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Eye cancer refers to a cancerous growth in any part of the eye. Some eye cancers are primary, while others represent metastases from primary cancers elsewhere in the body.
All types of eye cancer are rare in comparison to other cancerous tumors. According to the American Cancer Society, 2,090 people in the United States will be diagnosed with cancer of the eye or orbit in 2004, and 180 persons will die from the disease.
Eye cancers can be grouped into three basic categories according to their location in the eye: tumors of the eyelid and conjunctiva; intraocular tumors; and orbital tumors. This article will focus on retinoblastoma, the most common eye cancer in children, and intraocular melanoma, the most common eye cancer in adults.
Retinoblastoma can occur at any age but is most often seen in children younger than five. About 200 children a year are diagnosed with it in the United States. Retinoblastoma starts with a small tumor in the retina, the tissue that lies at the very back of the eye. In growing children, the retina originates from cells called retinoblasts that grow and divide very quickly. These cells eventually become the mature cells of the retina when they stop growing. In the case of retinoblastoma the retinoblasts don't stop growing and form a tumor that can continue to grow and cause further complications if not treated quickly.
Retinoblastoma typically has three classifications: intraocular, extraocular and recurrent retinoblastoma. In the intraocular form the cancer can be found in one or both eyes but not in tissue external of the eye. In the extraocular form the cancer has spread outside the eye. It can spread to the tissue surrounding the eye or it can invade other areas of the body. In the recurrent form the cancer returns after already being treated. It may recur in the eye, its surrounding tissues, or elsewhere in the body.
Intraocular melanoma is a rare cancer overall, yet it is the most common eye cancer seen in adults. Intraocular melanoma occurs when cancer cells are found in the uvea of the eye. The uvea includes the iris (the colored portion of eye), the ciliary body (an eye muscle that focuses the lens) and the choroid (found in the back of the eye next to the retina).
Intraocular cancer of the iris usually grows slowly and usually doesn't spread. The tumor is seen on the iris as a darker spot than the surrounding area. Intraocular cancer of the choroid or ciliary body occurs in the back of the eye. They are classified by size with a small tumor being 2-3 mm or smaller and a medium or large tumor being bigger than 3 mm.
Intraocular cancer can spread and become extraocular as well. If not found and treated early enough it can spread to the surrounding tissues, the optic nerve or into the orbit (eye socket).
Causes and symptoms
Genetics is thought to play a role in eye cancer. In regards to retinoblastoma, it is believed that if a tumor develops only in one eye then it isn't hereditary. However, if a tumor occurs in both eyes then it is hereditary. Those who have hereditary retinoblastoma have a rare risk of developing a tumor in the brain and should be monitored on a regular basis.
The causes of intraocular melanoma are not fully understood as of the early 2000s. Age is a factor as well as genetic inheritance. In 2004, a group of ophthalmologists in Scotland identified mutations in the BRAF gene in samples of tissue taken from conjunctival melanomas. Interestingly enough, this type of cancer is seen most often in white people from a northern European descent.
The symptoms of this type of cancer usually begin with blurred vision and tenderness of the eye. Advanced symptoms may include loss of vision. If these symptoms persist a person should make an appointment with an eye specialist.
The diagnosis of eye cancer is usually made by an ophthalmologist, who is a doctor who specializes in treating eye disorders. In the case of cancerous growths, the doctor is usually able to see the tumor through the pupil or directly on the iris if the cancer is intraocular melanoma of the iris. Because the doctor can usually readily see the tumor a biopsy is rarely needed.
An ultrasound or a fluorescein angiography are two tests doctors use to further diagnose eye cancers. In an ultrasound sound waves are pointed at the tumor and depending on how they reflect off the tumor the doctor can better diagnose it. In a fluorescein angiography a fluorescent dye is injected into the patients arm. When this dye circulates through the body and reaches the eye a series of rapid pictures are taken through the pupil. The tumor will show up in these photos.
Once a diagnosis has been made, the treatment can begin.
The treatment depends on how far advanced the tumor is. If the tumor is in the advanced stages and there is little hope of regaining vision the most effective treatment is an enucleation, the removal of the eye. Enucleation obviously is a drastic treatment and is avoided if possible. Other eye surgeries include the following:
- choroidectomy: removal of part of the choroid
- iridectomy: removal of part of the iris
- iridocyclectomy: removal of parts of the ciliary body and parts of iris
- iridotrabeculectomy: removal of parts of the supporting tissues around the cornea and iris
In eye cancer where the tumor is small and there is a good chance that the vision will be restored less drastic measures than the above surgeries are taken. Radiation and chemotherapy are two courses of treatment that help in killing off the existing tumor and preventing its spread into other areas of the body. Specific anticancer drugs that are used in treating melanomas of the eye include gemcitabine and treosulfan.
Besides radiation and chemotherapy there are other methods of treating eye cancer. Cryotherapy uses extreme cold to destroy the cancer cells. Thermotherapy uses heat from a laser to destroy the cancer cells. Photocoagulation uses a laser to destroy blood vessels that supply the tumor with nutrients. If the tumor isn't advanced these are good options to treat it in order to avoid losing an eye. The chief drawback of thermotherapy is that some visual acuity may be lost in the treated eye.
A radiation/surgical treatment for eye cancer is brachytherapy. A small plaque with radioactive iodine on one side and gold on the other is stitched to the eye behind the tumor with the radioactive iodine facing the tumor. The gold is used to shield the other tissues from the radiation. It is left there for a period of time depending on the dosage of radiation needed and then it is removed. Although iodine brachytherapy is effective in treating melanoma of the eye, it increases the patient's risk of developing a cataract or glaucoma.
All forms of retinoblastoma and intraocular melanoma are treatable. Enucleation can usually be avoided if the tumor is found early enough. In addition, primary cancers of the eye have a relatively low mortality rate if treated promptly.
As of 2004, the National Cancer Institute is sponsoring 10 clinical trials of treatments for ocular melanoma in adults and 5 trials for treatments of retinoblastoma in children. These trials allow researchers to investigate new types of radiation therapy and chemotherapy, new drugs and drug combinations, biological therapies, ways of combining various types of treatment for eye cancer, side effect reduction, and quality of life. Information on specific clinical trials can be acquired from the National Cancer Institute at 〈http://www.nci.nih.gov〉 or (800) 4-CANCER.
Retinoblastoma is not preventable. In addition, most other types of eye tumors are thought to be partly genetic as of the early 2000s.
Brachytherapy — A type of radiation treatment for cancer in which the source of the radiation is applied directly to the surface of the body.
Carcinogen — A substance that is known to cause cancer.
Conjunctiva — The thin membrane that lines the eyelids.
Cornea — The transparent front portion of the exterior cover of the eye.
Enucleation — Surgical removal of the eyeball.
Iris (plural, irides) — The circular pigmented membrane behind the cornea of the eye that gives the eye its color. The iris surrounds a central opening called the pupil.
Ocular melanoma — A malignant tumor that arises within the structures of the eye. It is the most common eye tumor in adults.
Ophthalmology — The branch of medicine that deals with the diagnosis and treatment of eye disorders.
Orbit — The bony cavity that contains the eyeball.
Pupil — The opening in the center of the iris of the eye that allows light to enter the eye.
Uvea — The middle of the three coats of tissue surrounding the eye, comprising the choroid, iris, and ciliary body. The uvea is pigmented and well supplied with blood vessels.
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