Seeing stars, flashes, or shimmering patterns in your vision is known as photopsia or phosphenes. This occurs when the retina or the visual processing centers of the brain are stimulated without an actual light source. The perception of light signals that the visual system has been mechanically, metabolically, or electrically excited. While these visual disturbances can be brief and harmless, they sometimes indicate an underlying condition requiring prompt medical attention.
Visual Disturbances Originating in the Eye
Flashes of light originating within the eye are usually caused by physical changes or traction on the retina. The retina is a thin layer of tissue lining the back of the eye that interprets any stimulation as light. When the vitreous humor, the gel-like substance filling the eyeball, changes, it can mechanically pull on the retina, causing a flash of light.
This process often begins with a Posterior Vitreous Detachment (PVD), a common, age-related event where the vitreous naturally shrinks and separates from the retina. The microscopic fibers connecting the vitreous to the retina can tug on the tissue as the gel liquefies and separates. The brain interprets this tugging action, typically seen in the peripheral vision, as a flash or streak of light.
If the vitreous tugs too hard on an area where it is firmly attached, it can cause a Retinal Tear. A tear allows fluid to pass beneath the retina, causing it to separate from the underlying blood vessel layer, resulting in a Retinal Detachment. This physical separation causes the retinal cells to cease functioning properly, leading to symptoms like a sudden increase in flashes and floaters, or the appearance of a dark curtain blocking vision. This condition is an emergency because the retina loses its blood supply and can result in permanent vision loss if not repaired quickly.
A neurological visual disturbance is the visual aura without headache, sometimes referred to as an ocular migraine. This event is caused by a wave of abnormal electrical activity, called cortical spreading depolarization, moving across the visual cortex. Symptoms typically affect both eyes and present as shimmering, zigzag lines, or an expanding blind spot. These disturbances usually last between 5 and 60 minutes before resolving completely.
Systemic Conditions Affecting Vision
Visual disturbances can also stem from issues outside the eye, primarily related to blood flow, metabolism, or physical trauma. Seeing stars upon standing up quickly is a classic example of Orthostatic Hypotension, a sudden drop in blood pressure. When the body changes position rapidly, gravity pulls blood downward. If the body’s compensatory mechanisms are too slow, the brain and retina experience a temporary lack of oxygen and blood flow, causing the momentary perception of stars until blood pressure stabilizes.
Another systemic cause is Hypoglycemia, or low blood sugar, which starves the brain and retina of their primary energy source, glucose. The retina is particularly sensitive to this lack of glucose due to its high metabolic rate. This energy deprivation can lead to symptoms like blurred vision or a central blind spot. These visual disturbances resolve once blood glucose levels are restored to a normal range.
A classic Migraine with Aura is differentiated from a visual aura without headache by the accompanying severe head pain. The visual aura is the result of cortical spreading depolarization, an electrical wave moving across the brain’s surface. Symptoms, which can include flashes, shimmering spots, or a scotoma (blind spot), often precede the headache by 10 to 60 minutes. A sharp blow to the head, such as a Concussion, can cause a transient episode of seeing stars due to the temporary disruption of the visual processing centers.
Identifying Urgent Symptoms
While many causes of photopsia are benign, certain associated symptoms indicate a medical emergency that requires immediate evaluation by an ophthalmologist. The most significant red flag is the sudden onset or a rapid, dramatic increase in the number of flashes and floaters. This sudden change strongly suggests that the vitreous gel is actively pulling on the retina, raising the risk of a tear.
The appearance of a dark shadow, a gray cloud, or a curtain-like obstruction in any part of the field of vision is a symptom of a possible retinal detachment. Since a detached retina is painless, this visual obstruction is often the only sign that the retina has physically separated from its necessary blood supply. Any flashes or visual changes that occur after a direct injury or trauma to the eye or head should also be evaluated promptly.
Other concerning symptoms include visual changes that affect only one eye, as this is more likely to indicate a problem with the retina or optic nerve rather than a migraine aura. If the flashes are accompanied by severe eye pain, nausea, or a sudden, unexplained loss of peripheral vision, immediate professional consultation is necessary. Seeking prompt attention for these specific symptoms can prevent permanent vision loss in the event of a treatable condition.