Seeing lights in the corner of your eye, medically known as photopsia, can be alarming. These visual phenomena are typically described as flashes, streaks, or sparks of light appearing without an external source. Photopsia is not a disease but a sign that the eye’s light-sensitive tissues or the brain’s visual processing centers are being stimulated. While often benign and related to the natural aging process, photopsia can also signal serious, sight-threatening conditions. Understanding the origin of these flashes is necessary because some causes require immediate evaluation and treatment.
Flashes Caused by Changes in the Vitreous Gel
The most frequent cause of peripheral light flashes stems from changes within the eye’s internal structure. The eye’s main cavity is filled with the vitreous humor, a clear, gel-like substance attached to the retina. As a person ages, this gel naturally begins to liquefy and shrink, a process called syneresis. This age-related change causes the vitreous gel to separate from the retina, known as Posterior Vitreous Detachment (PVD).
Flashes occur during this separation because the shrinking vitreous tugs on the retina. Since the retina interprets light, this mechanical stimulation causes photoreceptor cells to fire electrical impulses, which the brain perceives as flashes. These flashes are usually quick, white or golden streaks noticed in the peripheral visual field, especially in dim lighting. PVD is common, affecting over 50% of people by age 80. While the flashes typically diminish once the separation is complete, the initial phase requires monitoring to ensure the traction does not damage the retina.
Urgent Causes: Retinal Tears and Detachment
Although PVD is a routine part of aging, forceful vitreous separation can sometimes cause an emergency. If the vitreous is strongly adhered to the retina, the mechanical traction may pull retinal tissue away, creating a tear or hole. A retinal tear is serious because it allows fluid from the eye cavity to seep underneath the retina.
This fluid accumulation can lift the retina away from the underlying tissue that supplies oxygen and nutrients, leading to a retinal detachment. The flashes associated with a tear or detachment are often more intense, sudden, and persistent than those from uncomplicated PVD. They may also be accompanied by a rapid increase in floaters. A key symptom of detachment is the appearance of a dark shadow or a curtain moving across the field of vision.
Visual Disturbances Related to Neurological Conditions
Not all perceived light flashes originate from mechanical issues within the eye; some are neurological. The most common is the visual aura associated with a migraine, which can occur with or without a headache. Migraine aura is caused by a wave of abnormal electrical activity spreading across the visual cortex in the brain.
These visual disturbances differ distinctly from flashes caused by vitreous traction. Migraine aura often manifests as shimmering, zigzag lines, or geometric patterns that begin near the center of vision and expand outward. Unlike peripheral retinal flashes, these neurological lights usually affect both eyes simultaneously and last temporarily, generally 10 to 30 minutes, before resolving. Less commonly, photopsia can signal other neurological conditions, such as optic neuritis or issues related to blood flow to the visual pathways.
When to Seek Immediate Ophthalmic Care
Any sudden onset of new flashes or floaters requires a prompt, comprehensive eye examination, as timely intervention is crucial for preserving vision. An increase in the number of flashes or floaters is a significant warning sign. Urgency is especially pronounced if the flashes are accompanied by a noticeable decrease in vision, a shadow, or a curtain-like obstruction in the visual field.
These symptoms suggest a retinal tear or detachment, necessitating evaluation by an eye specialist within 24 hours. The specialist, typically an ophthalmologist, will perform a dilated eye exam to thoroughly inspect the retina for damage. Early detection allows for preventive treatments, such as laser therapy, which can seal a tear and prevent a full retinal detachment. Acting quickly upon observing these specific signs increases the potential for a successful outcome and preservation of sight.