A black spot on your eye usually falls into one of two categories: something you can see floating in your vision, or a visible dark mark on the surface of your eye that you (or someone else) noticed in the mirror. The cause and urgency depend entirely on which type you’re dealing with. Most of the time, these spots are harmless, but a few specific warning signs do warrant a prompt eye exam.
Spots in Your Vision vs. Spots on Your Eye
This distinction matters more than anything else. A spot that drifts when you move your eyes, settling slowly like a snowflake in water, is almost certainly a floater inside the eye. A spot that stays fixed in one place on the white or colored part of your eye, visible in a mirror, is a surface lesion. The two have completely different causes and different levels of concern.
Floaters move from second to second and come and go throughout the day, unlike a blind spot in your vision, which stays fixed in space. If you’re not sure what you’re dealing with, close one eye and look at a plain white wall or bright sky. Floaters will appear as small dark specks, threads, or cobwebs that shift when you try to look directly at them.
Floaters: The Most Common Cause
The vast majority of black spots people notice in their vision are floaters, and they’re a normal part of aging. Your eye is filled with a jelly-like substance called the vitreous, made mostly of water, collagen protein, and a carbohydrate called hyaluronan. When you’re young, this vitreous is a firm, clear gel. Over time, it gradually liquefies and contracts, pulling away from the inner surface of the eyeball.
As this happens, tiny clumps and strings of collagen form within the vitreous. These clumps block small amounts of light passing through your eye and cast shadows onto the retina at the back. Those shadows are what you perceive as floaters. Nearly everyone develops some floaters with age, and they’re usually more of a nuisance than a medical problem. You tend to notice them most against bright, uniform backgrounds.
A few new floaters appearing gradually over months or years is normal. What is not normal is a sudden burst of many new floaters, especially if accompanied by flashes of light or a shadow creeping across your field of vision like a curtain. These are warning signs of a retinal detachment, where the retina peels away from the back of the eye. Retinal detachment is a medical emergency that requires immediate treatment to prevent permanent vision loss.
Eye Freckles and Nevi
If the dark spot is something you can physically see on the surface of your eye, the most common explanation is a nevus, essentially a freckle. These are small colored growths that can appear on the white of the eye (conjunctiva), on the iris (the colored ring), or deeper inside the eye where only a doctor would spot them. They range in color from yellow to gray to brown, and many people have had them since childhood without ever noticing.
An iris nevus sits within the layers of the iris and is typically flat and stable. In rare cases, a larger nevus can extend deeper into the iris tissue. Benign nevi don’t cause symptoms, don’t affect your vision, and don’t require treatment. Your eye doctor will likely photograph the spot and measure it so they can track it over time, since the main concern with any pigmented spot is making sure it isn’t growing.
Primary Acquired Melanosis
A flat, brown patch that appears on the white of your eye during adulthood, rather than being present since childhood, may be primary acquired melanosis (PAM). This looks like a patch of brown pigmentation on the conjunctiva, at least a millimeter across, and it tends to be irregular in shape. PAM itself isn’t cancer, but some forms carry a small risk of progressing to melanoma over time.
The risk depends on the cellular characteristics of the patch, which can only be determined through a biopsy. PAM without abnormal cells shows a 0% progression rate to melanoma. PAM with mildly abnormal cells also shows 0% progression. PAM with severely abnormal cells progresses to melanoma in about 13% of cases. The larger the area of PAM, measured in clock hours around the eye, the greater the risk. Because of this, eye doctors monitor these patches carefully and may biopsy them to determine the level of concern.
Corneal Foreign Bodies
A dark spot on the clear front surface of your eye (the cornea) can sometimes be a tiny embedded foreign body. This is especially common if you work with metal, grind materials, or were recently in a windy, dusty environment. Metallic particles are particularly problematic because iron-containing fragments deposit rust onto the cornea, creating a visible brownish or dark ring. You’ll usually know something is wrong because the eye feels irritated, watery, or painful, particularly when blinking.
Even a microscopic metal shard can appear as a dark or reflective spot and cause ongoing damage through oxidative reactions in the corneal tissue. If you suspect something is stuck in your eye, avoid rubbing it. This type of spot needs professional removal, as leaving a metallic foreign body in place can lead to infection and scarring.
Ocular Melanoma
The concern most people have when they search this question is cancer, so it’s worth putting the risk in perspective. Uveal melanoma, the most common primary eye cancer in adults, occurs in roughly 4 to 6 people per million each year. Conjunctival melanoma is even rarer, at about 0.2 to 0.8 cases per million annually. These are genuinely uncommon cancers.
That said, any pigmented spot on the eye that is growing, changing color, or accompanied by vision changes should be evaluated. Eye doctors use several tools to distinguish a benign nevus from something more concerning. A slit-lamp exam provides a magnified view of the surface. Optical coherence tomography (OCT) creates cross-sectional images that reveal how deep a lesion extends, whether the tissue layers look normal, and whether there are subtle changes invisible to the naked eye. Ultrasound can measure the thickness of deeper lesions. For spots inside the eye, doctors watch for features like thickness greater than 2 mm, fluid accumulating beneath the retina, and the spot exceeding 5 mm in diameter.
What to Do Next
If you’ve noticed a handful of floaters that appeared gradually and don’t interfere with your vision, you’re likely experiencing a normal age-related change. No treatment is needed, though mentioning them at your next eye exam is reasonable.
Schedule a prompt eye exam if you notice a new dark spot on the visible surface of your eye that you haven’t seen before, or if a known spot seems to be changing in size or color. A pigmented lesion on the white of the eye that appeared in adulthood deserves evaluation even if it isn’t bothering you.
Go to an eye doctor or emergency room immediately if you experience a sudden shower of new floaters, flashes of light in one or both eyes, or a dark shadow or curtain encroaching on any part of your field of vision. These symptoms suggest a possible retinal detachment, and outcomes are significantly better with early treatment.