If a retinal tear is left untreated, the fluid from the vitreous humor can seep through the opening and accumulate underneath the retina, causing a retinal detachment. When detached, the retina is lifted away from the underlying tissue that provides it with oxygen and nourishment.
Retinal detachment is a medical emergency signaled by distinct visual symptoms beyond flashes and floaters. Patients frequently report a shadow, curtain, or veil moving across their field of vision, representing the area of the retina that has become detached.
This progressive loss of vision, often starting in the peripheral vision, is a sign that the condition is advancing and requires immediate attention. Unlike temporary, bilateral migraine flashes, the symptoms of a retinal tear or detachment are localized to one eye and progressively worsen. Prompt treatment of a retinal tear is the best defense against a full retinal detachment.
Diagnosis and Necessary Next Steps
Any sudden onset of new flashes or floaters, especially if accompanied by a shower of black spots or a shadow in the vision, requires urgent medical evaluation. The time frame for seeking care is typically within 24 hours of the symptoms beginning, as early intervention significantly improves the prognosis for preserving vision.
An eye care professional, such as an optometrist or ophthalmologist, will perform a comprehensive, dilated eye exam. Dilation uses eye drops to widen the pupil, allowing the doctor to clearly see the entire retina. If a clear view is obstructed, such as by bleeding in the vitreous, an ophthalmic ultrasound may be used to assess the retina’s condition.
If a retinal tear is diagnosed before it progresses to a detachment, the treatment is often a quick, in-office procedure. This uses either a laser, called photocoagulation, or a freezing technique, called cryopexy. Both methods work by creating scar tissue around the tear to “weld” the retina to the underlying tissue, sealing the break and preventing fluid from leaking through. If a full retinal detachment has occurred, more involved surgical procedures are necessary, such as injecting a gas bubble or performing a vitrectomy to reattach the retina.