Just like skin, the eyes can also develop pigmented spots. This common phenomenon, often called an “eye freckle,” is medically known as an ocular nevus (plural: nevi). These spots are essentially benign collections of pigment-producing cells called melanocytes, the same cells responsible for moles and freckles elsewhere on the body. While most are harmless, an ocular nevus can sometimes change over time, which introduces a small risk of malignant transformation. Regular monitoring is generally recommended because, like a skin mole, an eye nevus has the potential to develop into a type of cancer called ocular melanoma.
Understanding Ocular Nevi and Their Locations
The term ocular nevus is a broad category, and the spot’s location within the eye determines its visibility and the specific monitoring approach. These nevi are generally classified into three main types based on where the melanocytes have clumped together. Iris nevi are among the most visible, appearing as small, dark brown flecks or spots on the colored part of the eye. They are common and rarely develop into melanoma, but their presence is a reason for routine observation.
Conjunctival nevi are found on the clear, thin membrane that covers the white part of the eyeball, the sclera, and the inside of the eyelids. These spots often look like typical skin freckles and can range in color from yellow to brown, sometimes changing in shade over time. While usually benign, their location on the eye’s outer surface makes them easier to monitor for changes in size or appearance.
The third type, the choroidal nevus, is located in the choroid, a layer of blood vessels and tissue beneath the retina at the back of the eye. This location means they are completely invisible to the naked eye and can only be detected during a comprehensive, dilated eye examination. Choroidal nevi are the most common type found inside the eye, and their hidden position makes professional monitoring particularly important.
When a Freckle Becomes a Concern
A benign ocular nevus becomes a health concern if it shows signs of transforming into ocular melanoma, the most common primary eye cancer in adults. This transformation is rare, but the risk is highest with choroidal nevi due to their location and the difficulty in self-monitoring. Ophthalmologists use specific risk factors to determine which nevi require closer attention, especially those in the choroid.
The risk factors for a choroidal nevus changing into a small melanoma are often summarized by the mnemonic “TFSOM-DIM,” which guides clinicians using advanced imaging. The most significant warning signs include Thickness greater than 2 millimeters and the presence of subretinal Fluid surrounding the spot. Other factors involve patient Symptoms, such as a noticeable change or loss of vision, and the presence of Orange pigment on the surface of the nevus. The remaining factors include a Melanoma hollow seen on ultrasound, and a Diameter greater than 5 millimeters. The presence of multiple risk factors dramatically increases the chance of malignant change. Any growth in the size or thickness of a nevus is the most concerning indicator, necessitating immediate and specialized evaluation.
The Importance of Regular Eye Examinations
The best defense against potential issues with an ocular nevus is consistent, professional oversight. Since a choroidal nevus cannot be seen in a mirror, a routine, dilated eye examination is the only reliable way for an ophthalmologist to find and evaluate it. For nevi showing no suspicious features, an annual check is typically sufficient to ensure stability.
For nevi that present one or two risk factors, the monitoring schedule is often accelerated to every four to six months. During these exams, the ophthalmologist uses specialized instruments to take detailed photographs and measurements of the nevus. This comparative imaging is the standard method for tracking a nevus and identifying early malignant transformation. While UV light is a known risk factor for skin and conjunctival melanomas, wearing UV-protective sunglasses is an advised preventative measure. Proactive maintenance through regular check-ups allows for early detection, which is paramount for successful management.