What Is Eye Melanoma (Ocular Melanoma)? What Causes Eye Melanoma?

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Main Category: Eye Health / Blindness
Also Included In: Cancer / Oncology
Article Date: 29 Mar 2010 - 0:00 PDT

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Ocular melanoma, also known as melanoma of the eye or uveal melanoma is the most common type of eye cancer. Tumors arise from the melanocytes - pigment-producing cells - that reside within the uvea, giving color to the eye. Most melanomas grow in the skin, but some can develop in other parts of the body, including the eye.

According to the National Health Service (NHS), UK, approximately 500 new cases of ocular melanoma are diagnosed in the UK annually, making it a rare condition. Most patients are diagnosed in the 50s.

According to the American Cancer Society:

• Approximately 2,350 new cases of cancer of the eye and orbit in 2009 were diagnosed in the USA.
• Most of these were cases of melanoma.
• 230 people died from cancer of the eye in 2009 in the USA.
• The incidence of eye melanomas has been fairly stable over the last 25 years.
• Secondary eye cancers are more common than primary eye cancers.
• 90% of melanomas start in the skin, while most cases of lymphoma start in lymph nodes.

If the cancer starts off in the eye it is known as primary eye cancer. If the eye melanoma started off elsewhere in the body, it is called secondary eye cancer.

Orbit - this consists of the tissues surrounding the eyeball, including muscles that make the globe move in different directions, as well as nerves attached to the eye. Orbital cancers are cancers of these tissues.

Treatment for eye melanoma is effective if it is detected and treated early enough. According to the Mayo Clinic, USA, 84% of patients diagnosed with early-stage melanoma survive for at least five years.

What are the signs and symptoms of eye melanoma (ocular melanoma)?

A symptom is something the patient senses and describes, while a sign is something other people, such as the doctor notice. For example, drowsiness may be a symptom while dilated pupils may be a sign.

Some patients may experience no symptoms, while others may have light flashes, blurring of vision, or see dark spots in their field of vision. The following signs and symptoms are possible:

• A dark spot in the iris (which grows)
• A displacement of the eye within the eye socket
• Blurry vision in one eye
• Floaters - small specks or squiggles that move about in the patient's field of vision. They may be seen more clearly when looking at a plain background, such as a blank wall. They may appear as tiny dots, circles, lines, clouds or cobwebs.
• Loss of peripheral vision in one eye
• Pain in or around the eye (rare with eye cancer)
• Poor vision in one eye
• Seeing flashing lights
• Watery eyes

What are the risk factors for eye melanoma (ocular melanoma)?

A risk factor is something which increases the likelihood of developing a condition or disease. For example, obesity significantly raises the risk of developing diabetes type 2. Therefore, obesity is a risk factor for diabetes type 2. Risk factors for eye melanoma include:

• Eye color - people with blue eyes have a higher risk of developing melanoma of the eye compared to individuals with brown eyes.
• Genetics - some chromosomal abnormalities, such as those found on chromosome 3, increase the risk of melanoma spreading from the eye to other parts of the body.
• Dysplastic nevus syndrome - a condition in which the person develops atypical moles (dysplastic nevi) whose appearance is different from ordinary moles. The moles have more irregular borders, are frequently mixed in color, and appear in clusters. Dysplastic nevi are more likely to develop into malignant melanoma than ordinary moles.
• Exposure to ultraviolet light - although not conclusively proved, experts believe that exposure to ultraviolet light (sun exposure) increases the risk of developing eye melanoma.

What are the causes of eye melanoma (ocular melanoma)?

Experts are not sure what the exact cause of ocular melanoma is. Most agree that genetics (DNA) plays a role in making cells become cancerous.

What are genes, DNA and chromosomes? Every living organism has genes. Genes are a set of instructions that decide what the organism is like, how it survives, and how it behaves in its environment. The genes lie in long strands of DNA (deoxyribonucleic acid) called chromosomes. Humans have 23 pairs of chromosomes - or a total of 46. A donkey has 31 pairs of chromosomes, a hedgehog has 44, and a fruit fly has just 4.

