Seeing flashes of light, medically known as photopsia, is a visual symptom that warrants serious attention from a medical professional. Photopsia involves perceiving light that is not actually present in the external environment. These flashes are internal signals, originating from a stimulation of the light-sensing structures in your eye or brain. While the causes range from common, age-related changes to urgent, sight-threatening conditions, any new or sudden onset requires prompt evaluation. Understanding the difference between these causes is the first step toward protecting your vision.
Understanding Flashes of Light (Photopsia)
Photopsia occurs when the retina, the thin layer of nerve tissue lining the back of the eye, is stimulated by something other than light entering the pupil. This stimulation can be mechanical, such as physical tension or tugging on the retina, or it can be neurological, originating from the visual cortex in the brain. The retina reacts to this abnormal stimulation by sending an electrical impulse to the brain, which the brain interprets as a flash of light.
These flashes can manifest in various ways, often described as streaks, sparks, lightning bolts, or a camera flash. They are typically momentary and often noticed in the peripheral field of vision, especially in dim lighting. Photopsia is frequently reported alongside floaters, which are shadows cast onto the retina by tiny clumps of debris or condensed gel inside the eye. Floaters look like specks, cobwebs, or threads that drift through the vision.
Common Causes That Are Not Emergencies
The most frequent cause of new flashes and floaters is Posterior Vitreous Detachment (PVD), a benign, age-related process. The eye is filled with a gel-like substance called the vitreous humor, which naturally shrinks and liquefies with age. As the vitreous shrinks, it separates and pulls away from the retina, a process that happens to nearly everyone.
The flashes occur because the vitreous gel is still lightly attached to the retina in certain spots as it pulls away, causing a temporary mechanical tugging. This traction excites the retinal cells, creating the perception of light flashes, which are typically seen as arcs or lightning streaks in the side vision. Once the vitreous fully separates, the flashes generally subside, though the entire process can take a few days or weeks.
Flashes can also be caused by neurological events, most commonly a migraine with aura. These visual disturbances are not caused by retinal tugging but by a wave of electrical or chemical activity moving across the visual cortex in the brain. The flashes in a migraine aura are often described as shimmering, zigzagging lines, or a scintillating scotoma, and they typically affect both eyes simultaneously. They usually last between five minutes and one hour and may appear without a subsequent headache.
Mechanical stimulation, such as rubbing the eye firmly or receiving a hard blow to the head, can also generate temporary flashes. These flashes, called phosphenes, result from direct pressure on the photoreceptors in the retina. While brief, the perception of “seeing stars” after an impact can sometimes indicate a concussion, which requires immediate medical attention.
Urgent Conditions Requiring Immediate Care
While PVD is common and usually harmless, the pulling action of the vitreous can sometimes be forceful enough to cause a tear in the retina. A sudden, dramatic increase in the frequency or intensity of flashes, often accompanied by a shower of new floaters, can be a warning sign of a retinal tear. This is an urgent situation because fluid from the eye can leak through the tear and begin to separate the retina from its underlying supportive tissue.
This separation is known as a retinal detachment, a medical emergency that can lead to permanent vision loss if not promptly treated. Symptoms of detachment include a noticeable shadow, curtain, or veil moving across the field of vision, which corresponds to the area of the retina that has pulled away. The flashes associated with a tear or detachment are often described as sudden, bright, and camera flash-like, occurring repeatedly.
Vitreous hemorrhage, which is bleeding into the vitreous cavity, is another serious condition that can cause photopsia and a sudden onset of dark floaters. This bleeding occurs when retinal vessels tear during the vitreous separation process. A sudden increase in dark spots, which patients may describe as a “shower of dots” or “soot rain,” combined with flashes, suggests a tear accompanied by bleeding. Any combination of new flashes, new floaters, and a shadow over the vision requires same-day emergency evaluation.
Seeking Professional Evaluation and Diagnosis
Because the symptoms of a harmless PVD are indistinguishable from those of a sight-threatening retinal tear or detachment, professional evaluation is non-negotiable. Anyone experiencing a sudden onset of flashes, especially when combined with a sudden increase in floaters, should seek a comprehensive dilated eye exam within 24 hours. The initial assessment is typically performed by an ophthalmologist, who is a medical doctor specializing in eye care.
The diagnostic process involves dilating the pupil with eye drops to allow the doctor to get a clear, wide view of the entire retina, particularly the periphery where tears often occur. The doctor will use specialized lenses and instruments to examine the vitreous and the full extent of the retina to check for any tears, holes, or signs of detachment. Even if the flashes stop, the underlying cause, such as a retinal tear, may still be present and require treatment to prevent vision complications. If a tear is found, it can often be repaired with a simple outpatient procedure like laser treatment to seal the tear and prevent detachment.