Cancer is a group of many related diseases. All cancers begin in cells
, the body's basic unit of life. Cells make up tissues, and tissues make up the organs of the body.
Normally, cells grow and divide to form new cells as the body needs them. When cells grow old and die, new cells take their place. Sometimes this orderly process goes wrong. New cells form when the body does not need them, and old cells do not die when they should. These extra cells can form a mass of tissue called a growth or tumor
Tumors can be benign or malignant.
Benign tumors are not cancer.
Usually, doctors can remove them. Cells from benign tumors do not spread to other parts of the body. In most cases, benign tumors do not come back after they are removed. Most important, benign tumors are rarely a threat to life.
Malignant tumors are cancer.
They are generally more serious. Cancer cells can invade and damage nearby tissues and organs. Also, cancer cells can break away from a malignant tumor and enter the bloodstream or the lymphatic system. That is how cancer cells spread from the original (primary
) tumor to form new tumors in other organs. The spread of cancer is called metastasis
The main part of the eye is the eyeball (also known as the globe), which is mostly filled with a jelly-like material called vitreous humor
. The eyeball has 3 main layers: the sclera, the uvea, and the retina.
is the tough, white covering over most of the outside of the eyeball. In the front of the eye it is continuous with the cornea, which is clear to let light through.
is the middle layer of the eyeball. It is where most melanomas of the eye develop and has three main parts:
- The iris is the colored area at the front of the eye (the "eye color"). It can be seen through the clear cornea. The pupil is in the center of the iris and it changes size to let more or less light into the eye.
- The ciliary body is a ring of tissue with muscle fibers that change the size of the pupil and the shape of the lens. It is found behind the iris. Changes in the shape of the lens help the eye focus. The ciliary body also makes the clear fluid that fills the space between the cornea and the iris.
- The chroid is the layer of blood vessels that bring oxygen and nutrients to the eye. About 9 out of 10 intraocular melanomas develop in the choroid. Choroid cells make the same kind of pigment as melanocytes in the skin, so it is not surprising that these cells sometimes form melanomas.
The retina is the inner layer of cells in the back of the eye, made up of specialized nerve cells that are sensitive to light, which 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.
There are two types of cancer that develop within the eye. They are called intraocular
Intraocular Eye Cancer
This type begins in the uvea of the three layers of the wall of the eye. Cancers that affect this section of the eyeball are called intraocular (within the eye) cancers. 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. Secondary intraocular cancers start somewhere else and then spread to the eye. The most common cancers that spread to the eye are breast and lung cancers.
Intraocular Melanomas are generally made up of two different kinds of cells, which are:
These are long, thin cells.
These cells are almost round but with some straight edges.
Intraocular Melanoma is the most common type of cancer that develops within the eyeball in adults but is fairly rare - melanomas of the skin are much more common than intraocular melanomas.
Primary Intraocular Lymphoma is always a non-Hodgkin lymphoma. Most people with primary intraocular lymphoma are elderly or have immune system problems. This cancer is often seen along with lymphoma of the brain (Central Nervous System Lymphoma.)
Cancer that forms in the tissues of the retina (the light-sensitive layers of nerve tissue at the back of the eye) is called retinoblastoma
. Retinoblastoma usually occurs in children younger than 5 years. It may be hereditary or nonhereditary (sporadic.) The tumor may be in one eye or in both eyes. Retinoblastoma rarely spreads from the eye to nearby tissue or other parts of the body.
External Eye Cancers
The second part of the eye, called the orbit
, consists of the tissues surrounding the eyeball. These tissues include muscles that move the eyeball in different directions and the nerves attached to the eye. Cancers of these tissues are called orbital cancers.
There are also cancers that affect the adnexal
(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 around the eyeball and function similarly to other tumor types of the body.