A gene consists of a long combination of four different nucleotide bases (chemicals). There are many possible combinations. The four nucleotides are:

A (adenine)
C (cytosine)
G (guanine)
T (thymine)

Different combinations of the letters ACGT give people different characteristics. For example, a person with the following combination - AAACCGGTTTTT - may have green eyes, while somebody whose combination is - AAACCGGTTTAA - may have blue eyes. In fact, the last two letters - TT - and - AA - mean the color, and the first ten letters - AAACCGGTTT - mean the eye. (this gene formula is a simplification; in reality they would be much longer).

To recap:

• Genes carry the codes ACGT. We have thousands of genes. They are like our computer program and make each one of us what we are. A gene is a tiny section of a long DNA double helix molecule, which consists of a linear sequence of base pairs. A gene is any section along the DNA that has instructions encoded that allow a cell to produce a specific product - usually, a protein, such as an enzyme - that triggers one precise action. There are between 50,000 and 100,000 genes, and every single gene is made up of thousands, even hundreds of thousands, of chemical bases.
• Chromosomes are the long strands of DNA. They are organized structures of DNA and protein and are found in cells. Humans have 23 pairs of chromosomes. An enormous number of genes lie in each chromosome strand. Scientists say that a chromosome is a single piece of DNA which has many genes, regulatory elements and other nucleotide sequences (sequences of the letters ACGT).
  
  A chromosome consists of DNA and has proteins attached to it. These chromosomes are located in your body's cells, which then contain this important genetic information held in the long strands of DNA.
• DNA (deoxyribonucleic acid) is the chemical that appears in strands (see picture - below right). Every cell in your body has the same DNA. Each person's DNA is different - this is what makes each of us unique. DNA is made up of two long-paired strands spiraled into the famous double helix. Each strand contains millions of chemical building blocks called bases. Defects (mutations) in DNA can cause cells to malfunction, sometimes resulting in cancer. These mutations may be either inherited or acquired during life.

Links have been found between eye cancer and some genetic changes. However, scientists have not yet been able to determine where exactly these changes occur, or whether they actually cause cancer to develop.

Ocular melanoma occurs most frequently in the vascular layer of the eye between the retina and the white of the eye - this part of the eye is called the uvea.

Diagnosing eye melanoma (ocular melanoma)

Early detection and treatment for ocular melanoma is crucial for effective treatment. Having regular eye tests with an ophthalmologist (eye doctor) is the best way to protect your eyes.

The doctor examines the outer part of the eye, looking out for enlarged blood vessels, which may indicate a number of eye conditions, including a tumor. The ophthalmologist also examines the inside of the eye in two possible ways:

Ophthalmoscopy - this is an examination of the interior of the eye, including the retina, optic nerve and lens. This may be done by indirect ophthalmoscopy or direct ophthalmoscopy.

• Indirect ophthalmoscopy - a head lamp is used to shine a very bright light into the eye.
• Direct ophthalmoscopy - an ophthalmoscope, a device consisting of a concave mirror and battery-operated light is used. The operator uses a single monocular eyepiece to look into the eye. The device has a rotating disc of lenses which lets the examiner observe at various depths and magnifications. The patient may be given medication that dilates the pupils and enlarges the opening into the structures within the eye.

In the majority of cases tumors and other abnormalities can be detected and diagnosed just by looking inside the eye. The following imaging tests may also be ordered if the doctor suspects the patient may have eye melanoma:

• Ultrasound - a transducer, a wand-like device, uses high-frequency sound waves which can produces images of structures inside the eye. Eye melanomas usually have distinctive features on the ultrasound images, making this procedure especially useful in the detection and evaluation of eye tumors. The doctor may also be able to determine the thickness of the tumor. Ultrasound may be used later on to see how effective treatment has been.
• Flourescein angiography - a yellow dye is injected into a vein in the patient's arm. As the dye circulates in the eyes, a special camera takes flash pictures every few seconds for several minutes. The images can tell the doctor where the dye is going, highlighting the blood vessels in the retina.

