Anatomy of the eye
The eye consists of three layers covering different anatomical structures. The outermost layer, known as the fibrous coat, is composed of the cornea and sclera, which form the shape of the eye and support the deeper structures. The middle layer, known as the vascular envelope, consists of the choroid, ciliary body, and iris. The innermost is the retina, a thin multilayered membrane composed of millions of optic (nerve) cells, connective tissue, and blood vessels. The retina receives light and sends electrical impulses to the brain through a connection with the optic nerve, resulting in visualization.
The spaces of the eye are filled with a watery humour or uvea (clear watery fluid) between the cornea and the lens, and the vitreous, a jelly-like substance, behind the lens filling the entire posterior cavity.
What is melanoma?
The eye contains pigmented cells (melanocytes) in the uvea (iris, ciliary body and choroid). Thus, the uvea forms the origin of malignant melanoma of the eye. It gets its name from the point of origin as iris melanoma, choroidal melanoma and ciliary body melanoma.
Melanoma carries a risk of spreading from the eye to other parts of the body. The potential for spread is higher in larger melanomas compared with smaller tumours.
Melanoma occurs most often in the skin and less often in other parts of the body, including the eye.
Who gets melanoma and what causes it?
Ocular melanoma is the most common cancer that affects the eye. However, it is a rare disease. Worldwide, there are about 8,000 new cases of uveal melanoma per year. The average age is 60 years with a range of 6 to 100 years. The malignancy affects both men and women, with a slight predominance among men.
The etiology of uveal melanoma is still unclear. It has been established that light skin and eye colour are predisposing factors for the development of the malignancy. There is no known association with diet, stress, smoking, alcohol, or any other environmental cause. Debate continues as to whether chronic sun exposure may play a role as in cutaneous melanoma. Almost always only one eye is affected and there is no risk of cancer in family members as the disease is not hereditary.
View
The type of melanoma depends on its size and location, whether it is in the front of the eye, in the iris, or in the back of the eye, the choroid. Melanoma of the iris appears as a brown or yellow knot on the iris, sometimes with discoloration of the rest of the iris due to tumor seeds. The iris melanoma is usually visible to the patient. Melanoma of the iris can cause glaucoma and cataracts, but most patients with glaucoma or cataracts do not have melanoma. Choroidal melanoma appears as a brown or yellow tumor in the back of the eye and is not visible to the patient. Based on the thickness of the tumor, choroidal melanoma is classified as small (0-3 mm), medium (3-8 mm), and large (>8 mm). Small tumors may resemble a benign choroidal nevus or freckle.
Risk factors forsmall tumors to be categorized as melanoma include:
- Thickness > 2 mm
- Subretinal uida over the tumor
- Symptoms of ash lights, floaters or loss of vision
- Orange pigment above the tumor
- Margin of the tumor near the optic nerve disc
Medium and large choroidal melanomas can take on a dome shape or even a mushroom shape as they enlarge. Often they produce overlying subretinal uids (retinal detachment) that are associated with vision loss. Tumor growth through the eye wall into the upper soft tissues is called extraocular extension, which is worrisome.
Diagnosis
Melanoma in the eye is diagnosed during an eye examination by an ophthalmologist. Confirmation of the tumour by an ocular oncologist (eye cancer specialist) is recommended as melanoma can resemble other eye tumours. Melanoma shows typical color, shape and location, as well as several other classic features. Imaging the tumor is important to confirm these characteristics and to learn more about the tumor's blood supply.
Diagnostic imaging of the eye is a series of tests that confirm the presence of melanoma and document its size to aid in treatment.
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Enlightenment
A gentle and safe technique for directing a bright light through the wall of the eye to visualize the shadow cast by a tumor in the eye. This allows a two-dimensional view of the exact location of a peripheral tumor.
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Gonioscopy
A special mirror lens (gonioscopy lens) is placed over the anesthetized cornea and the doctor looks in depth at the structures in the corner of the front of the eye near the iris. This can provide information about the extension of the tumor into hidden areas of the eye.
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Photo
(Fundus, lamp and external)
High-resolution digital cameras are used to view structures in the front and back of the eye. They provide accurate images of the tumor, even if it is deep in the back of the eye. Images of the eye and tumor are important for documenting the tumor, its relationship to visually important structures, treatment planning, and for comparison after treatment is complete.
