Flashes of light that appear in your vision, often described as streaks of lightning or camera flashes, are a visual phenomenon known as photopsia. These light perceptions are not caused by external light sources but are generated internally within the eye or the brain. Photopsia is a symptom, indicating that something is mechanically or electrically stimulating the visual system. While these internal light shows are common, their sudden onset or change in character warrants attention because they can signal both harmless age-related changes and sight-threatening emergencies.
The Mechanical Source of False Light
The eye is designed to interpret signals from the retina as light, regardless of what generated the signal. The retina is the light-sensitive tissue lining the back of the eye, and its photoreceptor cells send electrical impulses to the brain. Usually, these impulses are triggered by photons, or actual light, entering the eye. However, the retina’s neural tissue is sensitive enough that mechanical irritation can also cause it to fire an electrical signal. When the retina is physically stimulated by a tugging or pulling force, the brain interprets the resulting electrical impulse as a sudden flash or streak of light, similar to “seeing stars” after a blow to the head.
Age-Related Changes in the Vitreous Gel
The most frequent cause of flashes is a natural aging process that occurs within the eye. The main cavity of the eye is filled with a clear, jelly-like substance called the vitreous humor, which is firm and attached to the retina in youth. As a person ages, the vitreous gel begins to liquefy and shrink, causing it to pull away from the retinal surface. This separation is known as Posterior Vitreous Detachment (PVD), a normal occurrence that affects most people over age 65. As the shrinking gel peels away, it briefly tugs on the retina at the points of attachment, which mechanically stimulates the tissue and causes the characteristic brief flashes. These flashes typically last for a few weeks to months until the vitreous successfully separates from the retina, but every case requires an eye examination to ensure the separation is uncomplicated.
Retinal Tears and Detachment
A more serious cause of flashes occurs if the vitreous gel is abnormally adherent to the retina. In these cases, the force of the shrinking gel can pull too hard on the delicate retinal tissue, creating a full-thickness tear or hole. A retinal tear is dangerous because it allows fluid from the center of the eye to seep through the opening and accumulate underneath the retina. This fluid pressure lifts the retina away from its underlying blood supply, resulting in a sight-threatening condition known as retinal detachment. Flashes associated with a tear or detachment are often sudden, persistent, and accompanied by a rapid increase or “shower” of new floaters.
Triage: When Flashes Signal an Emergency
Any sudden onset of flashes or floaters requires a prompt, comprehensive eye examination to rule out a retinal tear or detachment. Specific “red flag” symptoms necessitate an immediate emergency assessment within 24 hours. These include the sudden appearance of a shower of new floaters, a marked increase in the frequency of flashes, or any loss of vision. A particularly urgent symptom is the perception of a dark curtain, veil, or shadow moving across the field of vision, which suggests a retinal detachment is already occurring. While flashes caused by ocular migraines are a non-mechanical differential diagnosis, appearing as shimmering, jagged lines that affect both eyes, it is safest to assume the symptoms are serious until proven otherwise.