The sudden perception of a flash of light inside the eye, known as photopsia, can be a startling experience. Photopsia is the sensation of light, streaks, or sparks that appear in the visual field without an external light source. These flashes are electrical signals generated within the visual system itself. Understanding the source of these internal signals is important, as the causes range from common, age-related changes to sight-threatening emergencies that require immediate attention.
How the Vitreous Gel Creates Flashes
The most frequent cause of these bursts of light is a change involving the vitreous gel. The vitreous humor is a clear, jelly-like substance that fills the central cavity of the eyeball and is loosely attached to the retina, the light-sensitive tissue lining the back of the eye. As a person ages, this gel naturally begins to liquefy and shrink, causing it to separate from the retina’s surface. This separation is called a Posterior Vitreous Detachment (PVD).
During this separation, the shrinking vitreous gel can mechanically tug on the retina, which is composed of photoreceptor cells. This mechanical stimulation irritates the retinal cells, causing them to discharge electrical impulses. The brain interprets these impulses as brief streaks of light, often appearing white or golden yellow. These flashes often appear in the peripheral vision and may be more noticeable when the eyes are moved or in dim lighting. In most individuals, PVD is a normal, harmless part of aging that resolves once the vitreous fully detaches.
Flashes Indicating Retinal Damage
While flashes associated with a clean Posterior Vitreous Detachment typically subside, excessive mechanical pulling can lead to serious complications. The retina has areas firmly attached to the vitreous, and excessive traction at these points can cause the delicate tissue to tear. A retinal tear is serious because fluid from the vitreous cavity can pass through the opening and accumulate beneath the retina. This fluid accumulation causes the retina to peel away from the underlying tissue, resulting in a retinal detachment.
Symptoms indicating a retinal tear or detachment differ from a simple PVD because they represent an active, destructive process. A sudden, dramatic increase in the number and intensity of flashes, often described as a burst of lightning, is a major warning sign. This is frequently accompanied by a shower of new floaters, which are dark spots or specks that drift across the vision. The most concerning symptom is the appearance of a shadow or a “curtain” that moves into the field of vision, representing the detached area. These symptoms signify a medical emergency, as a detached retina can lead to permanent vision loss if not repaired rapidly.
Flashes Related to Migraines and Circulation
Not all flashes of light originate from a structural issue within the eye; some are neurological events that begin in the brain’s visual processing center. The most common non-ocular cause is a visual migraine aura, which can occur with or without a headache. This visual disturbance is caused by a wave of altered electrical activity spreading across the brain’s visual cortex. The perception of light typically affects both eyes simultaneously and is characterized by shimmering, jagged lines, or zigzag patterns.
These patterned flashes, sometimes called fortification spectra, usually expand gradually and resolve completely within 10 to 30 minutes. Migraine aura phenomena are distinct because they are symmetrical and move across the central visual field, unlike flashes from vitreous traction, which are typically brief and limited to the side vision of one eye. Other systemic issues can also trigger photopsia, such as sudden drops in blood pressure that temporarily affect blood flow to the optic nerve or retina.
Seeking Professional Evaluation
Any new onset of photopsia warrants a professional examination, even if the flashes are brief or appear mild. Only an eye care professional can definitively determine if the symptoms are due to a benign vitreous separation or a sight-threatening tear. The presence of “red flag” symptoms requires immediate, same-day attention to prevent permanent damage.
Urgent Signs
Urgent signs include:
- A sudden, high frequency of flashes.
- A large increase in new floaters.
- Any loss of peripheral or central vision.
A comprehensive eye examination involves pupil dilation, allowing the doctor to use specialized instruments to look directly at the entire retina. This dilated exam is the only reliable way to check for a small retinal tear that may not yet be causing a full detachment. Early diagnosis allows for treatment with minimally invasive procedures like laser therapy or cryotherapy, which can seal the tear and prevent progression to a retinal detachment. While many instances of light flashes are harmless, a prompt evaluation ensures that serious conditions are ruled out or treated quickly.