The choroid is a layer of tissue rich in blood vessels at the back of the eye, between the sclera and the retina. This layer provides oxygen and nutrients to the outer part of the retina. Similar to how pigmented spots appear on the skin, they can also develop within the eye. These spots can be a common, non-cancerous choroidal nevus, often called an eye freckle, or the much rarer, malignant choroidal melanoma.
Defining the Lesions
A choroidal nevus is a benign collection of pigment-producing cells called melanocytes, similar to common moles or freckles on the skin. They are relatively common, present in about 5% of the adult population. These lesions are flat or only slightly elevated and do not interfere with vision.
In contrast, choroidal melanoma is a malignant tumor that arises from the same melanocyte cells and is characterized by uncontrolled cell growth. Although it is the most common primary eye cancer in adults, it is rare, with an estimated six new cases per million people each year. The vast majority of choroidal nevi remain stable and never undergo malignant transformation.
Clinical Signs of Transformation
An ophthalmologist looks for high-risk characteristics that indicate a choroidal nevus may be transforming into a melanoma. A primary sign is an increase in the thickness of the lesion. While nevi are flat or minimally elevated, melanomas are often thicker, generally over 2 millimeters, and show documented growth over time.
Another warning sign is the presence of fluid leaking from the lesion, known as subretinal fluid. This leakage can cause the retina to detach and may be a sign of a more active process. The appearance of orange pigment on the surface of the spot is also an indicator more commonly associated with melanoma than with a benign nevus.
While most choroidal nevi are asymptomatic, the sudden onset of symptoms can be a red flag. Patients might experience flashing lights, an increase in floaters, or a noticeable change in their field of vision. These symptoms often occur because the growing tumor or associated fluid is interfering with the retina’s function. The location of the lesion is also taken into account; a nevus located near the optic nerve head is monitored more closely.
Diagnostic and Monitoring Protocols
To determine the nature of a pigmented lesion in the choroid, eye care professionals use detailed examination and advanced imaging technologies. The first step is to establish a baseline by taking detailed photographs of the back of the eye, known as fundus photography. This documentation is used for future comparisons to detect any changes in the lesion’s size, shape, or color.
Specialized imaging tools provide a more in-depth view. Optical Coherence Tomography (OCT) is a non-invasive test that uses light waves to take cross-section pictures of the retina. This allows the doctor to measure its thickness and detect the presence of subretinal fluid. Ocular ultrasound, or B-scan, uses sound waves to create an image of the inside of the eye, helping to measure thickness and evaluate the internal characteristics of the tumor.
For a choroidal nevus that appears to be low-risk, the standard approach is “watchful waiting.” This involves a follow-up visit six months after the initial discovery, and then annual check-ups if the lesion remains stable. If a nevus has one or more suspicious features, a more frequent monitoring schedule, such as every four to six months, will be recommended to watch for any signs of growth or change.
Managing a Choroidal Melanoma Diagnosis
Once a definitive diagnosis of choroidal melanoma is made, the primary goals of treatment are to destroy the cancerous tumor, prevent it from spreading (metastasis), and preserve as much of the patient’s vision as possible. The specific treatment plan is determined after staging the cancer to see if it has spread beyond the eye.
The most common treatment for choroidal melanoma is radiation therapy. One form, known as plaque brachytherapy, involves surgically placing a small, radioactive disc on the outside of the eye, directly over the tumor. This plaque delivers a concentrated dose of radiation to the melanoma over several days before it is removed. Other forms of radiation, such as proton beam therapy, can also be used to target the tumor.
In some cases, other treatments may be considered. Laser therapy can be used to destroy smaller tumors. For very advanced or large melanomas, removal of the eye, a procedure called enucleation, might be necessary. Following treatment, patients are monitored by an eye cancer specialist and an oncologist to check for any recurrence of the tumor or spread of the cancer.