It is common to perceive white flashes or patterns of light even when your eyes are closed. This phenomenon, often called “seeing stars,” is usually a normal function of your visual system. While typically harmless, these sensations can sometimes signal an underlying medical condition. Understanding the various causes helps differentiate between typical occurrences and those requiring medical evaluation.
Understanding Phosphenes
The technical term for light sensations perceived without an external light source is phosphenes. They can appear as flashes, dots, lines, or geometric patterns. Phosphenes arise from stimulation of the retina, the light-sensitive tissue at the back of your eye, or the visual cortex in your brain.
Mechanical stimulation is a common cause. Applying pressure to a closed eyelid, such as by rubbing your eyes, directly stimulates retinal photoreceptor cells, leading to the perception of light. Rapid changes in light levels, like moving from a bright to a dark room, can also trigger phosphenes as your eyes adapt, as the retina’s sensitivity adjusts. Spontaneous neural activity within the retina or visual cortex can also generate phosphenes; cells in your visual system can fire randomly even without external stimuli.
Medical Conditions Causing Flashes
While many instances of flashes are benign, they can sometimes be a symptom of underlying medical conditions. These conditions often involve changes within the eye itself, particularly affecting the vitreous humor or the retina.
Ocular migraine, also known as a retinal migraine, can cause temporary visual disturbances in one eye. These may include shimmering or twinkling lights, zigzag patterns, or even blind spots, and typically last between 5 to 60 minutes. Posterior vitreous detachment (PVD) is another common cause, especially as people age. The vitreous is a gel-like substance filling the eye, and as it liquefies and shrinks, it can pull away from the retina. This pulling can stimulate the retina, resulting in flashes of light, often described as lightning streaks or camera flashes, and may be accompanied by new floaters.
Retinal detachment, where the retina separates from its underlying support tissue, is a medical emergency that can lead to permanent vision loss if not addressed promptly. Symptoms include sudden flashes of light, a significant increase in new floaters, and a shadow or “curtain” appearing in your vision. Other less common causes of flashes can include eye trauma, inflammation within the eye, or in rare cases, certain neurological conditions.
When to Consult a Doctor
It is important to recognize when flashes of light may signal a more serious issue that requires immediate medical attention. While occasional, isolated flashes are often harmless, certain accompanying symptoms warrant prompt evaluation by an eye care professional.
You should seek immediate medical attention if you experience a sudden increase in the number or intensity of flashes. If new floaters, such as specks, threads, or cobweb-like shapes, appear at the same time, this is concerning. A shadow or “curtain” appearing in your vision can indicate retinal detachment. Any flashes accompanied by eye pain or a significant decline in overall vision should also prompt an urgent visit to an ophthalmologist.
Diagnosis and Management
When you consult a doctor for flashes of light, a comprehensive eye examination is typically performed. This examination includes dilating your pupils with eye drops to allow the ophthalmologist to inspect the retina and vitreous. This dilated fundus exam helps identify any tears, detachments, or other abnormalities.
Depending on the findings, additional specialized tests, such as an ultrasound of the eye, may be ordered if the cause is not visible during the initial exam. For benign conditions like posterior vitreous detachment without complications, observation is often sufficient, as the flashes usually subside over weeks or months. However, if a retinal tear is diagnosed, immediate treatment such as laser photocoagulation or cryotherapy can be performed to seal the tear and prevent retinal detachment. If a retinal detachment is present, surgical intervention is required to reattach the retina and preserve vision.