is a cancer of the pigment-producing cells (melanocytes) in the middle layer of the eye, called the uveal tract. The uveal tract has 3 main parts: (1) the choroid (the tissue layer filled with blood vessels); (2) the ciliary body (the ring of muscle tissue that changes the size of the pupil and the shape of the lens); and (3) the iris (the colored part of the eye). Most cases (90%) of intraocular melanoma develop in the choroid, called choroidal melanoma; the ciliary body is less commonly a site of origin, and the iris is the least common. Each manifests with different clinical features and symptoms. Treatment depends on the site of origin (choroid, ciliary body, or iris), size and location of the tumor, the age of the individual, and other factors. Source: Genetic and Rare Diseases Information Center (GARD), supported by ORDR-NCATS and NHGRI.