The sensation of seeing “stars” or unexpected flashes of light is medically termed photopsia. This visual phenomenon is the perception of light where no external source exists, often described as streaks, sparkles, or lightning bolts. Photopsia is a symptom, not a condition itself, signaling that the visual system—either the retina or the brain—is being stimulated abnormally.
Common and Systemic Triggers
Brief flashes can often be traced to temporary changes in the body’s internal environment or minor mechanical forces applied to the eye. A frequent systemic cause is a sudden drop in blood pressure, known as orthostatic hypotension. This occurs when a person stands up too quickly, causing momentary hypoperfusion, or reduced blood flow, to the brain and retina. The resulting lack of oxygen or nutrients to the visual processing centers can trigger the perception of light, which resolves as circulation stabilizes.
Physical trauma to the head, often referred to as “seeing stars,” causes a transient form of photopsia. The mechanical force from the impact causes a spontaneous firing of neurons in the occipital lobe of the brain, which the brain interprets as flashes of light. This is generally a momentary event that subsides quickly after the trauma.
Another cause is the Valsalva maneuver, a forceful attempt to exhale against a closed airway, which happens during severe coughing, sneezing, or heavy lifting. This action sharply increases pressure, which is transmitted to the veins in the head and neck. This sudden rise in venous pressure can cause superficial retinal capillaries to rupture, a condition called Valsalva retinopathy, which may lead to floaters or painless vision loss. Dehydration can also contribute to transient flashes by affecting overall blood volume and circulation.
Eye-Specific Conditions Causing Photopsia
The most frequent causes of photopsia originate within the eye’s structure, involving the relationship between the vitreous gel and the retina. The vitreous is a clear, gel-like substance that fills the main cavity of the eye. It is attached to the retina, the light-sensitive tissue lining the back of the eye, by millions of microscopic fibers.
As a person ages, the vitreous gel naturally begins to liquefy and shrink, a process that can cause it to pull away from the retina. This traction on the retinal tissue mechanically stimulates the photoreceptor cells, causing them to send electrical impulses to the brain. Since the retina’s only function is to transmit light information, the brain interprets these mechanical signals as flashes of light, often appearing as quick streaks in the peripheral vision.
This age-related separation is known as a Posterior Vitreous Detachment (PVD), which is a common occurrence, affecting about 75% of people over the age of 65. PVD is the most common cause of photopsia, accounting for nearly 40% of cases in some studies. The flashes typically last less than a second and may become less frequent as the vitreous completely separates from the retina.
A more serious condition arises if the vitreous gel pulls too hard on the retina, causing a retinal tear or a retinal detachment. In this scenario, the flashes are more intense and prolonged because the retina is being stimulated as it is pulled away from the underlying tissue. If a tear occurs, fluid can seep behind the retina, causing it to separate from its metabolic support, which is a condition requiring immediate medical intervention.
Photopsia can also be neurological in origin, such as with a migraine aura. These visual disturbances are caused by a wave of altered electrical activity that spreads across the visual cortex of the brain. The flashes associated with a migraine aura often appear in both eyes, and are typically described as shimmering, zigzag lines or arcs of light that expand and move across the field of vision over 10 to 30 minutes. Unlike retinal flashes, migraine auras persist even when the eyes are closed, confirming their origin in the brain.
When to Seek Emergency Care
While many instances of photopsia are benign, certain symptoms signal a medical emergency requiring immediate ophthalmological evaluation. The most concerning scenario is a sudden onset of new or increased flashes, especially when accompanied by other visual changes. This combination of symptoms suggests a potential retinal tear or detachment.
A sudden “shower” of new floaters, which look like small specks, dark dots, or cobwebs, is a significant warning sign that often accompanies the increased flashes. These floaters can be debris released into the eye from the vitreous or, more alarmingly, blood cells from a torn retinal vessel.
The appearance of a dark shadow or a curtain-like obstruction descending over any part of the vision is a sign that the retina has detached. This visual field defect indicates that the light-sensing tissue is no longer functioning in that area. Prompt treatment for a retinal detachment, ideally within hours, is necessary to prevent permanent vision loss.