The eye has 3 major parts: the globe, the orbit, and the adnexal structures.

The globe (eyeball) is filled with a jelly-like material called vitreous. The uvea and the retina are 2 important parts of the globe.

The uvea has 3 parts:

• iris -- the colored or pigmented part surrounds the pupil, the opening that controls the amount of light that enters the eyeball.

• choroid -- a thin, pigmented layer lining the eyeball that nourishes the retina and the front of the eye with blood.

• ciliary body -- contains the muscles inside the eye that change the shape of the lens so that the eye can focus on near or distant objects and cells that produce aqueous humor ( the fluid in the eye)..

The retina is like the film in a camera. It is in the back of the eyeball and has specialized nerve cells that are sensitive to light. These light-sensing cells are connected to the brain by the optic nerve. The pattern of light (image) appearing on the retina is sent from the retina to an area of the brain called the visual cortex, allowing us to see. Cancers that affect the eyeball are called intraocular (within the eye) cancers.

The second part of the eye, called the orbit, consists of the tissues surrounding the eyeball. These tissues include muscles that make the globe move in different directions and the nerves attached to the eye. Cancers of these tissues are called orbital cancers.

Finally, there are adnexal (or accessory) structures such as the eyelids and tear glands. Cancers that develop in these tissues are called adnexal cancers.

Cancers of the orbit and adnexa develop from tissues such as muscle, nerve, and skin and are just like their counterparts in other parts of the body. These are described in other American Cancer Society documents on cancers of muscle, nerve, skin, etc. For example, a cancer of the eyelid is usually a skin cancer like other skin cancers and is described in the American Cancer Society documents on skin cancers ("Melanoma " and "Nonmelanoma Skin Cancers"). Muscle cancer, called rhabdomyosarcoma, is described in another American Cancer Society document, "Rhabdomyosarcoma." Intraocular cancers are unique to the eye and are described here.

Types of Primary and Secondary Intraocular Cancers

Primary intraocular cancers are cancers that start inside the eyeball. Melanoma is the most common primary intraocular cancer in adults, followed by primary intraocular lymphoma. In children, retinoblastoma (a cancer arising from cells in the retina) is the most common primary intraocular cancer, and medulloepithelioma is the next most common. Retinoblastoma is discussed in a separate American Cancer Society document "Retinoblastoma." Medulloepitheliomas are extremely rare and are discussed briefly below.

Secondary intraocular cancers are cancers that have spread to the eye from another part of the body. The most common cancers that spread to the eye are breast and lung cancers. This occurs quite often when these diseases metastasize (spread). Usually these cancers spread to the part of the eyeball called the uvea. For more information on these types of cancers, refer to the specific American Cancer Society documents on these cancers.

Intraocular Melanoma (Melanoma of the Eye)

Intraocular melanoma (also called uveal melanoma) although rare, is the most common type of cancer that develops within the eyeball in adults. Melanomas of the skin are much more common than uveal melanomas and develop from pigment-producing cells called melanocytes. When melanoma develops in the eyeball, it is usually in the part of the uvea called the choroid. Choroid cells have the same kind of pigment as melanocytes in the skin, so it is not surprising that these cells sometimes form melanomas. Approximately 90% of intraocular melanomas develop in the choroid.

Nearly all of the remaining 10% of intraocular melanomas are melanomas of the iris. They are the easiest for the patient and doctor to see because they often arise in a pigmented spot on the iris that has been present for many years and then begins to grow. These melanomas usually are relatively slow growing, and they rarely spread to other parts of the body. For these reasons, people with iris melanomas generally have a good prognosis (outlook for survival).

Intraocular melanomas are generally composed of 2 different kinds of cells.

• spindle cells -- These are elongated cells.

• epithelioid cells -- These cells are almost round but with some straight edges.

Most of the tumors are composed of both kinds of cells. The outlook is best if the tumors are mostly spindle cells and worse if they are mostly epithelioid cells. Epithelioid tumors are more likely to metastasize (spread) to distant sites and be fatal. If you have ocular melanoma, your doctor can tell you which type of cells were found.

Primary Intraocular Lymphoma (Lymphoma of the Eye)

Lymphoma is a type of cancer that generally starts in lymph nodes, which are bean-sized collections of immune system cells. Lymphomas can also start in internal organs such as the stomach, lungs, and rarely in the eyes. There are 2 main categories of lymphoma -- Hodgkin disease and non-Hodgkin lymphoma. Primary intraocular lymphoma is always a non-Hodgkin lymphoma. Most people with primary intraocular lymphoma are elderly or have immune system problems such as the acquired immunodeficiency syndrome (AIDS). For more information about non-Hodgkin lymphoma in general, refer to the American Cancer Society document on that subject.

Medulloepithelioma

Medulloepithelioma is a very rare tumor that usually occurs in young children. Although most medulloepitheliomas are malignant, they rarely metastasize (spread). They usually cause eye pain and decreased vision. The diagnosis is made when a doctor finds a tumor mass in the eye by using an ophthalmoscope (instrument that helps doctors to look inside the eye). A biopsy (a procedure in which cells from the tumor are removed and examined under a microscope) is often performed to confirm the diagnosis. Treatment is with surgery. The doctor normally tries to remove only the tumor. If that is not possible, then the eye is removed. Last Revised: 10/16/2006