The experience of seeing flashes, streaks, or patterns of light when your eyes are closed is a common phenomenon. These visual sensations occur even without external light entering the eye. They are generally referred to as photopsia, though the term phosphenes is often used for flashes caused by non-light stimuli. Understanding the source of these internal lights helps determine if the cause is harmless or requires medical attention.
The Science Behind Internal Light Perception
The brain interprets signals from the optic nerve as light, regardless of the trigger. The retina, located at the back of the eye, contains specialized photoreceptors that convert light into electrical signals. When the eyes are closed, these photoreceptors can still be activated by other forms of energy. Phosphenes are the visual sensations resulting from mechanical, electrical, or magnetic stimulation of the retina or the brain’s visual pathways. Physical pressure on the eyeball, for instance, can mechanically stimulate the photoreceptors, causing them to fire an impulse that the brain processes as light.
Everyday Causes of Harmless Flashes
The most frequent and non-threatening reason for seeing internal flashes is direct pressure on the eyeball, known as pressure phosphenes. Rubbing your eyes, a common habit, mechanically stimulates the retina, causing a temporary burst of light perception that quickly fades when the pressure is removed. These pressure-induced flashes are short-lived and typically appear as diffuse colored patches or bright shapes.
Other common causes relate to sudden changes in blood flow or physical force. Standing up too quickly, for example, can cause a brief drop in blood pressure, resulting in a temporary visual disturbance described as “seeing stars.” A heavy cough, sneeze, or a blow to the head can also generate phosphenes due to the mechanical forces involved. These flashes are usually transient and do not suggest underlying damage to the eye’s structure.
Serious Conditions Associated with Flashing Lights
Flashes that are persistent, sudden, or accompanied by other visual changes are known as photopsia and may indicate a problem within the eye itself. The most frequent pathological cause is Posterior Vitreous Detachment (PVD), a natural, age-related process where the vitreous gel filling the eyeball shrinks and pulls away from the retina. As the gel pulls on the light-sensitive retina, it causes the photoreceptors to fire, resulting in the perception of brief, white, or golden-yellow streaks of light, often seen in the peripheral vision.
A more serious concern arises if the vitreous gel pulls hard enough to tear the retina, which can lead to a Retinal Detachment. Flashes from a detachment are often described as a shower of sparks or lightning strikes that appear suddenly and may intensify with eye movement. A detached retina separates from the underlying tissue that provides it with oxygen and nutrients, making this a medical emergency. A sudden increase in floaters, along with a dark shadow or a curtain moving across the field of vision, are severe warning signs of a retinal tear or detachment.
Flashes can also be a symptom of a neurological event, such as a Migraine Aura. This temporary visual disturbance precedes a headache and typically affects both eyes. Migraine aura flashes are often seen as complex, shimmering lights, zigzag lines, or a gradually expanding blind spot. These visual symptoms, sometimes called scintillating scotomas, usually last less than 60 minutes and are not caused by a problem with the retina.
What to Do If You Experience Persistent Flashes
If you experience the occasional, fleeting flash after rubbing your eyes or standing up quickly, these are generally considered harmless phosphenes. However, any new onset of flashes that are persistent, frequent, or occur without mechanical stimulation warrants an immediate evaluation by an eye care professional. The sudden appearance of many new floaters, especially if accompanied by flashes, is a red flag symptom that needs urgent attention.
An urgent eye examination is necessary to rule out a retinal tear or detachment, which are sight-threatening conditions requiring timely intervention. The doctor will perform a dilated eye exam, using drops to widen the pupil, allowing them to thoroughly inspect the retina and vitreous gel. Early detection of a retinal tear often allows for treatment with laser or freezing procedures to prevent a full detachment.