Seeing a green spot in your vision can be startling, but this experience, known as photopsia, is a common type of visual disturbance. The perception of colored spots or flashes indicates a temporary disruption in how light is detected by the retina or how those signals are processed by the brain. While often a harmless, brief event, a green spot can occasionally signal a change in ocular health that warrants professional attention.
Transient and Common Explanations
The most frequent cause of a temporary green spot is a negative afterimage, a phenomenon rooted in photoreceptor fatigue. When the eye stares intently at a brightly colored object, the cone cells responsible for detecting that specific hue become temporarily overstimulated. If you look at a red object for an extended period, those cones tire out, causing the visual system to compensate when you look away at a neutral surface. The resulting afterimage appears in the complementary color, which, for red, is green.
Moving quickly between extreme light conditions can also induce a short-lived visual artifact. Stepping from a dark room into bright sunlight can momentarily overwhelm the visual pigments in the retina. Another harmless cause involves mechanical stimulation of the eyeball, which generates light sensations called phosphenes. Rubbing your eyes applies pressure that excites the photoreceptor cells, leading to brief flashes or spots of light that can sometimes be perceived as having a colored tint.
Ocular Causes of Colored Visual Disturbances
More persistent or recurring spots may be related to the physical structure inside the eye, specifically the vitreous humor and the retina. The vitreous is a gel-like substance that fills the eye and is normally attached to the retina, the light-sensitive tissue at the back of the eye. As a person ages, the vitreous naturally shrinks and liquefies, which can lead to a posterior vitreous detachment.
This detachment is typically harmless, but as the gel pulls away, it can tug on the delicate retinal tissue. This mechanical stimulation causes the retinal cells to fire electrical impulses, which the brain interprets as flashes of light, or photopsia. These flashes are often white or clear streaks, but they can also manifest as colored lights, including green or yellow-green, especially in the peripheral vision. A sudden increase in these spots or flashes, particularly when accompanied by a veil or shadow over the vision, may indicate a retinal tear or detachment, requiring immediate medical evaluation.
Systemic and Neurological Triggers
Visual spots and other disturbances can also originate outside the eye, often within the nervous system. A common neurological cause is a migraine aura, which is a wave of altered electrical activity that spreads across the visual cortex of the brain. The disturbance typically appears as a scintillating scotoma, a growing blind spot with a shimmering, zigzagging border that can be colorless or brightly colored.
Circulatory issues can also affect visual processing due to a temporary reduction in blood flow or oxygen supply. For example, a sudden drop in blood pressure (orthostatic hypotension) may cause a transient visual darkening or the appearance of spots. Furthermore, some prescription medications list visual disturbances as a side effect, including temporary changes in color perception or distortions.
Identifying Serious Symptoms and Seeking Care
While most instances of seeing a green spot are benign, certain accompanying symptoms necessitate prompt medical attention. Any sudden onset of new, persistent, or dramatically increasing light flashes or spots should be evaluated by an eye care professional immediately, especially if confined to one eye.
A sudden shadow, curtain, or veil moving across any part of your visual field is a particularly concerning sign that may indicate a retinal detachment. Additional symptoms like severe head pain, nausea, or a loss of peripheral vision alongside the spots require urgent consultation. If you notice persistent visual changes after starting a new medication, consulting the prescribing physician or a pharmacist is also advisable.