The common experience of “seeing stars” is medically known as photopsia, a visual disturbance where a person perceives flashes, sparks, or streaks of light that do not correspond to any actual light source. This sensation occurs when the visual system, including the retina or the brain’s visual cortex, is stimulated by something other than visible light. The brain interprets these artificial signals as light because the nerve pathway transmitting visual information has been activated.
Temporary Causes Related to Blood Flow and Impact
The most frequent causes of photopsia are brief and harmless, often resulting from mechanical pressure or a temporary lack of oxygen reaching the eye and brain. A sudden blow to the head, such as an impact, causes immediate photopsia because the mechanical force jostles the retina. This physical stimulation causes light-sensing cells to fire electrical impulses, which the brain processes as a brief burst of light.
Orthostatic hypotension, a rapid drop in blood pressure when standing up too quickly, is another common cause. This swift change causes a temporary reduction in blood flow, leading to a momentary lack of oxygen and nutrients in the brain and eyes. The resulting low oxygen state, or ischemia, can trigger the visual disturbance. Dehydration and excessive heat contribute by lowering overall blood volume.
Low blood sugar, or hypoglycemia, is a systemic condition that can temporarily lead to visual disturbances. The retina has high metabolic demands and is sensitive to glucose fluctuations, especially in individuals with diabetes. Acute drops in blood glucose can affect retinal function, potentially causing symptoms like blurred vision or flashes of light until normal sugar levels are restored.
Visual Disturbances Stemming from the Eye and Brain
Photopsia can be a symptom of conditions related to the eye’s structure or the brain’s neurological function. A common internal cause is a migraine aura, sometimes called an ocular migraine, which is a visual disturbance occurring with or without a headache. These phenomena are perceived in both eyes and often appear as shimmering, zigzagging lines or a blind spot that resolves over 10 to 30 minutes.
Vitreous detachment or traction originates in the eye itself. The vitreous is a clear, gel-like substance filling the eyeball that naturally shrinks and liquefies with age. If the shrinking vitreous pulls on the retina, this mechanical tugging stimulates photoreceptor cells. This leads to the perception of flashes, often described as lightning streaks or camera flashes in the peripheral vision.
Underlying health issues like high blood pressure (hypertension) can indirectly contribute to visual symptoms. Uncontrolled hypertension can damage the delicate blood vessels supplying the retina, leading to changes in blood flow and visual field issues. Reduced blood flow to the back of the brain, known as vertebrobasilar insufficiency, can also cause brief, bilateral flashes of light due to temporary ischemia.
When Seeing Stars Signals an Emergency
While many instances of photopsia are benign, a sudden onset of specific symptoms alongside flashing lights requires immediate medical attention. The most urgent concern is a retinal tear or detachment, where the retina separates from the underlying tissue. Symptoms include a sudden increase in floaters (dark spots or lines in the vision) accompanied by persistent flashes of light.
A distinct red flag is the perception of a shadow, curtain, or veil moving across the field of vision, signaling that a portion of the retina has detached. Since the retina does not contain pain receptors, a tear or detachment is painless, making the visual signs the sole warning. Swift treatment is necessary to prevent permanent vision loss.
Seeing stars paired with neurological symptoms may signal a serious medical event like a stroke or transient ischemic attack (TIA). These symptoms include a severe, sudden headache, confusion, weakness on one side of the body, or difficulty speaking. Visual flashes that are hyperacute and maximal at onset, especially when combined with these neurological changes, require an immediate trip to the emergency room.