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Wide-angle photography of the fundus
Wide-angle contact digital camera with advanced technology to image almost the entire back of the eye.
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Fluorescein angiography (IVFA)
A test in which a yellow dye (Urescein) is injected intravenously and blue light photography is used to photograph the vessels. This test allows a better understanding of the retinal blood supply near the tumor.
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Indocyanine green angiography (ICG)
A test in which an intravenous green dye (indocyanine) is injected and red light photography is used to photograph the vessels. This test allows a better understanding of the choroidal blood supply near the tumor.
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Ultrasonography
Silent sound waves to provide a two- or three-dimensional cross-section of the back of the eye. Tumor thickness and volume is accurately measured with this method.
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Ultrasound biomicroscopy (UBM)
Silent high frequency sound waves for imaging the front of the eye.
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Optical coherence tomography (OCT)
A beam of light to measure the appearance and thickness of the retina.
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Standard scanning laser ophthalmoscopy (SLO)
A method of using light to scan the back of the eye and to photograph without a bright beam of light.
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Wide-angle scanning laser ophthalmoscopy (Optos)
Scanning laser (Optos) with advanced technology to image almost the entire back of the eye without using a bright beam of light.
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Computed tomography (CT)
A radiological test to image a cross-section of a body part using X-ray technology.
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Magnetic resonance imaging (MRI)
A radiological test to image a cross-section of a body part using magnetic technology. It is not recommended if the patient has a pacemaker or an implanted metal device such as a brain aneurysm clip.
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Positron emission tomography (PET CT)
A radiological test in which a dye is injected that attaches to cells that are actively growing and dividing, suggesting tumor cells.
Treatment:
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Objectives of treatment
The goal of treating a patient with uveal melanoma is to save the patient's life. If possible, saving the eye and vision is achieved.
Historically, the treatment modality for intraocular (inside the eye) tumors was surgery, namely enucleation (removal of the eyeball completely). Conservative treatment methods have been improved in recent decades. The choice of treatment method depends on several factors including the age and health of the patient and the size, location, thickness and growth pattern of the tumor. Treatment methods include local resection, enucleation, plaque radiotherapy, stereotactic radiotherapy and a combination of these methods.
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Local resection
Resection of uveal melanoma is a method of surgically removing the entire tumor from the eye and leaving the rest of the eye intact. This is most commonly used for melanoma of the iris or ciliary body.
The surgery is performed in an operating room and usually requires 2 to 4 hours of microscopic dissection.
After surgery, the doctor will monitor for wound leakage, cataracts, blood in the eye, retinal detachment, and other side effects. Some patients need additional radiation. Fortunately, most patients tolerate this surgery well.
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Enucleation
Before 1960, the usual treatment for choroidal melanoma was enucleation (removal of the entire eyeball). Enucleation is still used to treat some large melanomas and even some medium or small melanomas where other treatments will not work. Enucleation is done in the operating room. The eye is removed and a bead (as big as the eye) is implanted into the remaining empty orbit. The eyelids and eye muscles remain. The patient is discharged from the hospital with a bandage. After 6 weeks, the patient sees an ophthalmologist (an artist who designs artificial eyes), and the prosthesis (artificial plastic eye) is designed to match the other eye. The artificial eye is quite natural in appearance and in some cases shows a remarkable match to the healthy eye. Although the artificial eye can move, the movement is not as complete as the real eye. There is currently no surgical option for transplanting the entire eye. After enucleation, there is a reduced field of vision on the side of the artificial eye and there is some loss of depth perception. Many depth perception skills are habituated over time and most patients resume their current activities without any problem. It is recommended that protective polycarbonate lenses be worn at all times in the form of goggles during the day or glasses during activities or sports.
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Plaque radiotherapy (brachytherapy)
Brachytherapy is a type of radiation therapy that has been used to treat intraocular tumors since the 1930s. Today it is the most widely used treatment especially for choroidal melanoma. Usually brachytherapy is used with plaque in a single definitive treatment. The radiation sources used for brachytherapy are in the form of small radioactive seeds about the size of rice. These seeds are attached in a gold or steel bowl called a plate. This plate of radioactive seeds is placed on the surface of the eye, inside or near the tumor(s).
