Photopsia is a common visual symptom characterized by seeing flashes of light when no external source is present. This phenomenon can manifest as brief streaks, sparks, or flickering lights in the field of vision. While many causes are not sight-threatening, photopsia can signal a severe condition requiring urgent intervention. Any sudden onset or change in these visual flashes must be evaluated immediately by an eye care professional, such as an ophthalmologist or optometrist, to determine the underlying cause and protect vision.
The Physics of Light Flashes
The experience of photopsia occurs because the brain interprets any electrical signal from the retina as light, even if no light waves caused the signal. This visual sensation, known as a phosphene, is not triggered by photons. The retina, the light-sensitive tissue at the back of the eye, is composed of photoreceptor cells that convert light into electrical impulses sent to the brain.
When the retina is stimulated mechanically, rather than optically, these photoreceptors fire an impulse. This mechanical stimulation is caused by physical tension, pressure, or movement exerted directly on the delicate retinal tissue. The resulting electrical burst travels along the visual pathway, causing the brain to mistakenly perceive a flash, spark, or streak of light.
Common Ocular Causes and Associated Symptoms
The most frequent cause of new flashes and floaters is Posterior Vitreous Detachment (PVD), an age-related process. The vitreous is a gel-like substance filling the eye’s main cavity that naturally shrinks and liquefies over time, eventually separating from the retina. When the vitreous separates, the remaining attachments can temporarily tug on the retina, causing the brief, electrical discharge perceived as flashes.
These flashes are typically short-lived, rapid bursts, similar to a camera flash or a lightning streak, and are often seen in the peripheral vision of one eye. While PVD is a natural occurrence, the tugging action can sometimes lead to a retinal tear, which requires a thorough eye examination.
Flashes can also originate from neurological events, most notably an ocular migraine, also known as a migraine with aura. Unlike PVD-related flashes, migraine aura usually presents as shimmering, zigzag lines, or geometric patterns that may slowly expand across the field of vision. These visual disturbances are often bilateral, occurring in both eyes simultaneously, and can last for a period of 10 to 30 minutes before resolving completely.
Other less common causes of photopsia include intraocular inflammation, such as uveitis, which causes the appearance of flashes and floaters. Changes in ocular pressure or blood flow, such as when standing up too quickly, can also induce brief, transient flashes.
When Flashes Indicate a Medical Emergency
A sudden increase in the frequency or intensity of flashes, especially when combined with other symptoms, can signal a severe medical condition like a Retinal Detachment. This occurs when the retina peels away from the underlying tissue that provides it with oxygen and nutrients. When the retina is pulled or torn, it generates a barrage of electrical signals, leading to intense or rapidly increasing flashes.
A detachment is frequently preceded or accompanied by a sudden “shower” of new floaters, which may be described as a cloud of pepper flakes, soot, or cobwebs. The most alarming symptom is the appearance of a shadow or a “curtain” that descends or moves across the field of vision, representing the area where the retina has fully detached.
These symptoms require immediate evaluation, often within hours, because delaying treatment significantly increases the risk of permanent vision loss. Treatment options range from laser therapy to seal a small tear, to surgical procedures like a vitrectomy or scleral buckle to reattach the retina and preserve sight.