An eye cancer is a cancer that starts in the eye. There are different types of eye cancers. To understand eye cancers, it helps to know something about the normal structure and function of the eye.
Parts of the eye
The eye has 3 major parts: the eyeball (globe), the orbit, and the adnexal structures.
Eyeball
The main part of the eye is the eyeball (also known as the globe), which is filled with a jelly-like material called vitreous humor. The eyeball has 3 main layers -- the sclera, the uvea, and the retina.
Sclera: The sclera is the tough, white, outer covering over most of the eyeball. In the front of the eye it is continuous with the cornea, which is clear to let light through.
Uvea: The uvea is the middle layer of the eyeball. It is where most melanomas of the eye develop. The uvea has 3 main parts:
The iris is the colored or pigmented part of the eye. It surrounds the pupil, the small opening that allows light to enter the eyeball.
The choroid is a thin, pigmented layer lining the eyeball that nourishes the retina and the front of the eye with blood.
The 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. It also contains cells that make aqueous humor, the clear fluid in the front of the eye between the cornea and the lens.
Retina: The retina is the inner layer of cells in the back of the eye. It is made up of specialized nerve cells that are sensitive to light. These light-sensing cells are connected to the brain by the optic nerve. Light enters the eye and passes through the lens, which focuses it on the retina. The pattern of light (image) appearing on the retina is sent through the optic nerve 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.
Orbit
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.
Adnexal structures
Finally, there are adnexal (accessory) structures such as the eyelids and tear glands.
Cancers that develop in these tissues are called adnexal cancers.
Cancers in the eye (intraocular cancers)
Two types of cancers can be found in the eye.
Primary intraocular cancers are cancers that start inside the eyeball. In adults, melanoma is the most common primary intraocular cancer, 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 (but it is extremely rare). These cancers are discussed in our separate document, Retinoblastoma.
Secondary intraocular cancers are cancers that have spread to the eye from another part of the body. These are not truly "eye cancers," but they are actually more common than primary intraocular cancers. The most common cancers that spread to the eye are breast and lung cancers. 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 is the most common type of cancer that develops within the eyeball in adults, but it is still fairly rare. Melanomas of the skin are much more common than intraocular melanomas.
Melanomas develop from pigment-producing cells called melanocytes. When melanoma develops in the eyeball, it is usually in the uvea, which is why these cancers are also called uveal melanomas. About 9 out of 10 intraocular melanomas develop in 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.
Nearly all of the remaining intraocular melanomas start in the iris. These 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 fairly 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).
Intraocular melanomas are generally made up of 2 different kinds of cells.
spindle cells: These are long, thin cells.
epithelioid cells: These cells are almost round but with some straight edges.
Most tumors are composed of both kinds of cells. The outlook is better if the tumors are mostly spindle cells as opposed to mostly epithelioid cells. Epithelioid tumors are more likely to metastasize (spread) to distant sites. If you have intraocular 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 starts in immune system cells called lymphocytes. It usually starts in lymph nodes, which are bean-sized collections of immune system cells. But lymphomas can also start in internal organs such as the stomach, lungs, and rarely in the eyes.
There are 2 main types 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).
Orbital and adnexal cancers
Cancers of the orbit and adnexa develop from tissues such as muscle, nerve, and skin around the eyeball 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, cancers of the eyelid are usually skin cancers, which are described in our documents on skin cancers (Melanoma Skin Cancer and Skin Cancer: Basal and Squamous Cell)
