Seeing flashes, streaks, or spots of light that do not come from an external source is a phenomenon medically known as photopsia. These visual sensations can be startling, especially when they appear suddenly or are more noticeable in the dark. While many people experience them as a harmless quirk of the visual system, flashes can also be a signal that requires urgent professional attention. The causes range from simple mechanical stimulation of the eye to age-related changes within the eye’s internal structure. Distinguishing between them often requires a comprehensive eye examination to know when to seek care and protect your vision.
How the Eye Registers Light Flashes
The eye’s ability to sense light resides in the retina, a thin layer of specialized, light-sensitive tissue lining the back of the eyeball. The retina contains millions of photoreceptor cells that convert light energy into electrical signals, which are then sent to the brain for interpretation as vision. When the retina is stimulated, it sends a message to the brain that is automatically processed as light, regardless of what caused the stimulation. This means the retina does not differentiate between actual incoming light and a physical or mechanical force acting upon it. When the tissue is pushed, pulled, or rubbed, it reacts by firing electrical impulses, creating the internal visual sensation of a flash.
Common Reasons for Temporary Flashes
Flashes that are brief and transient are often due to temporary, benign causes. Simply rubbing your eyes or applying gentle pressure can mechanically stimulate the retina, resulting in the perception of light, frequently described as “seeing stars.” This quick stimulation is called a pressure phosphene and usually resolves as soon as the pressure is removed. Another common source is the visual aura associated with a migraine headache, often referred to as an ocular migraine. These flashes typically appear as shimmering, jagged lines or arcs of light that gradually expand, often affecting both eyes. Unlike retinal stimulation, migraine auras originate in the visual processing centers of the brain and usually last between 20 and 30 minutes. Phosphenes can also occur temporarily during a sudden drop in blood pressure, such as when standing up too quickly.
When Vitreous Changes Cause Flashes
The most frequent cause of persistent or recurring flashes, especially in individuals over 50, relates to changes in the vitreous humor, the clear, gel-like substance that fills the main cavity of the eye. As a normal part of aging, this gel begins to liquefy and shrink, a process called vitreous syneresis. The gel’s outer layer, which is attached to the retina, eventually pulls away from the back wall of the eye in a process known as Posterior Vitreous Detachment (PVD).
When the vitreous gel pulls away, it can exert a slight tugging or traction on the delicate retinal tissue. This mechanical stress on the photoreceptor cells generates the visual signal, which the brain interprets as a flash of light. These flashes are often described as brief streaks of lightning or camera flashes, and are typically more noticeable in the peripheral vision or in dim light. For most people, PVD is a common, non-sight-threatening event that simply requires monitoring.
Retinal Tears and Detachment
In a small percentage of cases, the vitreous is more strongly attached to the retina. If the gel pulls too forcefully, it can create a small break or tear in the retinal tissue. A retinal tear is a serious complication because fluid from the vitreous cavity can seep through the break, lifting the retina away from its underlying support layers. This separation is a retinal detachment, which can lead to permanent vision loss if not treated promptly.
Urgent Symptoms and Seeking Care
The presence of any new onset of flashes requires a dilated eye examination to rule out a retinal tear or detachment. This check-up should occur quickly, even if the flashes seem minor, as a retinal tear can often be treated with a simple in-office procedure if caught early. Immediate and urgent care is required if you experience a sudden increase in the number or intensity of flashes. Another red flag symptom is a sudden shower of new floaters, which may look like specks, cobwebs, or pepper suddenly appearing in your vision. The most serious warning sign is the perception of a gray shadow, curtain, or veil obscuring any part of your peripheral or central vision, as this often indicates a retinal detachment. If any of these acute symptoms occur, seek immediate evaluation from an eye care professional or an emergency department.