Choroidal melanoma is a rare form of cancer that originates within the eye. This malignancy develops in the choroid, a vascular layer located between the retina and the sclera, the eye’s white outer wall. Although it is the most common primary cancer to develop inside the adult eye, its overall occurrence is infrequent.
Understanding Choroidal Melanoma
The choroid is a thin, pigmented, vascular layer of tissue positioned between the sclera, the outer white part of the eye, and the light-sensitive retina. Its primary function involves supplying oxygen and essential nutrients to the outer layers of the retina and the optic nerve, which have high metabolic demands. The choroid also contributes to regulating the eye’s internal temperature.
Choroidal melanoma originates from melanocytes, the pigment-producing cells found within this vascular layer of the eye. While it shares the same cellular origin as skin melanoma, choroidal melanoma is a distinct form of cancer. It arises when these melanocytes undergo uncontrolled growth, forming a tumor. Most choroidal melanomas are believed to develop from pre-existing melanocytic nevi, or “freckles,” within the choroid.
Despite being the most frequently diagnosed primary malignant tumor inside the eye in adults, choroidal melanoma remains a rare condition in the general population. Its incidence in the United States is approximately 5 to 6 cases per million people annually.
Recognizing Symptoms and Risk Factors
Choroidal melanoma often develops without noticeable symptoms in its early stages, frequently diagnosed incidentally during routine eye examinations. When symptoms do occur, they can include blurred vision, the sensation of flashing lights (photopsia), or the appearance of new floaters in the field of vision. A growing dark spot on the iris, a change in pupil shape, or a loss of peripheral vision may also indicate the presence of a tumor.
Symptoms typically emerge as the tumor grows and begins to affect vision, potentially causing retinal detachment. While pain is an uncommon symptom, it can occur in rare instances.
Several factors are associated with an increased likelihood of developing choroidal melanoma. Individuals with light skin tones, light-colored eyes, and those who sunburn easily or have difficulty tanning are at higher risk. Other predispositions include the presence of atypical moles (dysplastic nevus syndrome), certain genetic conditions like ocular melanocytosis, or a pre-existing choroidal nevus. The risk also tends to increase with age.
Diagnosis and Treatment Approaches
Choroidal melanoma is often first suspected during a comprehensive dilated eye examination, where an eye care specialist may observe a dark spot on the back of the eye. To confirm the diagnosis and assess the tumor, several specialized tests are employed. Ocular ultrasound is commonly used to measure the tumor’s size, evaluate its internal characteristics, and determine if it has extended beyond the eye.
Fluorescein angiography and indocyanine green angiography involve injecting a dye into the bloodstream to visualize blood vessels and detect any blockages or leakage associated with the tumor. Optical coherence tomography (OCT) offers high-resolution cross-sectional images of the retina, helping to identify subretinal fluid or assess any damage to the retinal layers. In some cases, if other tests are inconclusive, a biopsy may be performed to analyze a tissue sample.
Treatment approaches for choroidal melanoma vary significantly, tailored to the tumor’s size, its location within the eye, and the patient’s overall health. Radiation therapy is a common eye-sparing option, with plaque brachytherapy being widely used. This procedure involves surgically attaching a small gold plaque containing radioactive seeds, such as Iodine-125 or Palladium-103, directly onto the eye over the tumor. The plaque delivers localized radiation to destroy cancer cells and is typically removed after several days. Proton beam radiation, an external beam therapy, is another form of radiation that can be used.
For larger tumors, or when other treatments are not suitable, surgical removal of the eye, known as enucleation, may be recommended. Smaller tumors located in the front of the eye might be managed with iridocyclectomy, which involves removing a portion of the iris and ciliary body. Laser treatments, such as laser photocoagulation or photodynamic therapy (PDT), use focused light or light-activated drugs to destroy tumor cells, sometimes used for smaller lesions. Very small tumors might initially be observed with close monitoring rather than immediate treatment.
Prognosis and Monitoring
Tumor size is a significant predictor, with larger tumors generally associated with a less favorable prognosis. The location of the tumor within the eye and the specific cell type, particularly the presence of epithelioid cells, can also affect outcomes. Additionally, certain genetic characteristics of the tumor play a role in predicting its behavior.
Choroidal melanoma has a tendency to spread through the bloodstream, most commonly to the liver. Liver metastasis occurs in a significant number of cases and can reduce survival time. Other less frequent sites of spread include the lungs, bones, and skin.
Ongoing monitoring is therefore an important part of post-treatment care to detect any local recurrence in the treated eye or the development of distant metastases. Regular follow-up appointments with an ophthalmologist are necessary for ocular health assessments. Additionally, collaboration with an oncologist is often recommended, involving periodic liver function tests and imaging studies like abdominal ultrasound, CT, or MRI scans to screen for metastatic disease.