Cancer can develop in the eyeball or in nearby structures, such as the eyelids or orbit. Tumors of the eye are most often metastatic tumors that have spread from other parts of the body. The most common primary cancers of the eyeball are melanoma of the eye (uveal/intraocular melanoma) and retinoblastoma. In adults, melanoma of the eye is the most frequently diagnosed primary eye cancer, and forms in the uvea (middle layer of the eye) in pigment-producing cells called melanocytes. Melanocytes are found mainly in the skin and make the pigment that gives your skin its color, but they can also be found in other places such as the eyes and hair.