Introduction
Iris melanomas are primary malignant neoplasms of the iris. The tumor of the iris accounts for 5 % of uveal tumors. The eye's iris is the colored part or segment of the ocular anatomy that primarily helps control the amount of light entering the eyes by altering the size of the pupil. The Iris’s color depends on the amount of melanin pigment present in the superficial layer of the iris.
What Is the Anatomical Structure of the Iris of the Eye?
The iris of the eye consists of two components;
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The superficial or the front part comprises the pigmented fibrovascular tissue.
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The deeper part of the stroma comprises pigmented epithelial cells.
What Is Melanoma?
Melanoma is a form of skin cancer that involves melanocytes or cells that produce melanin. Melanin is the pigment that gives color to the skin. It can affect various anatomical parts of the body, including the eyes, nose, and throat.
What Causes Iris Melanoma?
Iris melanoma of the eye is primarily due to nevi (malignant growth of the melanocytes or melanin-producing cells). However, they can also occur de novo. The transformation of iris nevi to iris melanomas increases from 4 % in ten years to 11 % in 20 years.
Can Ultraviolet Rays Increase the Risk of Iris Melanomas?
Several studies have a positive association between ultraviolet (UV) B rays and iris melanomas of the eyes. However, apart from the UV rays, several other factors aggravate the possibility of iris melanomas formation. The risk factors include:
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Chromosomal aberrations.
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Lighter skin.
What Is the Prevalence of Iris Melanomas?
Iris melanomas most commonly occur in the fifth decade of life. Although melanomas do not show any gender predilection; however, there exists a racial preference for the condition. Caucasians are more prone to contracting iris melanoma compared to other races.
What Are the Clinical Features of Iris Melanoma?
Patients suffering from iris melanoma mostly remain asymptomatic. However, there might be a sudden rapid growth of the tissue. Other features that are seen in patients suffering from the disease are:
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The presence of mass inside the iris.
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Heterochromia (a condition in which the color of both eyes is different).
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Chronic uveitis (inflammation of the uvea).
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Glaucoma (a state that is characterized by damage to the optic nerve due to increased intraocular pressure).
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Hyphema (a condition characterized by the accumulation of blood in the anterior chamber of the eye). Hyphema is spontaneous in this condition.
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Pain due to an increase in intraocular pressure.
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Formation of cataract (opacification of the lens).
What Are the Different Types of Iris Melanomas?
Iris melanomas can be classified into three categories based on their clinical presentations;
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Circumscribed: In circumscribed iris melanoma, there is the presence of a well-defined pigmented mass in the lower half of the iris stroma.
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Diffuse: There is complete discoloration of the iris followed by iris crypts and pigmentation of the eye's anterior chamber. They are primarily unilateral and can lead to disc cupping and vision loss.
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Tapioca: Tapioca melanoma presents multiple amelanotic nodules all over the surface. The presence of amelanotic nodules gives the appearance of a "tapioca pudding."
The variation in pigmentation is an indication of malignancy.
How Is Iris Melanoma Diagnosed?
Patients with iris melanoma are asymptomatic; hence the diagnosis of the state occurs during the routine clinical examination of the patient. Other methods that aid in diagnosing the condition is:
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Clinical photos- They also can be used as a reference to monitor the growth of the disease during follow-ups.
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Ultrasonography- Iris melanomas, when observed using ultrasound biomicroscopy, give a "lion's paw" appearance due to anterior and posteriorly extension of the lesion.
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B-scan ultrasonography helps evaluate the extent of the lesion, especially larger lesions.
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Histological examination of the biopsy tissue reveals cells with varying levels of pigmentation and vascularity.
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Imaging like anterior segment optical coherence tomography helps visualize smaller lesions with precision.
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Genetic profiling following a biopsy is also performed.
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Fine needle aspiration is recommended in suspected cases of myeloma.
What Are the Clinical Criteria Used for Diagnosing Iris Melanomas?
Shield gave the clinical criteria chiefly used while diagnosing iris melanomas. It states that a lesion can be diagnosed as iris melanoma if it fulfills the following criteria:
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The lesion is more than 3 mm in diameter and 1 mm thick.
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It completely replaces the iris stroma.
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No less than three of the following characteristics must be present:
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Growth.
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Secondary glaucoma.
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Secondary cataract.
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Prominent blood vessels.
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Ectropion iridis (presence of pigmented epithelium on the anterior surface of the iris).
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How Are Patients With Iris Melanomas Managed?
Smaller lesions and non-growing lesions do not require any treatment. However, they must be monitored regularly to look for any growth, surface irregularity, increased vascularization, nodules, and fr any associated hyphema. The various treatment options include -
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Tebentafuspis the first T-cell receptor drug approved for treating metastatic or unresectable uveal tumors.
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Brachytherapy. Plaque radiation therapy is given with palladium (103) isotope.
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Proton-beam irradiation of the tissue.
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Excision of the lesion.
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Enucleation.
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Enucleation is performed in severe or diffuse cases involving the angle of the eye and in case of other related complications.
Regular follow-up every six months for patients with iris melanoma is necessary to monitor the growth pattern of the condition.
The conditions must be ruled out before forming a confirmed diagnosis of iris melanoma. The diseases that are similar to iris melanoma are:
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Iris freckle.
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Iris nevus syndrome.
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Leukemia.
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Iris foreign body.
Can Iris Melanomas Cause Any Further Complications?
Iris melanomas, if left untreated, can cause several other complications, such as:
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Secondary glaucoma.
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Neovascular glaucoma.
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Inflammatory posterior synechiae.
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Pupillary distortion.
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Metastases.
Can Iris Melanomas Transform Into Malignancy?
Iris melanomas have a lower ability to metastasize compared to ciliary and choroidal tumors. The rate of metastasis ranges from 3 % to 10 % within five to twenty years. The factors that predispose melanomas to malignancies are:
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Old age.
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Glaucoma and increase in intraocular pressure.
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Extension of the tumor into the angle and extraocularly.
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Recurrence following surgery.
Is Iris Melanoma a Severe Condition?
Iris melanomas are mostly indolent with a shallow rate of metastasis. As a result, melanomas usually have a good prognosis.
Conclusion
Iris melanomas are malignant tumors of the iris of the eye. They occur due to iris nevi. Patients with iris melanomas are asymptomatic and diagnosed by imaging and diagnostic modalities. Smaller melanomas require no treatment; larger lesions may require radiotherapy or surgical intervention. Overall, iris melanomas have a good prognosis.
