Seeing colors, lights, or patterns that do not exist in the external environment often causes concern. These visual symptoms, broadly termed photopsias, can range from simple flashes of light to complex geometric shapes. Understanding whether the source is the eye, the optic nerve, or the visual processing centers in the brain is the first step toward addressing the symptom. This article explores the various reasons why you might perceive these visual disturbances, differentiating between temporary occurrences and those that require urgent medical attention.
Temporary Visual Phenomena
The most common reasons for perceiving light or color without an external source are often harmless, resulting from mechanical stimulation of the retina. This mechanical activation tricks the brain into perceiving light, a phenomenon known as phosphenes, or “seeing stars.” Phosphenes can be generated by rubbing your eyes firmly, as the pressure physically stimulates the light-sensitive cells. Forceful actions like a hard sneeze, a deep cough, or a sudden blow to the head can also momentarily jar the eye or increase internal pressure, leading to a quick, isolated flash of light.
Other temporary events relate to rapid changes in blood flow, such as standing up too quickly. A sudden drop in blood pressure can cause a transient reduction in blood flow to the visual cortex or the retina. This leads to a momentary perception of colors or a graying out of vision. These visual anomalies are brief, lasting only a few seconds, and resolve as soon as normal blood flow stabilizes.
Visual Disturbances Linked to Migraine Aura
Visual symptoms related to a migraine aura involve complex, organized patterns originating in the brain, not the eye itself. The most recognizable form is the scintillating scotoma, characterized by a shimmering, expanding blind spot. This typically features zigzagging lines or a fortified castle-like pattern. These patterns can be multicolored or silvery and usually expand outward across the visual field over 20 to 30 minutes.
The underlying cause is a neurological event called Cortical Spreading Depression (CSD). This is a slow, propagating wave of hyperactivity followed by inhibition that moves across the visual cortex in the back of the brain. The visual cortex misinterprets this electrical wave as a visual input, which explains why the disturbance appears to move or expand gradually.
A visual aura can occur without a subsequent headache, known as an acephalgic or “silent” migraine. In these cases, the person experiences only the complex visual display, sometimes accompanied by sensory disturbances like tingling or numbness. Since the visual cortex processes information from both eyes, these patterns usually affect vision in both eyes simultaneously, differentiating them from eye-specific problems.
Internal Eye Changes and Retinal Health
Flashes of light and new floaters that appear suddenly signal changes within the eye, specifically involving the vitreous humor and the retina. The vitreous is a clear, gel-like substance that fills the eye’s main cavity and is attached to the retina. As a person ages, this gel naturally shrinks and liquefies, leading to Posterior Vitreous Detachment (PVD).
When the vitreous gel separates from the retina, it can tug on the light-sensitive tissue at points of firm attachment. Since the retina’s only function is to send visual signals to the brain, any mechanical stimulation is perceived as light. This is often described as a streak of lightning or a camera flash in the peripheral vision.
While PVD is a common and usually benign age-related process, the traction can sometimes be strong enough to cause a retinal tear. Fluid can pass through this tear and accumulate behind the retina, causing it to peel away from the underlying tissue. This condition, known as retinal detachment, is a medical emergency that can lead to permanent vision loss if not treated promptly.
Signs of an urgent problem include:
- A sudden increase in the number of flashes.
- A dense shower of new floaters.
- The appearance of a dark shadow or a “curtain” moving across the field of vision.
Any acute onset of these symptoms requires an immediate, dilated eye examination to check for a retinal tear or detachment. If no tear is present, the flashes typically decrease over days to weeks as the vitreous completely separates and the traction ceases.
Systemic and Medication-Induced Causes
Visual disturbances, including seeing colors or halos, can be side effects of systemic health conditions or certain medications. Some prescription drugs interfere with chemical processes in the retina or blood flow to the optic nerve, leading to changes in color perception. For example, certain erectile dysfunction medications can temporarily inhibit retinal enzymes, sometimes resulting in blue-tinged vision.
Drugs used for cardiac conditions, such as the anti-arrhythmic amiodarone, or high-dose antibiotics can affect the optic nerve or retina, potentially causing color vision changes or scotomas. Certain blood pressure drugs, particularly vasodilators or vasoconstrictors, can also cause shimmering or halo effects around lights by altering blood flow dynamics near the visual pathway.
Systemic diseases like uncontrolled diabetes can lead to diabetic retinopathy, where damaged blood vessels in the retina cause bleeding or fluid leakage, leading to visual distortions. Sudden, profound visual changes, including abrupt vision loss or the onset of flashes, can also signal a neurological event like a Transient Ischemic Attack (TIA) or stroke. This is especially true if accompanied by weakness, numbness, or difficulty speaking. Any new, persistent, or dramatic change in vision should be evaluated by a healthcare professional.