Metastasis - the doctor may also want to know whether the cancer has metastasized (spread to other parts of the body), such as the lungs or liver. The following tests may be ordered:

• Blood tests - these may determine whether the cancer has spread to the liver.
• Chest X-ray - to determine whether the cancer has spread to the lungs.
• CT (computerized tomography) scan - a medical imaging method that employs tomography. Tomography is the process of generating a two-dimensional image of a slice or section through a 3-dimensional object (a tomogram). The medical device (the machine) is called a CTG scanner; it is a large machine and uses X-rays to generate a 3-dimensional (3-D) image of the inside of an object.
• MRI (magnetic resonance imaging) scan - uses a magnetic field and radio waves to create detailed images of the body.

Biopsy - this is a tissue sample. If the doctor is not sure whether the tumor is a melanoma a biopsy may be taken. A small sample of the tumor is surgically removed and then evaluated in the laboratory. In most cases biopsies are not needed.

What are the treatment options for eye melanoma (ocular melanoma)?

Treatment options depend on several factors, including where the tumor is, its size, the patient's general health, and cytogenetics. Cytogenetics is cytology (study of cells) with the study of genetics - which in this case means the genetics of the tumor.

As ocular melanomas are very rare the patient should perhaps consider getting a second opinion. It is important to have a doctor experienced in treating this kind of cancer.

Watchful waiting - if there is a small lesion, some doctors may recommend not treating straight away, but just monitoring things closely.

If the melanoma is medium- or large-sized the doctor will most likely recommend treatment.

Even though every effort is made to protect the patient's vision, destroying a melanoma does frequently result in some loss of vision. As eye cancers may eventually result in the death of the patient, some treatment will result in the loss of vision in the affected eye.

Surgery - the following surgical procedures may be recommended:

• Iridectomy - parts of the iris with small melanomas, which have not spread to other parts of the eye, are removed.
• Iridotrabeculectomy - parts of the iris are removed, as well as the supporting tissues where melanomas may have spread to.
• Iridocyclectomy - part of the iris and ciliary body are removed. The ciliary body is a thin, blood vessel-filled middle layer of the eye, situated between the white of the eye (sclera) and the retina.
• Choroidectomy - part of the choroid is surgically removed. Sometimes part of the wall of the eye is also removed. Sometimes radiation therapy is used after the operation.
• Enucleation - the whole eye is surgically removed. If the tumor is large and any other treatment would result in the loss of most of the eye, the surgeon may recommend enucleation. This procedure may also be recommended if the patient is experiencing eye pain. An ocular prosthesis (artificial eye) is implanted to substitute the real eye - the prosthesis does not restore vision at all, it is a cosmetic substitute.

Radiotherapy (radiation therapy) - radiation can damage cells by destroying their genetic material, blocking the reproduction of cells. The radiation is carefully targeted so that cancerous cells are damaged, with as little damage as possible to healthy cells. Radiotherapy is usually used for medium to large sized tumors. However, it may sometimes be used for small tumors as well.

• Teletherapy - the radiation is generated outside of the patient's body and directed into the eye.
• Brachytherapy - small radioactive seeds are temporarily anchored into the eye. A plaque (small implant) containing several iodine 125 (radioactive) seeds is stitched to the wall of the eye, near the tumor. The plaque remains there for four to five days. The doctor carefully monitors the size of the tumor, which hopefully would have shrunk.

Small melanomas:

• Radiation therapy may be used sometimes to treat small eye melanomas.
• TTT (transpupillary thermotherapy) is a type of infrared laser therapy uses heat in the form of a laser to shrink smaller tumors.
• Cryotherapy, which freezes the cancerous cells, may also be used. Sometimes surgeons may use a combination.

Written by Christian Nordqvist
Copyright: Medical News Today
Not to be reproduced without permission of Medical News Today

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