A tumor is a new growth of tissue in which the cells multiply and grow uncontrolled. Tumors may be benign or malignant. A benign tumor is composed of cells that grow abnormally but do not usually invade local tissues or spread (metastasize) to other areas of the body. A malignant tumor or cancer contains cells that grow uncontrolled and invade surrounding areas or spread.
A choroidal melanoma is a malignant tumor composed of melanocytes—pigment (coloring matter) containing and producing cells normally present in the choroid (the pigmented vascular layer beneath the retina). If ignored, this type of tumor may spread to areas around the eye or metastasize to distant areas of the body (i.e., the liver or lung) and can cause death. Early detection and treatment may prevent these devastating events.
Fortunately, tumors of the eye are rare; however, in adults,choroidal melanoma is the most common intraocular malignancy. At present, in the United States, only about 1200 cases of choroidal melanoma, or about 5 cases per million of the population are diagnosed each year. The average age of patients with this type of tumor is 50 years. The incidence of melanoma is highest from ages 50 to 70. The incidence is approximately the same for men and women, but in the age range of 18 to 50 years, women are more likely to suffer from choroidal melanoma. Very few cases occur in people under 30 years old. Choroidal melanomas are seen more frequently in whites.
The cause of choroidal melanoma is unknown. Inheritance seems to be of little importance. There is some evidence that environmental factors (carcinogens such as cigarette smoke) may play a role. Environmental factors may influence benign pigmented cells (preexisting pigment spots present normally in many people’s eyes that are similar to freckles on the skin) to change into malignant cells.
Choroidal melanomas may produce no symptoms initially if located away from the macula (the area of the retina used for central vision, the vision we use for reading or seeing faces). On the other hand, a tumor that develops next to or in the macula may produce distorted and/or reduced vision. Tumors located away from the macula may produce changes in the visual field (side of vision) as they enlarge, and the patient may complain of a dark area or shadow to one side. In addition, as these tumors enlarge, they may cause changes in the vitreous (the gel-like substance that fills the eye) and produce flashes of light or floaters (black spots). Fluid may also leak under the retina from large tumors, and this may cause a retinal detachment (elevation of the retina from its normal position), with distorted and/or decreased vision. A person rarely notices increased pigmentation on the sclera (darkness on the white portion of the eye), and it is uncommon for someone with a choroidal melanoma to complain of pain unless a complication such as glaucoma (pressure in the eye) has developed. Most choroidal melanomas are therefore discovered by the ophthalmologist on routine examination.
Several examination modalities are used by the ophthalmologist to aid in the diagnosis of choroidal melanomas. The ophthalmologist examines the external portion of the eye for abnormal pigmentation or dilated vessels. The inside of the eye is viewed through a special lighted instrument called an ophthalmoscope. This is the most important step in the diagnosis and is a part of the routine eye checkup. The ophthalmologist initially becomes suspicious of this tumor by the presence of an elevated mass in the eye. The ultrasound examination, a technique that uses sound waves to produce a photograph of the tumor, helps confirm the diagnosis because most melanomas produce a recognizable picture. These tumors often look like a dome or a mushroom on ultrasound. Another technique that helps distinguish melanomas from other ocular lesions is fluorescein angiography. A special camera takes pictures of the inside of the eye after injection of the dye fluorescein into a vein in the forearm. Sometimes it is difficult to tell a melanoma from other masses that can be seen in the eye and other, more specialized tests may be useful. Recently, investigations at the University of Illinois at Chicago have shown that the use of magnetic resonance imaging (MRI) is promising in distinguishing choroidal melanoma from other eye tumors. MRI is a technique that uses magnetic energy to produce a picture of the tumor.
Patients with choroidal melanomas also need to have a systemic evaluation (examination of the entire body) to look for possible spread of the tumor.
There are many forms of treatment available for choroidal melanoma. The oldest technique has been nucleation, which is removal of the eye. Over the years ophthalmologists have tried other treatments to save the eye and as much vision as possible while also attempting to prevent metastases (spread of the tumor) and to prolong the patient’s life. These alternative techniques include radioactive plaque therapy (sewing a disc with radiation to the eyewall), external radiation therapy (using charged radioactive particles that are directed into the eye to treat the tumor), and local resection techniques (cutting out the tumor while attempting to save the remainder of the eye).
Not all melanomas can be treated by any one of these techniques, and it is not yet known which treatment provides the greatest chance of prolonging a patient’s life.
Medical centers throughout the country are participating in the collaborative ocular melanoma study, a national study, comparing various treatment modalities to determine which has the best patient survival rate.
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