“Seeing stars” describes phosphenes, which are visual sensations of light that are not caused by light actually entering the eye. These flashes, dots, squiggles, or colored patterns are generated when the light-sensitive cells of the retina or the visual processing centers of the brain are stimulated by non-light means. This stimulation can be mechanical, electrical, or metabolic, sending a false signal to the brain that is interpreted as light. While phosphenes are often temporary and harmless, like those experienced after rubbing your eyes, their sudden or persistent appearance can signal a serious underlying condition affecting the eye or the central nervous system. Understanding the different triggers is important for determining whether the symptom is benign or requires prompt medical evaluation.
Common Temporary Causes
Phosphenes can be caused by simple, transient physical events that quickly resolve without intervention. One common trigger is a temporary drop in blood pressure, known as postural hypotension, which occurs when a person stands up too quickly. The rapid shift in posture momentarily reduces blood flow to the brain and eyes, causing a lack of oxygen that manifests as a brief visual disturbance.
Minor mechanical trauma to the eye is another frequent cause of seeing stars. Rubbing the eyes or sustaining a minor bump to the head can directly stimulate the retina’s photoreceptor cells, resulting in the perception of light. This pressure-induced phenomenon is typically short-lived and ceases once the external force is removed.
Physical strain from forceful actions like hard coughing, sneezing, or intense straining can also increase eye pressure enough to stimulate the retina. These brief, self-limiting episodes are generally not a cause for concern and disappear as the pressure quickly equalizes.
Issues Originating Within the Eye
Visual flashes that originate within the eye itself are often related to changes in the vitreous humor, the clear, gel-like substance filling the eyeball. As people age, this gel naturally liquefies and shrinks, eventually pulling away from the retina in a process called Posterior Vitreous Detachment (PVD). PVD is a very common condition, occurring in about 75% of people over the age of 65.
The flashes of light, or photopsia, occur because the shrinking vitreous gel tugs on the retina. Since the retina contains no pain receptors, this mechanical stimulation is interpreted by the brain as a flash or streak of light, often described like a camera flash in the peripheral vision. When the vitreous fully separates, the pulling stops, and the flashes typically subside over a period of weeks or months.
However, the traction from the vitreous on the retina can sometimes be strong enough to cause a Retinal Tear or Retinal Detachment. A retinal tear is a serious event because it allows fluid to seep underneath the retina, pushing it away from the underlying blood supply and potentially leading to permanent vision loss if untreated. The flashes caused by a tear tend to be more numerous, intense, and persistent than those from a simple PVD, and they often appear alongside a shower of new floaters.
Systemic and Neurological Triggers
Phosphenes can also be a symptom of conditions originating outside the eye structure, primarily involving the brain’s visual pathways or systemic health issues. Ocular migraines, also known as migraines with aura, produce visual disturbances that are generated in the visual cortex of the brain. The aura phase of a migraine often presents as shimmering, zigzag lines, or geometric patterns that expand across the field of vision, lasting for up to 30 minutes.
These neurological flashes are different from retinal flashes because they are often seen with both eyes open and closed, suggesting a brain origin. Another systemic cause is hypoglycemia, or low blood sugar, which can trigger the neurological events that lead to a migraine-like aura. The brain relies heavily on glucose for energy, and a significant drop can disrupt normal function, leading to visual symptoms.
Severe fluctuations in blood pressure, such as a hypertensive crisis or severe hypotension, can also affect blood flow to the visual centers, leading to phosphenes. More serious neurological events like a Transient Ischemic Attack (TIA) or stroke can cause sudden visual field loss or flashes due to disrupted blood supply to the visual cortex. In these cases, the visual symptoms are typically accompanied by other neurological signs.
Warning Signs Requiring Immediate Medical Attention
While many causes of seeing stars are harmless, specific symptoms demand an immediate medical evaluation by an eye specialist or emergency room. The most concerning sign is the sudden onset of a large number of new floaters, described as a shower of specks, cobwebs, or a dark cloud, especially when accompanied by intense, continuous flashes of light. This combination strongly suggests a retinal tear or the beginning of a retinal detachment.
Another urgent warning sign is the appearance of a shadow, curtain, or veil that moves across or blocks part of the visual field. This symptom indicates that the retina has physically separated from its supporting tissue and requires immediate intervention to prevent permanent vision loss.
Flashes accompanied by severe, sudden headaches, confusion, slurred speech, or weakness on one side of the body may signal a stroke or TIA, necessitating a call to emergency services. Any abrupt change in vision, including sudden blurring or loss of peripheral sight, should prompt an immediate medical visit to protect sight.