context: Melanoma is a kind of cancer that develops in cells that give your skin, eyes, and hair their color. These cells are called melanocytes. Melanoma usually shows up on the skin, but it also can happen in your eyes. When it does, doctors call it ocular melanoma. Some ocular cancers form on the surface of the eye and the eyelid. Those are closely related to melanomas of the skin in other parts of your body. But ocular melanoma can also form inside the eye. Cancer cells grow in the uvea, a layer of tissue under the white part of your eye. The uvea contains melanocytes. Uveal melanoma is another name for ocular melanoma. This is the most common form of eye cancer in adults, but it's still rare. Your odds of getting it are about 6 in 1 million. It can cause vision problems and can be serious if it spreads to other organs. Doctors don't know exactly what causes ocular melanoma. As with skin cancer, people with fair skin, blond or red hair, and light-colored eyes are more likely to get it. But unlike skin cancer, there's no hard evidence that links ocular melanoma to ultraviolet ( UV) rays, the kind you're exposed to from sunlight or a tanning bed. Still, you should avoid too much UV exposure for other health reasons. The uvea contains three parts: Iris: the colored part in the front of the eye Ciliary body: the part that releases fluid into your eye and changes the shape of the lens to help your eye focus Choroid: the part that contains blood vessels to nourish your eye Cancer can form in each of these three parts. It's most likely to grow in the choroid, followed by the ciliary body and then the iris. Some people have cancer in more than one of these three areas at the same time. Melanoma of the iris is the least serious of the three types. Cancers of the ciliary body may be hardest to treat. When cancer is in the ciliary body, it can push the lens of the eye out of place and blur your vision. Very rarely, this cancer can grow on the eyelid or the clear, thin coating over the white of the eye called the conjunctiva. Choroidal nevi are little freckles -- colored areas in the back of your eye. They're benign, or noncancerous, ocular tumors that form on the iris or choroid. Because they're not cancer, nevi can't spread to other parts of your body. Nevi are much more common than cancer in the eye. About 1 out of every 10 people has at least one of them. There's a slight chance of choroidal nevi turning into cancer, just like the moles on your skin. Out of every 500 eye freckles, 1 will turn into cancer within 10 years. People with light-colored skin and eyes are at greater risk for melanoma of the eye. You're more likely to get this cancer if you have a lot of freckles or moles on your body. People with something called atypical mole syndrome are more likely to develop melanoma on the skin and also may be more likely to get ocular melanoma. This condition can cause more than 100 moles to form on a person's body, some with abnormal shapes and sizes. Scientists are looking into whether parents can pass a higher risk for ocular melanoma to their children. The cancer usually develops in the middle layer of the eyeball, which holds the blood vessels that feed your inner eye. You may not notice any symptoms at first. People with choroidal or ciliary body melanoma often don't have symptoms. Your eye doctor might find the cancer during a routine eye exam. As a tumor grows, it can cause floating black spots, light flashes, or loss of eyesight. It sometimes changes the shape of your pupil (the dark circle in the middle of your eye). In other cases, the tumor forms on the iris, the part that gives your eye its color. If this happens, it's easier to spot early. Between 2% and 5% of people have a tumor in the conjunctiva -- the moist membrane that covers your eye. A choroidal nevus almost never causes symptoms. Very rarely, it can leak fluid and lead to flashing lights or vision loss. Doctors often notice a melanoma during a routine eye exam because the tumors usually are darker than the area around them or leak fluid. Your doctor may want to do additional tests: Ultrasound: High-frequency sound waves are used to make images of the inside of your eye. Fluorescein angiography: You'll get a special dye put into your bloodstream through a vein in your arm. The dye will travel up to your eye. Your doctor then uses a special camera to take pictures of the inside of your eye. This can help them find any blockage or leak. Photographic imaging: Your eye doctor might take a picture of a nevus at each visit to track its growth. Bigger, thicker nevi are more likely to turn into cancer. In rare cases, when these tests don't give a definite answer, your doctor might take some tissue from your eye to get a closer look under a microscope. This is called a biopsy. If your ocular tumor is small or noncancerous, you might not have to get it treated right away. Your doctor may just want to check it regularly to see if it grows or causes problems. If caught before it spreads outside the eye, doctors can successfully treat most ocular melanomas. Your treatment may include: Radiation: The most common form uses a shield shaped like a small bottle cap to hold radioactive seeds against the outside of your eyeball over the tumor. This is called a plaque, and it's put in and taken out with surgery. It stays in place about 4 days. Most people say it doesn't bother them much. Another form of radiation treatment uses a machine that hits the tumor with radioactive particles. The treatment is usually spread over several days. Lasers: Your doctor uses infrared light to kill a small tumor and seal off the nearby blood vessels to keep the cancer from spreading. This typically involves sending a laser beam through your pupil at low power so it can attack the cancer cells without damaging your eye. Surgery: In some cases, your doctor might have to take out part of your eye to remove the tumor. Most tumors in the iris are treated this way. If a tumor is big enough, your doctor might have to remove your eye and replace it with a prosthetic eye to provide a normal appearance. Your doctor probably will recommend you get regular CT scans or MRIs to make sure the cancer hasn't spread. A CT scan (computerized tomography) takes X-rays from different angles and puts them together to show a more complete picture. An MRI (magnetic resonance imaging) uses powerful magnets and radio waves to make detailed images. Your doctor will focus on your liver, since that's where a new tumor is most likely to start. If it has, the earlier it's found, the more choices you have for treatment. Your treatment may damage your vision, so you also may need to see an eye doctor (ophthalmologist) regularly.