Eye cancers can be either primary or secondary, depending on where they first occur. Primary eye cancers originate inside the eyeball. Types of primary eye cancer include:

• Intraocular melanoma. Also called uveal melanoma, intraocular melanoma is the most common primary eye cancer in adults. Typically, melanomas develop from melanocytes, the cells that produce pigment in the skin. When melanoma affects the eyeball, it normally develops in a part of the uvea called the choroid, which contains pigment similar to the melanocytes found in skin. The choroid lines the eyeball and delivers blood to the retina and the front of the eye.
  
  According to the American Cancer Society (ACS), approximately 90 percent of intraocular melanomas affect the choroid. The remaining 10 percent of intraocular melanomas begin in the iris (the colored portion of the eye that regulates light). These melanomas are sometimes easier to see. They usually appear in a pigmented part of the iris and may exist for several years before they suddenly begin to grow. Intraocular melanomas of the iris are normally slow growing and less commonly invade other regions of the body. For these reasons, individuals with iris intraocular melanomas typically have a better prognosis (predicted outlook for survival).
  
  Intraocular melanomas are typically composed of two different types of cells. These include elongated spindle cells and round epithelioid cells. Individuals whose tumors are mainly composed of spindle cells generally have a better prognosis because epithelioid cells are more likely to spread (metastasize) to distant sites and become fatal.
  
  
• Primary intraocular lymphoma. Lymphoma is a form of cancer that usually affects older adults and typically begins in the lymph nodes, the bean-sized groups of immune system cells that help ward off infections and cancers. Lymphoma can also arise in other organs, including the eyes. Lymphoma can be divided into two main types: Hodgkin’s lymphoma and non-Hodgkin’s lymphoma. Primary intraocular lymphoma is a type of non-Hodgkin’s lymphoma that usually affects elderly people and individuals with compromised immune systems (e.g., patients with AIDS).
  
  
• Retinoblastoma. Retinoblastoma is a cancer that begins in the retina, the nerve tissue at the back of the eye. It mainly affects infants and children under age 5. However, this rare condition affects only four out of every 1 million children, according to the ACS. It is even rarer in adults. Retinoblastoma that is confined to the retina is called intraocular retinoblastoma. Retinoblastoma that extends beyond the eye, into surrounding tissues or other parts of the body is called extraocular retinoblastoma.
  
  Most children with retinoblastoma are affected in only one eye. Cases in which both eyes are affected are nearly always caused by an inherited type of the cancer. Children with retinoblastoma are at greater risk for developing a brain tumor (trilateral retinoblastoma) during treatment as well as other types of cancer in later life.
  
  
• Embryonal medulloepithelioma. Medulloepithelioma is an extremely rare tumor in the ciliary body of the eye that occurs in young children. Most medulloepitheliomas are malignant, but they do not usually spread to other parts of the body. Medulloepitheliomas typically cause eye pain and impaired vision. In severe cases, treatment for medulloepithelioma involves surgical removal of the eye (enucleation).