The white of the eye is technically known as the sclera, a dense, protective layer of connective tissue that gives the eyeball its structure. This layer is covered by the conjunctiva, a thin, clear membrane that contains small blood vessels and pigment-producing cells. While the sclera is typically white, brown or gray discoloration can be concerning. Pigmentation can arise from many factors, ranging from common, localized deposits of melanin to signs of internal metabolic conditions.
Benign Pigmentation (Common Causes)
The most frequent causes of brown spots relate to the natural production and accumulation of melanin. These spots are usually harmless and require only routine monitoring. Scleral nevi, often called “eye freckles,” are common, localized clusters of melanocytes that appear as flat, brownish spots. Similar to moles on the skin, these are typically present from birth or develop in early childhood and do not pose a health concern.
Racial melanosis, sometimes called complexion-associated melanosis, is highly prevalent in individuals with naturally darker skin tones. This physiological pigmentation appears as flat, patchy brown or slate-gray areas on the conjunctiva, often near the limbus (the border where the sclera meets the cornea). Racial melanosis usually affects both eyes and remains stable throughout life.
The benign growth known as a pinguecula is typically yellowish, but chronic irritation or severe sun exposure can cause it to develop a brownish hue. A pinguecula is a deposit of protein, fat, or calcium that forms on the conjunctiva, most often on the side closest to the nose.
Discoloration Linked to Systemic Health Issues
When pigmentation is not a simple localized freckle, it may indicate underlying metabolic or hormonal irregularities. A rare genetic disorder called Alkaptonuria leads to the accumulation of homogentisic acid in connective tissues, causing Ochronosis. This metabolic buildup results in characteristic blue-black or brown-gray deposits in the sclera, often seen near the insertion points of the eye muscles. These pigment spots can appear symmetrically in both eyes and are often one of the earliest signs of the disorder, preceding joint and cartilage issues.
Hormonal imbalances, such as those occurring in Addison’s disease, can also cause pigmentation changes on the sclera and other mucous membranes. Addison’s disease involves insufficient production of adrenal hormones, which prompts the pituitary gland to increase the release of Adrenocorticotropic hormone (ACTH). Since ACTH shares a precursor molecule with melanocyte-stimulating hormone, this elevated level leads to increased melanin production throughout the body, resulting in diffuse brownish hyperpigmentation.
Certain medications are known to induce pigment deposits in the eyes. Minocycline, a long-term tetracycline derivative antibiotic, is a notable example. Long-term use of this drug can cause a slate-gray or bluish-black discoloration of the sclera and conjunctiva, typically appearing as a band near the limbus. The pigmentation is related to the drug’s lipophilic properties, allowing it to accumulate in tissues, and while usually harmless, the discoloration can sometimes be permanent even after stopping the medication.
Pigmentation Associated with Ocular Disease
Some forms of brown discoloration are directly related to specific conditions on the eye’s surface or within the eye structure. Primary Acquired Melanosis (PAM) develops in adulthood, typically presenting as a flat, patchy brown lesion on the conjunctiva of a single eye. PAM is classified based on the presence of atypia (abnormal cell changes); PAM without atypia is considered benign. PAM with atypia, however, carries a risk of progression to conjunctival melanoma, making careful monitoring essential.
Conjunctival melanoma is a rare but serious form of eye cancer that can arise from a pre-existing nevus or from PAM. Warning signs of a potentially malignant lesion include rapid growth, a raised or nodular appearance, or the development of prominent blood vessels around the spot. Nevus of Ota involves deep, blue-brown pigmentation that affects the skin around the eye and the sclera, often on one side of the face. This condition results from an accumulation of melanocytes deep within the tissues and indicates an increased lifetime risk for developing uveal melanoma and glaucoma.
When to Seek Professional Evaluation
Any new or changing pigmentation on the white of the eye warrants evaluation by an eye care professional. A sudden appearance of a brown spot, or any change in an existing spot, should prompt an appointment to establish a baseline diagnosis. Specific changes that necessitate prompt evaluation include an increase in size, a change in shape or color, or if the spot becomes raised or nodular.
It is important to seek professional advice if the discoloration is accompanied by other symptoms, such as pain, vision changes, or the appearance of new, prominent blood vessels near the area. An eye doctor uses specialized tools, like a slit lamp biomicroscope, to examine the depth and characteristics of the pigment. This detailed examination helps determine whether the pigment is a harmless accumulation of melanin or a sign of a more complex ocular or systemic condition.