A melanoma is a type of cancer that arises from pigmented cells. We have pigmented cells, called melanocytes, in many parts of our bodies, including the eye. As most of these melanocytes are in the skin, the most common place for a melanoma to occur is in the skin. Consequently, most of what is written about melanoma is referring to melanomas of the skin. However, melanomas arising in other tissues, including the eye, are different from melanomas of the skin, so one cannot apply what we know about skin melanomas to melanomas of the eye. For instance, melanomas of the eye are rare, occurring in only 6 patients/million population/year. Also, melanomas of the eye have little correlation to ultraviolet light exposure, the most common risk factor for developing melanoma of the skin. In most cases of choroidal melanoma, there are no identifiable environmental or genetic factors that led to the development of the melanoma. Choroidal melanoma is one of the many tumors that arise sporadically; that is, without any predisposing risk factor. The average age for developing a choroidal melanoma is 65.
Melanomas of the eye develop in a layer of tissue called the choroid (also called the uvea) that is underneath the retina (see figure). Many patients with choroidal melanoma have no symptoms, and the tumor in their eye is detected on routine examination. Other patients develop blurred vision. The blurred vision in most patients is due to fluid that collects around the tumor and causes a retinal detachment. Sometimes this fluid collects rapidly or shifts underneath the center of the retina causing a sudden change in vision. This sudden change in vision gives the impression that the tumor is growing rapidly, but in actuality the suddenness is due to position of the subretinal fluid rather than growth of the tumor. Most choroidal melanomas are very slowly growing tumors.
When a pigmented lesion is found beneath the retina, it could be a benign or non-cancerous growth called a nevus; or a malignant, “cancerous” growth, a melanoma. There are certain features of pigmented lesions that are used to distinguish benign from malignant lesions. These are the size, appearance on examination, and the way the lesion appears on special tests. These tests include ultrasound, and photographic tests which include fluorescein angiography (FA) and optical coherence tomography (OCT).
Echography: This is a non invasive test in which sound waves are transmitted through the eye using a hand piece or a “probe”. The probe rests on the eyelids or the eye surface. The sound waves are reflected off the surface of the retina and the deeper layers including the choroid, and are received in the probe. The reflected sound waves can be analyzed to measure the thickness of the lesion, as well as some of the internal features of the lesion. Melanomas have a characteristic appearance on ultrasound that helps distinguish them from other tumors.
Fluorescein Angiography: In this test, a dye called fluorescein is injected into a vein in the arm. A series of photographs is taken as the dye circulates through the blood vessels in the eye. Some features of the blood vessels in tumors can be helpful in distinguishing the different types of tumors.
Optical Coherence Tomography: This test is much like an ultrasound, only instead of using sound waves, it uses light. The light used for this test is projected into the eye through the pupil. The light reflected back can be analyzed to judge if there is fluid under the retina. The presence of fluid under the retina is one of the features that can be used to help distinguish melanomas from nevi.
Using the clinical features and these tests, a correct diagnosis of nevus or melanoma can be determined in most cases. In certain cases, lesions need to followed over time, due to uncertainty. Rarely, a biopsy of the tumor is obtained when the non-invasive evaluation is inconclusive and an answer is needed.
Once a tumor is diagnosed as melanoma, treatment is needed to prevent further growth of the tumor, or spread of the tumor from the eye to other sites. The type of treatment that is recommended depends on the size and location of the melanoma. For small and medium sized melanomas the most common form of treatment is radiation. For large melanomas (thickness > 8mm or basal diameter > 16 mm) the most common form of treatment is removal of the eye (enucleation). In some cases large tumors are treated with radiation if the treatment is feasible, and there are compelling reasons to preserve the eye, e.g. blindness in the other eye. Please see separate information for the details of radiation and enucleation. Other treatments that may be employed in special circumstances are laser photocoagulation, transpupillary thermotherapy, cryotherapy, or local resection of the tumor.
Prior to treatment, certain screening tests are obtained to evaluate for the presence of the melanoma at sites distant from the eye (metastasis), and to serve as a baseline for comparison to future tests. At the time of diagnosis of a melanoma of the eye, involvement of other sites can only be detected with current tests in approximately 2% of patients. However, there could be microscopic spread that is not detectable with preoperative blood tests or scans.
The most common sites of distant involvement with melanoma of the eye are the liver and the lungs. As mentioned above, it is unusual to find evidence of involvement at the time of diagnosis of the eye tumor. The peak incidence of the appearance of liver involvement is about 4 years after treatment of the eye tumor. However metastasis may appear even decades after treatment, so patients must be followed indefinitely after treatment to monitor for metastasis. The likelihood of metastasis is dependent on the size and the type of melanoma cells present in the tumor. Tests are being refined that allow more precise prediction of the risk for metastasis. These tests include the appearance of the cells under a microscope and evaluations of the genetic material within the cells. More information on the availability of these tests can be obtained from Dr. Wilson.
Follow up Care
The care specific for either radiation or enucleation is covered with those patient information sections. However, regardless of form of treatment of the eye tumor, patients with choroidal melanoma need to make a conscious decision about follow up screening for metastatic disease. Unfortunately, there is not currently any curative treatment for choroidal melanoma that has spread to the liver or lungs. There are “protocol” treatments that are being evaluated for efficacy in treating metastatic disease. If involvement of the liver or lungs were to develop a patient might want to participate in these protocols. Also, it generally benefits patients to know as early as possible as to the presence of metastatic disease. Consequently, we recommend a general physical examination and blood tests to screen for liver involvement every 6 months, and an annual scan of the liver and x-ray of the lungs. Because there is not a curative treatment for melanoma if it does spread to the liver or lungs, some patients opt not to have any testing done.
Shown above is a typical choroidal melanoma. The melanoma is the pigmented lesion lying between two normal retinal vessels and indicated with the arrow. Adjacent to the photograph is an ultrasound image of the same eye. The melanoma creates a some shaped elevation, shown with arrow. A tumor such as this is typically treated with radioactive plaque.
There are three components to the radioactive plaque, a gold shield with eyelets for fixating the plaque to the eye, a plastic insert that holds the radioactive seeds, and the radioactive seeds. The insert and radioactive seeds fit inside the gold shield.
During surgery the radioactive plaque is sutured to the outside of the eye, overlying the tumor. The location of the plaque is verified during surgery using the ultrasound. The margins of the plaque are indicated with the arrows.
Many months following surgery, the melanoma has regressed. There is an area of atrophy surrounding the tumor in the color photograph and the thickness of the tumor has diminished as is evident in the adjacent ultrasound.