Photopsia, more commonly known as eye flashes, is the perception of light that occurs when there is no external light source present. These visual disturbances may manifest as streaks of lightning, brief bursts, or sparkling lights. While occasional flashes are often a common occurrence, particularly with age, this symptom can signal a serious, time-sensitive problem affecting vision, requiring prompt professional evaluation is always necessary.
The Mechanism Behind Eye Flashes
The primary cause of light flashes originates from the mechanical stimulation of the retina, the light-sensitive tissue at the back of the eye. The interior of the eyeball is largely filled with the vitreous gel, a clear, jelly-like substance. As a person ages, this gel naturally liquefies and shrinks, a process known as syneresis. This change causes the vitreous to pull away from the retina, which is typically a gradual event called a Posterior Vitreous Detachment (PVD).
When the shrinking vitreous tugs on the retina, the mechanical force is interpreted by the brain as a visual signal, specifically a flash of light. The retina’s photoreceptor cells fire in response to this physical tension, creating the illusion of light. These flashes are usually noticed more easily in low-light conditions. In most cases, the vitreous separates completely without causing harm, and the flashes eventually subside.
Urgent Warning Signs Requiring the Emergency Room
Certain flash symptoms are considered an ophthalmologic emergency and require immediate evaluation at an emergency room or a specialized eye clinic. The most severe concern is a retinal tear or detachment, where the retina pulls away from the underlying tissue, risking permanent vision loss. A sudden, dramatic onset of new, persistent flashes of light, especially when concentrated in the peripheral vision, indicates severe traction on the retinal tissue.
This type of emergency is often accompanied by a sudden “shower” of new floaters, which may look like black spots, specks, or “soot.” This sudden increase can be caused by blood or pigment cells released when the retina tears. Another symptom demanding immediate emergency attention is the appearance of a gray curtain or shadow that blocks part of the visual field. This obscuration represents the area of the retina that has detached and is no longer functioning. Any flashes that occur immediately following a direct injury or blunt force trauma to the eye or head should also prompt an immediate emergency visit. Time is a factor in preserving vision when a retinal detachment or tear is suspected.
Situations That Need Prompt Non-ER Evaluation
Not all flashes indicate an immediate, sight-threatening emergency, but they still require prompt evaluation, typically within 24 to 48 hours. One common non-retinal cause is a migraine with visual aura, sometimes called an ocular migraine. These flashes often appear as shimmering, zigzag lines or arcs of light that gradually expand and usually affect both eyes simultaneously. The visual disturbance from a migraine aura typically lasts less than 30 minutes and may or may not be followed by a headache.
Flashes that are mild, occasional, and have been previously evaluated and attributed to a stable Posterior Vitreous Detachment (PVD) do not warrant an ER trip if the symptoms have not significantly changed. Phosphenes, or flashes caused by mechanical pressure like rubbing the eyes, are benign and do not require urgent care. However, because the symptoms of a benign PVD can overlap with a serious tear, any new or significantly worsening flash symptoms should still be evaluated quickly by an ophthalmologist or optometrist.
What to Expect During an Eye Examination
An eye examination for flashes begins with a detailed discussion of the symptoms, including when the flashes started, what they look like, and whether they are accompanied by floaters or vision loss. The practitioner will then perform a visual acuity test to check the sharpness of your vision. The primary diagnostic step is the dilated fundus examination, where specialized drops are used to widen the pupil.
Dilation allows the doctor to use a powerful lens and a bright light to inspect the entire retina, including the periphery, for any signs of tears, holes, or detachment. If a clear view of the retina is obstructed, perhaps by a vitreous hemorrhage, an ultrasound of the eye may be performed to visualize the retinal status. Depending on the findings, treatment may range from simple monitoring for a stable PVD to laser therapy for a small tear or surgery for a full retinal detachment.