Brown spots appearing in or on the eye are fundamentally an accumulation of pigment, most often melanin, the same substance that colors hair and skin. These spots are common and typically harmless, similar to a mole or freckle found elsewhere on the body. The significance of the spot depends entirely on its location within the eye’s structure. A brown spot on the colored part of the eye has a different cause than one on the clear surface or the white backdrop. Understanding the specific anatomy where the spot lies is the first step in determining whether it is benign or requires attention from an eye care professional.
Brown Spots on the Iris
The iris, the colored diaphragm of the eye, can develop various pigmented lesions, most stemming from a clustering of melanocytes. The smallest and most common are iris freckles, which appear as tiny, flat, dark brown flecks resting superficially on the iris surface. These freckles are a simple buildup of melanin pigment and are considered benign, not requiring routine follow-up.
Iris nevi are similar to freckles but are larger and penetrate deeper into the iris tissue layer called the stroma. Like a mole on the skin, an iris nevus is a benign growth that is monitored over time due to a small risk of malignant transformation.
A rare cause of yellowish-brown spots is the presence of Lisch nodules, which are small, dome-shaped growths seen in individuals with Neurofibromatosis Type 1 (NF1). These nodules are harmless and rarely cause vision problems, but their presence is a strong diagnostic sign for the underlying systemic condition. The most serious, though uncommon, cause is iris melanoma, a malignant tumor that usually appears as a thicker, growing lesion that may cause secondary issues like glaucoma.
Brown Spots on the Conjunctiva and Sclera
Spots on the outer surface of the eye are found either on the sclera (the white part) or the conjunctiva (the thin, clear membrane covering it). The most frequent finding is a conjunctival nevus, a mole-like spot that ranges in color from yellow to dark brown. These nevi are usually present from birth or develop in childhood and may increase pigmentation during hormonal changes like puberty or pregnancy.
Racial melanosis, common in people with darker complexions, appears as flat, symmetrical, benign patches of pigmentation on the conjunctiva, often around the edges of the cornea. A more concerning development is Primary Acquired Melanosis (PAM), typically a unilateral, patchy, flat area found in older, fair-skinned individuals. PAM is important because it is considered a precursor lesion that can progress into conjunctival melanoma, necessitating careful monitoring. Residue from a healed subconjunctival hemorrhage or a retained foreign body can also leave a temporary or permanent brown or rust-colored stain on the surface tissues.
Corneal Deposits and Rings
Brown spots on the cornea, the clear dome over the iris, are often chemically based deposits rather than melanin pigmentation. One common example is the Hudson-Stähli line, a thin, horizontal brown line representing iron deposition in the corneal epithelium. This line is seen in people over the age of 50 and is a benign finding related to the pooling and movement of the tear film.
Other iron accumulation lines include the Fleischer ring, a ring of iron pigment that forms at the base of the cone-shaped protrusion of the cornea in keratoconus. Iron deposits can also form a rust ring, a dark spot left behind after a metallic foreign body has been removed from the corneal surface. A Kayser-Fleischer ring is a distinct circular deposit of copper in the outermost layer of the cornea. This olive green to brown ring is highly suggestive of Wilson’s disease, a rare systemic disorder that causes copper to accumulate in the body.
When a Spot Requires Medical Evaluation
The most important factor in assessing any brown spot on the eye is change over time, regardless of its location. Any lesion that is new, rapidly growing, or changing color should be evaluated by an eye care professional.
Signs of a suspicious lesion can be remembered using adapted criteria similar to the skin cancer “ABCDE” rule.
Signs of Suspicious Lesions
- Asymmetry, where one half of the spot does not match the other.
- Border irregularity, where the edges are ragged or poorly defined.
- Color variation, such as multiple shades of brown, black, or red within the spot.
- Diameter, typically greater than two millimeters on the iris.
- Evolving lesions that change in size, shape, or elevation.
Any spot that causes new symptoms like pain, blurred vision, or flashes of light, or a conjunctival lesion that appears to cross onto the clear cornea, warrants an urgent examination.