A brown spot in the eye is medically known as a pigmented lesion, an accumulation of melanocytes, the cells responsible for producing melanin. These spots, similar to moles or freckles on the skin, can appear on the surface or deep inside the eye structure. While the presence of any new or changing spot may cause concern, the vast majority are harmless and are often discovered incidentally during a routine examination. Because a small percentage of these lesions can develop into a serious form of cancer, a professional ophthalmological evaluation is necessary to accurately determine the nature of the spot.
Common Benign Pigmentation
The most frequent type of brown spot found in the eye is called an ocular nevus, which is essentially a common freckle or mole. These nevi can be located on the conjunctiva, the transparent membrane covering the white of the eye, or on the iris, the colored part. Conjunctival nevi often appear yellow-brown, can slightly change in color or size over time, and are easily visible on the eye’s surface.
Another common location for these benign lesions is the choroid, a layer of blood vessels and connective tissue at the back of the eye, directly beneath the retina. These choroidal nevi are flat, slate-gray to light brown in color, and are typically only detected during a dilated eye exam. Choroidal nevi are present in approximately 5% to 10% of the adult population, making them the most common intraocular tumor. Like their skin counterparts, these pigmented spots are stable and pose no risk to vision or health.
Recognizing Changes That Require Medical Attention
Monitoring any brown spot requires recognizing specific changes that may signal a transformation toward malignancy. Eye specialists often use the adaptation of the ABCDE mnemonic, commonly used for skin cancer, to evaluate suspicious lesions. Asymmetry and Border irregularity are factors, where a benign spot typically maintains a uniform shape with clearly defined edges.
Color variation within the lesion, particularly the appearance of multiple shades of brown or black, can be a warning sign. A rapid increase in Diameter or Elevation, especially if the spot grows thicker than two millimeters, warrants immediate attention. New visual symptoms, such as flashes of light, an increase in floaters, or a sudden loss of vision, should be reported to an eye doctor immediately. Pain or redness associated with the pigmented area also requires evaluation.
Understanding Ocular Melanoma
Ocular melanoma, also known as uveal melanoma, is a rare form of cancer that arises from the melanocytes within the uvea, the middle layer of the eye. This layer includes the iris, the ciliary body, and the choroid, with the choroid being the most frequent site for this malignancy. Uveal melanoma is the most common primary eye cancer in adults, though its overall incidence is low, affecting about six people per million annually.
This type of cancer is dangerous because it can spread, or metastasize, to other parts of the body, most commonly the liver. Melanoma arising from the iris is usually noticed earlier due to its visible location and tends to be the least aggressive form. Tumors in the ciliary body are often discovered later because of their hidden location behind the iris, making them a more serious finding. Early detection of any suspicious growth is essential to improving patient outcomes and preventing metastatic disease.
How Doctors Diagnose and Monitor Eye Spots
The diagnostic process begins with a comprehensive, dilated eye examination using a slit lamp biomicroscope to inspect the spot’s surface characteristics. If the spot is on the back of the eye, a direct or indirect ophthalmoscope allows the doctor to view the internal structure of the eye. To accurately document the lesion’s size and appearance, fundus photography is performed, capturing high-resolution images for future comparison.
For spots located in the choroid, several specialized imaging techniques are used to gather more detail. Ocular ultrasound is employed to measure the lesion’s thickness and height, which is a factor in determining risk. Optical Coherence Tomography (OCT) provides a cross-sectional view, helping to detect subtle signs of fluid accumulation beneath the retina, known as subretinal fluid.
Based on these findings, a doctor will assign a risk profile to the nevus, often looking for the presence of orange pigment, which is a high-risk feature. Stable nevi that do not exhibit any high-risk features are typically placed on a monitoring schedule, such as follow-up examinations every six to twelve months. If the spot shows definite signs of growth or possesses multiple risk factors, the patient will be referred to an ocular oncologist for further evaluation and potential treatment.