Choroid Melanoma

Choroid melanoma is the most common cancer that develops inside the adult eye, yet it remains a rare condition that often goes unnoticed until detected during a routine eye examination.

Table of contents

• What Is Choroid Melanoma
• Who Gets Choroid Melanoma
• Signs and Symptoms
• How It Is Diagnosed
• Associated Anatomy

What Is Choroid Melanoma

Choroid melanoma is a primary cancer of the eye that develops from pigment-producing cells called melanocytes in the choroid, which is the middle layer of the eye wall^[1][2]. The eye wall consists of three main layers: the white outer layer called the sclera, the middle vascular layer called the uvea, and the inner retinal layer^[2]. The uvea itself includes the iris (the colored part of the eye), the ciliary body, and the choroid^[3].

The choroid is a critical vascular layer that sits between the sclera and the retina, supplying blood and nutrients to the eye^[1][3]. Because melanocytes are primarily found in this uveal layer, cancers that develop from these cells are called choroidal melanomas when they occur in the choroid^[2]. This type of cancer is also referred to as uveal melanoma when it affects any part of the uvea, or intraocular melanoma, meaning melanoma inside the eye^[5][9].

ocular melanoma, uveal melanoma, intraocular melanoma

Choroidal melanoma represents the largest portion of uveal melanomas, accounting for approximately 90% of cases, while 5 to 8% originate in the ciliary body and 3 to 5% in the iris^[3]. Although it is the most common primary cancer of the eye in adults, it remains rare overall, representing 3 to 5% of all melanomas in the body^[3].

Who Gets Choroid Melanoma

Choroidal melanoma is a rare cancer, with only 5 to 10 out of each million people diagnosed each year^[2]. The incidence is estimated at 6 to 7.5 cases per million annually in populations of European descent^[3]. Approximately 1,500 new cases of choroidal melanoma are diagnosed in the United States each year^[7].

The disease shows clear patterns related to certain characteristics. It is more common in people with blue eyes and lighter skin^[3]. The condition is slightly more common in males than females^[3]. While melanomas can arise at any age, most cases occur around age 55, with the peak age for diagnosis ranging from 70 to 79 years and a median age of diagnosis around 63 years^[3].

Research suggests a possible connection between ultraviolet radiation exposure and choroidal melanoma. People living in Queensland, Australia, beneath the ozone hole have the highest reported incidence at 10 per million per year, which is twice the rate seen in the United States and Europe^[11]. Additional support for this connection comes from the greater frequency of these tumors in patients with blue eyes, those with outdoor occupations, and the tendency for tumors to be found in the posterior, more sun-exposed part of the eye^[11].

Signs and Symptoms

Many people with choroidal melanoma have no symptoms at all, and the cancer is often discovered during a routine eye examination^[4]. Choroidal melanomas can remain asymptomatic for prolonged periods of time and may be found incidentally during ophthalmoscopy, which is an examination that allows doctors to look inside the eye^[1]. In general, the more forward in the eye the tumor originates, the longer it takes before any symptoms appear^[1].

When symptoms do occur, they may include seeing flashes of light, distortion or loss of vision, and floating objects in the vision^[4][12]. Other symptoms can include blurred vision, a dark spot growing in the colored part of the eye, painless and progressive loss of side vision, and floaters^[1][3]. Some patients may experience a change in the shape of the pupil or poor vision in one eye^[5].

During an eye examination, doctors may observe specific features of choroidal melanoma. Small tumors typically appear as a nodular, dome-shaped, and well-defined mass under the retinal pigment epithelium, which is a layer of cells at the back of the eye^[1]. As the tumors grow larger, they may take on irregular shapes such as bilobular, multilobular, or mushroom configurations^[1].

The tumors can vary in color, ranging from having no pigmentation at all to being darkly pigmented, and some are partially pigmented^[1]. When the tumor is light-colored, its abnormal blood vessels can usually be seen during examination^[1]. Above the melanoma, there are typically changes in the retinal pigment layer, including areas of breakdown and an orange discoloration, though these orange changes can occur in both cancerous and non-cancerous lesions^[1].

Less common presentations can include severe eye pain, a painful blind eye with cataract, and bulging of the eye from the tumor extending through the wall of the eye^[1]. Tumors located toward the front of the eye might show enlarged blood vessels visible through the clear covering of the eye, or a small area of abnormal darkening visible on the outside of the eye^[1].

How It Is Diagnosed

Eye cancer specialists can correctly diagnose an intraocular choroidal melanoma in over 96% of cases without needing a biopsy^[4]. In fact, in the Collaborative Ocular Melanoma Study, participating eye cancer specialists correctly diagnosed select choroidal melanoma in over 99.6% of cases without a biopsy^[2]. The tumor is most often diagnosed through a complete eye examination with testing^[2].

The diagnostic process includes asking questions about medical history, examining both eyes, and looking into the eye through a dilated pupil^[2][5]. During the eye exam, healthcare professionals may first examine the outside of the eye, looking for enlarged blood vessels that might indicate something concerning is happening inside^[10]. They then look inside the eye using special equipment with lenses and bright lights^[10].

Several imaging tests are commonly used to support the diagnosis. Ultrasonography, which uses sound waves to create images, is considered one of the most valued diagnostic tests^[3]. A-scan ultrasonography is useful for tumors thicker than 2 to 3 millimeters and shows characteristic patterns with choroidal melanoma^[1]. B-scan ultrasonography is a routine test used in evaluating any mass at the back of the eye^[1].

Specialized photography is also important for diagnosis. Fundus photography takes color pictures of the inside surface of the eye and can show an eye melanoma^[10]. Different types of imaging can examine the blood circulation within the melanoma^[2]. Optical coherence tomography, which creates three-dimensional images, can detect small amounts of fluid under the retina^[2].

One helpful tool for diagnosis is a mnemonic device called “MOST” that helps eye care specialists determine if a tumor is a melanoma^[2]. The “M” stands for melanoma, “O” for orange pigment, which is a breakdown product that indicates the tumor is destroying overlying tissue, “S” for fluid under the retina created by abnormal blood vessels in the tumor, and “T” for thickness, as tumors greater than 2.0 millimeters are more likely to be cancerous^[2].

Although biopsies are occasionally necessary, they are usually avoided because they require opening the eye, which risks letting melanoma cells escape, and they carry risks of bleeding inside the eye and infection^[4]. Biopsies may be performed for unusual-appearing tumors, when a tumor that spread from elsewhere in the body is suspected and no primary cancer has been found, or when a patient requests confirmation through tissue examination^[2].

Blood tests to check liver function are indicated for any patient with uveal melanoma because the liver is the most common site where choroidal melanoma spreads^[1]. The most sensitive tests include measuring blood levels of alkaline phosphatase, glutamic-oxaloacetic transaminase, lactate dehydrogenase, and gamma-glutamyl transpeptidase^[1].

Associated Anatomy

• Choroid
• Uvea
• Iris
• Ciliary body
• Retina
• Sclera
• Cornea
• Retinal pigment epithelium