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Targeted treatment with proven efficacy
Ophthalmic plaque brachytherapy delivers a highly concentrated dose of radiation to the tumor with relatively less radiation to surrounding healthy tissue. The plaque protects other areas of the body from the radiation emitted by the seeds. This means that nearby healthy tissue is less likely to be damaged. This distinguishes plaque brachytherapy from other radiation-based treatments.
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Personalized treatment
The dose of radiation delivered to the tumor is determined by the type, number, and strength of the seeds used and the duration of the implant. The dose also depends on the size of the tumour and its location. Brachytherapy is given all the time the plaque is on the eye, usually for 2 to 4 days.
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Teamwork
Ophthalmologists and radiation oncologists work together to suture the plaque in place on the eye, with the goal of covering the base of the intraocular tumor. Plaque placement is done in an operating room. At the completion of treatment, the plaque is removed during a follow-up another surgery.
Which patients are suitable for plaque brachytherapy?
The treatment is applicable in patients with:
- Uveal melanoma
- Retinoblast
- Ocular surface tumours, including squamous cell carcinoma (SCC) and conjunctival melanoma
- Capillary hemangioma of the retina
- Vasoproliferative tumors of the retina
- Choroidal haemangioma
Results:
- Less damage to surrounding tissues
- Increased chance of:
- Preservation of eye function
- Avoiding removal of the eyeball
External beam radiotherapy/radiosurgery
While enucleation has been accepted as the standard approach to treating uveal melanomas since the 19th century, external beam radiotherapy in the form of fractionated stereotactic radiosurgery (fSRS) or SRS is one of the most commonly used nonsurgical techniques.
Forecast
Melanoma of the uvea can lead to serious, life-threatening metastasis (spread of the tumor). Overall, 20% of patients develop melanoma metastases. It is thought that metastasis usually occurs many months or years before the melanoma causes symptoms or is treated. Fortunately, most patients do not develop metastases.
Several factors suggest who is at risk of metastasis and these include the location of the tumour in the ciliary body, tumour size greater than 15 mm and tumour cell type - epithelioid, among others.
Early treatment of uveal melanoma when the tumor is small leads to prevention of metastatic spread. Several published studies have shown that plaque radiotherapy, stereotactic radiotherapy and local resection are as effective as enucleation in preventing metastasis.
Monitoring for metastases in uveal melanoma by a physician or oncologist includes:
- Physical examination (twice a year)
- Liver function tests (twice a year)
- Chest X-ray (once a year)
- Liver scan (MRI, CT or ultrasound) (once a year)
- Other proposed tests
Frequently asked questions about melanoma of the eye
- What is uveal melanoma?
This is a rare type of cancer that develops in the eyeball in a tissue called the uvea. It is subdivided into iris,ciliary body and choroidal melanoma depending on the location of the tumor.
- How common is uveal melanoma?
About 6-7 people in a million develop uveal melanoma.
- What causes uveal melanoma?
There is no known cause. This cancer in most cases is not hereditary.
- What age group does uveal melanoma cover?
All ages are at risk, but this cancer most often affects middle-aged people with a peak age of over 55. Only 1% of patients are under the age of 20.
- Does uveal melanoma impact by race?
Caucasians with fair complexions are more likely to develop uveal melanoma than African-Americans, Indians and Asians.
- Can uveal melanoma occur in both eyes?
It usually appears on only one eye.
- What condition causes a predisposition to uveal melanoma?
Patients with one blue and one brown eye are at risk for melanoma in the brown eye. This condition is called ''oculodermal melanocytosis'' or ''nevus of Ott''. Patients with dermal melanoma or dysplastic nevus syndrome have not been shown to have a higher risk of uveal melanoma, but should have their eyes examined.
- How is uveal melanoma diagnosed?
Most cases are identified by an ophthalmologist with an eye examination and then tests are used to confirm the diagnosis.
- What type of treatment is available for uveal melanoma?
Treatment varies depending on the patient and the tumor. Treatments include enucleation, plaque radiotherapy, laser photocoagulation, surgical resection or combinations of these.
- Are there different types of uveal melanoma?
There are two main cell types of melanoma. These are spindle cell and epithelioid. Most melanomas have a combination of these 2 cell types. Only if the eye is removed or the tumor is resected will it be possible to determine the cell type. Melanomas with predominantly spindle cells have thin elongated cells and suggest a better prognosis. Epithelioid-cell melanoma has round cells and suggests a worse prognosis.
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