Choroidal Melanoma - Causes, Symptoms, and Treatment

Introduction

The eye is the organ of vision. Any damage to the eye will cause severe issues as it is the most delicate organ of the body. Tumor formation is the most life-threatening condition. Malignant tumors forming in the eye structure are considered more dreadful because of their ability to spread through the optic nerve and reach the brain and other parts of the body. A choroidal layer of the eye is the most prone to tumors. Choroidal melanoma is a type of intraocular malignant tumor (the ability to spread and attack other tissues and organs) and is considered dangerous.

Structure of the Eye:

The eye is made of layers such as:

• The sclera (the white part of the eye).

• Conjunctiva (the layer that covers the sclera).

• Cornea (the transparent layer of the eye responsible for the refraction of light).

• Iris (the colored portion of the eye which is visible externally).

• Retina (the innermost layer of the eye and the image for vision is formed from here).

• Lens (the transparent structure that focuses light on the retina).

• The choroid (a thin layer present between the sclera and retina and is responsible for providing oxygen and nutrients to the eye).

What Is a Choroidal Melanoma?

Choroidal melanoma is the most common intraocular tumor and is malignant. It is a rare condition that is believed to be majorly caused by massive exposure to ultraviolet rays (UV rays). It is a type of uveal melanoma. Uvea is the structure that comprises the choroid, iris, and ciliary body.

Melanocytes are structures that produce skin pigmentation. The choroid layer contains melanocytes, and melanoma develops from these preexisting melanocytes. Choroid melanomas are darkly pigmented and have a dome-shaped structure. As the melanoma enlarges, it will break through the Bruch's membrane (innermost layer of the choroid) and take a mushroom shape. This is more commonly seen in the male population and above 55 years.

What Are the Causes of Choroidal Melanoma?

The causes believed to cause choroidal melanoma is,

• The light color of the iris.

• Large exposure to ultraviolet rays.

• Family history.

• Congenital ocular melanocytosis.

• Dysplastic nevus syndrome.

• Xeroderma pigmentosum (inherited skin disorder causing sensitivity to sunlight).

• Uveal nevus (a benign lesion that can rarely cause secondary glaucoma).

What Are the Symptoms of Choroidal Melanoma?

• A dome-shaped mass is present in the subretinal layer.

• Retinal detachment.

• Loss of vision.

• Blurred vision.

• Changes in the colored vision.

Classification of Choroidal Melanoma:

According to the size of the lesion,

• Small: 4 - 8 mm in diameter.

• Medium: 6 - 16 mm in diameter.

• Large: more than 16 mm in diameter.

According to the shape of the cells of the lesion,

• Spindle.

• Epithelioid.

• Mixed.

What Are the Possible Differential Diagnoses of Choroidal Melanoma?

• Choroidal nevus.

• Disciform scar (retinal tissue replaced by scar tissue).

• Melanocytoma.

• Metastatic carcinoma.

• Choroidal hemangioma (vascular tumor of the choroid).

• Melanocytoma.

• Hemorrhagic detachment of the choroid.

What Are the Risk Factors of Choroidal Melanoma?

• Fair complexion.

• Oculodermal melanocytosis.

• Family history of choroidal melanoma.

• Exposure to sunlight.

• Increasing age.

What Are the Complications of Choroidal Melanoma?

• Glaucoma: As the melanoma increases in size, it tends to cause glaucoma. Glaucoma causes eye pain and blurred vision.

• Loss of Vision: Large melanomas can disrupt the vision completely, causing retinal detachment. If present in the critical area of vision, even a smaller melanoma causes minimal vision loss.

How to Diagnose Choroidal Melanoma?

Patient History:

Choroidal melanomas are generally asymptomatic and are often diagnosed through a routine eye examination. The patient will be asked about the following.

• History of weight loss.

• Increased tiredness.

• Change in bowel habits.

• History of persistent cough.

• Severe pain is experienced while choroidal melanoma impinges on adjacent structures.

Diagnostic Tests:

• Slit Lamp Biomicroscopy: A microscope is fitted with a slit lamp attached, and the patient will be asked to sit opposite to that. The eyes of the patient can be focussed using the slit lamp, and any irregularities or injuries can be studied clearly.

This test is used to assess the anterior involvement of the tumor.

Additionally, this slit lamp will be attached with a gonioscopy to visualize the tumor.

• Indirect Ophthalmoscopy: Using this test, the inside layer of the back of the eye can be studied. This is considered the standard gold test for diagnosis as a three-dimensional view of the tumor can be studied.

• Fluorescein Angiogram: This test includes a special dye and a camera to assess the blood flow in the choroidal layer. In the case of spreading through the Bruch membrane, double circulation of blood will be noticed both in the retina and the choroid.

• Positron Emission Tomography (PET Scan): This test is done to assess the biochemical functions of the tissues and organs of the body. In this case, the spread of a tumor to the liver can be detected.

• Collaborative Ocular Melanoma Study (Coms): This test detects choroidal melanoma with 99 % accuracy.

• Computed Tomography (CT Scan) and Magnetic Resonance Imaging (MRI) is also used to detect choroidal melanoma.

• Optical Coherence Tomography: This test is non-invasive imaging, where light waves are used to record images of the layers of the eye. It is used to detect choroidal lesions that are hyperreflective. The presence of a subretinal fluid can also be detected.

In difficult-to-diagnose cases, fine-needle aspiration biopsy is needed.

How to Treat Choroidal Melanoma?

Treatment options include,

• Enucleation: This is the classic approach to treating choroidal melanoma, especially in cases where vision is significantly compromised, and none of the other techniques seem to show good results.

• Plaque Brachytherapy: Medium-sized choroidal melanomas are destroyed using plaque brachytherapy. The DNA of the cancerous cells is destroyed using radiation.

• Laser Photocoagulation: It is a type of laser surgery used to destroy cancer cells through a beam of light.

• Block Excision: Block excision is found to improve vision. The tumor structure and the 3 mm of healthy tissue surrounding the tumor will be removed.

Small-Sized Choroidal Melanoma - During the first visit, the doctor will ask the patient to wait for some time to assess the growth of the tumor. Then, with proper documentation of the growth and spread, definite treatment can be given.

How Is the Prognosis of Choroidal Melanoma?

Prognosis depends on the size and location of the tumor. Tumors of spindle cells show a better prognosis than the epithelioid ones. If the eye's ciliary body is involved, the prognosis can be bad. Prognosis is found to be worse in the case of liver metastasis.

Conclusion

Choroidal melanoma is a rare condition but causes severe damage if it occurs. Not exposing ourselves to the sunlight too much is the only aspect that could be prevented, whereas other causes are difficult to control. The developing medical technologies and discovery of new medicines to cure tumors have increased hope in terms of prognosis. Seeing a doctor immediately once it starts showing a sign will help prevent further complications.