Seeing colored spots, particularly purple, can be alarming. This phenomenon is a positive visual disturbance, where you perceive light or color not actually present externally. While many causes are temporary, any sudden, persistent, or worsening change requires immediate consultation with an eye care professional. This article explores reasons behind seeing purple spots, ranging from simple mechanical stimulation to serious ocular and systemic conditions.
Understanding Phosphenes and Scotomas
The visual spots or flashes you perceive can generally be categorized into two phenomena: phosphenes and scotomas. Phosphenes are light sensations generated by the non-light-based stimulation of the retina or visual pathway, creating the illusion of light. These are often described as flashes, sparkles, or unstructured patterns of color, which can include the color purple.
A scotoma, in contrast, is an area of partial or complete vision loss, appearing as an obscured spot within your visual field. When a disturbance appears purple or violet, it often relates to how the nerve cells in your retina or brain are being excited. For instance, mechanical pressure on the eye can stimulate photoreceptors to fire, sometimes resulting in a purple or violet hue. The specific appearance—whether a momentary flash (phosphene) or a persistent blind spot (scotoma)—helps determine the underlying cause.
Transient Causes Related to Brain Activity and Pressure
One of the most common causes of temporary, colored visual disturbances is the visual aura associated with migraine headaches. This aura originates in the brain’s visual processing center, the occipital cortex, and is not an issue with the eye itself. The mechanism is a slow-moving wave of electrochemical change known as Cortical Spreading Depression (CSD).
As the CSD wave propagates across the cortex, it causes a temporary disruption in nerve activity that is perceived as visual symptoms, often lasting between five and sixty minutes. These symptoms frequently begin as a small, shimmering spot that expands into a zigzag pattern of light, sometimes described as a scintillating scotoma. The colors, which can include purple, are positive visual hallucinations that occur before, or sometimes without, the onset of the migraine headache.
Other transient visual spots are related to temporary changes in blood flow or physical pressure. Orthostatic hypotension, a temporary drop in blood pressure upon standing up quickly, can briefly reduce blood flow to the brain and retina, causing temporary “graying out” or seeing spots. Similarly, intense straining, such as from a strong cough or heavy lifting, can cause phosphenes. This physical pressure causes the vitreous gel inside the eye to briefly tug on the retina, which the brain interprets as a flash of light.
Ocular Conditions Requiring Urgent Evaluation
Flashes or spots that are new, sudden, or increasing in frequency can signal a physical problem within the eye that requires immediate attention from an ophthalmologist. One serious concern is a retinal tear or detachment, where the light-sensitive tissue at the back of the eye pulls away from its underlying support layer.
The perception of flashes in these cases is known as photopsia, which occurs because the vitreous gel pulls on the retina, mechanically stimulating the photoreceptor cells. If a tear progresses to a detachment, the resulting loss of blood supply to the affected area causes a shadow or a dark “curtain” to move across the field of vision, which is a significant scotoma.
A more common, age-related event is Posterior Vitreous Detachment (PVD), where the vitreous naturally shrinks and separates from the retina. This separation process often causes new floaters and flashes as the gel tugs on the retina, but it is not a tear itself. However, because PVD can sometimes cause a retinal tear, any sudden onset of flashes or floaters must be examined promptly to ensure the retina is intact.
Another condition that affects color perception is optic neuritis, which involves inflammation and swelling of the optic nerve. This inflammation can cause diminished vision, pain with eye movement, and difficulty perceiving colors. Patients often report that colors, particularly red hues, appear “washed out” or desaturated, a disturbance that may contribute to the perception of unusual or muted colors, including purple.
Systemic Health Factors Affecting Vision
Visual disturbances can also be a symptom of conditions originating elsewhere in the body, primarily those affecting the vascular or neurological systems. Hypertensive retinopathy occurs when chronic or acutely severe high blood pressure damages the fine blood vessels supplying the retina. This can lead to small hemorrhages, fluid leakage, and areas of restricted blood flow.
The damage manifests as spots or floaters caused by blood or fluid deposits, such as cotton-wool spots, which are small, white areas of nerve fiber damage. In cases of hypertensive crisis, the pressure can cause rapid and severe damage, including swelling of the optic nerve, which constitutes a medical emergency.
Visual changes can also signal a neurological event, such as a Transient Ischemic Attack (TIA) or stroke, which result from reduced blood flow to the brain’s visual processing centers. Reduced circulation to the back of the brain can cause bilateral photopsia, often described as jagged flashes that last a few minutes.
Diabetes-related retinopathy, stemming from high blood sugar damaging retinal blood vessels, is another systemic cause of visual spots. Damaged vessels can leak fluid or blood into the vitreous, which is perceived as floaters or dark spots in the vision. Furthermore, diabetic retinopathy is a risk factor for developing tractional retinal detachment, where scar tissue pulls the retina away from the back of the eye.