Seeing spots or flashes of color in your vision can be unsettling, often prompting concern about eye health. These visual disturbances, ranging from subtle specks to dramatic patterns, result from various phenomena occurring within the eye or the brain. Understanding the nature of these visual events is the first step toward determining their cause, which may be harmless or signal a condition requiring medical evaluation.
Classifying the Types of Visual Spots
The underlying cause of a visual disturbance depends heavily on the specific way it manifests in your vision. These phenomena are grouped into distinct categories based on their appearance and origin.
The most common visual spots are floaters, which appear as semi-transparent specks, threads, or cobwebs that drift slowly across your field of view. These are not external objects but rather shadows cast onto the retina by tiny clumps of debris suspended within the clear, jelly-like substance filling the eyeball, known as the vitreous humor. Floaters tend to become more noticeable when looking at a plain, bright background, such as a blue sky or a white wall.
Another distinct experience is flashes, medically termed photopsia, which are brief arcs or streaks of light often appearing in peripheral vision. Flashes occur when the retina, the light-sensitive tissue lining the back of the eye, is mechanically stimulated. The brain interprets this mechanical stimulation as light, even though no actual light source is present.
Temporary spots seen immediately after looking at a bright light source are called afterimages. This phenomenon is a normal physiological response where the photoreceptor cells in the retina are temporarily overstimulated or “bleached” by intense light. Separately, some people experience shimmering, geometric, or zigzagging light patterns, often referred to as a visual aura, which typically originates from activity in the brain rather than the eye itself.
Temporary and Common Explanations
Many instances of seeing light or color are fleeting and result from harmless physical or physiological events. These temporary visual effects, often called phosphenes, occur when the visual system is activated by a stimulus other than light.
One frequent cause is applying physical pressure to the eye, such as rubbing your eyelids forcefully. This action mechanically stimulates the retina, causing a burst of light or colored spots that briefly appear even when the eyes are closed. Phosphenes can also be triggered by sudden increases in eye pressure from events like sneezing, heavy coughing, or strenuous activity.
A transient drop in blood pressure, such as when standing up quickly, can also cause temporary spots or “seeing stars.” This phenomenon, known as orthostatic hypotension, leads to a momentary reduction of blood flow and oxygen to the brain and retina. The resulting lack of oxygen, or hypoxia, can cause the visual neurons to misfire, creating a brief visual disturbance that resolves once blood flow normalizes. Additionally, afterimages are a common experience, lasting only seconds or minutes as the retinal cells recover their sensitivity after intense light exposure.
Underlying Ocular Conditions
When visual spots or floaters persist or become a regular occurrence, they are often linked to structural changes within the eye, particularly in the vitreous humor. The vitreous is a gel-like substance composed mostly of water and fine collagen fibers. With age, this gel begins to liquefy, a process called syneresis, causing the collagen fibers to clump together.
These collagen clumps cast distinct shadows onto the retina, which are perceived as age-related floaters. This structural change is a normal part of the aging process and is usually benign. Over time, the shrinking vitreous gel may separate from the retina at the back of the eye, a common event called Posterior Vitreous Detachment (PVD).
PVD frequently causes a sudden onset of new, larger floaters, sometimes described as a large ring or cobweb. Flashes may also occur during PVD as the separating vitreous tugs on the retina, which interprets the mechanical force as light. While PVD is generally not sight-threatening, the initial tugging phase can sometimes cause complications, necessitating an eye examination to ensure the retina remains intact.
Changes in the eye’s internal environment due to systemic diseases can also cause floaters. For example, in advanced stages of diabetic retinopathy, damaged blood vessels in the retina can leak blood into the vitreous gel. This blood appears as a sudden shower of new floaters, signaling an underlying condition that requires specialized management.
When Colored Spots Signal an Emergency
While most visual spots are harmless, a sudden change in their appearance or frequency can signal an acute medical emergency requiring immediate attention. The most serious concern arises when the separating vitreous gel pulls hard enough to create a tear in the retina. A retinal tear allows fluid to pass beneath the retina, causing it to lift away from the underlying tissue in a condition known as retinal detachment.
The warning signs of a retinal tear or detachment are distinct and severe. They often present as a sudden, dramatic increase in the number of floaters, sometimes described as a “shower” of black specks. This is frequently accompanied by a sudden increase in flashes of light, especially in the peripheral vision. As the retina detaches, a shadow or a “curtain” may descend or ascend across the field of vision, representing the area of the retina that has lost its blood supply and function.
Vascular Events
A different type of urgent visual event is related to the brain’s blood supply, such as the temporary vision loss known as amaurosis fugax. This condition, often described as a shade or curtain descending over vision in one eye, is caused by a temporary disruption of blood flow to the retina or optic nerve. Amaurosis fugax is a significant warning sign because it can indicate an underlying transient ischemic attack (TIA) or stroke risk, often due to plaque or a blood clot traveling from the carotid artery.
Migraine Aura and Systemic Symptoms
Visual disturbances related to migraines, often termed migraine with aura, are typically a neurological event affecting both eyes, characterized by shimmering, geometric patterns that usually resolve within 60 minutes. However, if any visual change is accompanied by severe headache, weakness, numbness, or difficulty speaking, it could indicate a serious vascular event. Any sudden onset of visual disturbances, especially those involving a curtain effect, pain, or significant vision loss, requires an immediate eye examination to prevent permanent vision damage.