Choroidal melanoma is a rare but serious eye cancer that develops in the layer of blood vessels beneath the retina, often discovered during routine eye exams before symptoms even appear.
Understanding Choroidal Melanoma
The eye is made up of three main layers. The outermost layer is the white part called the sclera, the innermost layer is the retina which senses light and helps us see, and between them lies a middle layer called the uvea. This middle layer contains blood vessels and cells that produce pigment, known as melanocytes. When these melanocytes become cancerous, they can form a tumor called melanoma. When this cancer develops specifically in the choroid, the part of the uvea at the back of the eye that supplies blood to the retina, it is called choroidal melanoma.[1][2]
Choroidal melanoma is classified as the most common primary cancer that develops inside the adult eye. However, it is important to understand that this does not mean it is common overall. In fact, it is quite rare in the general population. The word “primary” means the cancer starts in the eye itself, rather than spreading to the eye from cancer somewhere else in the body.[3][7]
The choroid plays a critical role in eye health because it supports the retina and supplies it with the blood and nutrients it needs to function properly. When cancer damages the choroid, it can significantly affect vision due to this essential supportive role. Understanding the location and function of the choroid helps explain why choroidal melanoma can cause vision problems and why treatment must be carefully planned to preserve as much eye function as possible.[1]
Epidemiology: How Common Is It and Who Gets It?
Choroidal melanoma is rare, affecting only about 5 to 10 people out of every million each year. In the United States, approximately 1,500 new cases are diagnosed annually.[2][7] While this may seem like a small number, it represents a significant population of people living with this condition. The rarity of the disease also means that not all eye care professionals encounter it frequently, which is why specialized eye cancer experts play an important role in diagnosis and care.
The disease does not affect all populations equally. Choroidal melanoma occurs more frequently in people of European descent, with incidence rates of 6 to 7.5 cases per million annually in these populations. The highest rates are seen among individuals with lighter skin tones and blue eyes. This pattern suggests that pigmentation and genetic factors play a role in who develops the disease.[3]
Choroidal melanoma is slightly more common in males than in females. Age is another important factor. While melanomas can develop at any age, most cases occur around the age of 55. Some reports suggest that the peak age range for diagnosis is between 70 and 79 years, with a median age of approximately 63 years. This means that while younger adults can develop choroidal melanoma, it becomes increasingly common as people enter middle age and beyond.[3][12]
Causes and Risk Factors
The exact cause of choroidal melanoma is not fully understood, but several risk factors have been identified. Unlike skin melanoma, where the link to sun exposure is well established, the relationship between ultraviolet radiation and choroidal melanoma is less clear. However, some evidence suggests that UV exposure may play a role. For instance, people living in Queensland, Australia, beneath the ozone hole, have the highest reported incidence of choroidal melanoma at 10 per million per year, which is twice as high as rates in the United States and Europe. This geographic pattern suggests environmental factors, particularly UV radiation, may contribute to the development of the disease.[11]
Several personal characteristics appear to increase the risk of developing choroidal melanoma. Having a fair complexion is one of the most significant risk factors. This includes having fair skin that freckles and burns easily, does not tan or tans poorly, and having blue, green, or other light-colored eyes. These physical traits suggest that melanin, the pigment that protects against UV damage, plays a protective role, and people with less melanin may be more vulnerable.[9]
Being older is another important risk factor, as the disease becomes more common with advancing age. Additionally, being White is associated with higher risk compared to other racial and ethnic groups. People who work outdoors may also face increased risk, which again points to possible UV exposure as a contributing factor. Interestingly, research has shown that these tumors are more likely to be found in the posterior, or back portion, of the eye, which receives more sun exposure.[9][11]
Symptoms: What Patients Experience
One of the challenging aspects of choroidal melanoma is that it often causes no symptoms in its early stages. Many people with small tumors feel completely normal and have no idea anything is wrong. The tumor may be discovered incidentally during a routine eye examination when the doctor dilates the pupil and looks inside the eye. In general, tumors that develop more toward the front of the eye may take even longer to cause noticeable symptoms than those in the back.[1][4]
When symptoms do occur, they can vary depending on the size and location of the tumor. Common symptoms include blurred vision, which happens when the tumor interferes with the normal function of the retina or causes fluid buildup. Some patients notice a paracentral scotoma, which is a blind spot slightly off to the side of their central vision. Others experience painless and progressive loss of peripheral or side vision.[1]
Patients may also see “floaters,” which are small spots or specks that seem to drift through the field of vision. Some people notice flashes of light. These symptoms occur when the tumor affects the retina or causes changes in the gel-like substance inside the eye called the vitreous. In rare cases, advanced choroidal melanoma can cause severe eye pain, especially if it leads to complications like glaucoma or if the tumor extends outside the eye.[1][5]
In cases where choroidal melanoma develops toward the front of the eye, there may be visible changes. These can include discoloration of the iris, a brown spot visible on the white part of the eye, an irregularly shaped pupil, or signs of glaucoma. However, these presentations are less common.[4]
It is important to remember that these symptoms can also be caused by many other, less serious eye conditions. However, if you experience any sudden changes in your vision, new floaters, flashes of light, or persistent visual problems, you should see an eye care professional promptly.[5]
Diagnosis: How Doctors Identify Choroidal Melanoma
Eye cancer specialists can correctly diagnose choroidal melanoma in over 96% to 99.6% of cases without needing a biopsy. This high accuracy rate is achieved through careful examination and specialized imaging tests. The diagnostic process typically begins with a complete eye examination, including a detailed medical history and examination of both eyes with the pupils dilated.[2][4]
During the eye exam, the doctor looks inside the eye using specialized equipment. Small choroidal melanomas typically appear as a nodular, dome-shaped, and well-defined mass under the retinal pigment epithelium, the layer of cells beneath the retina. As tumors grow larger, they may take on more irregular shapes, such as bilobular (two-lobed), multilobular (many-lobed), or even mushroom-like configurations.[1]
Choroidal melanomas can vary greatly in color. Some are darkly pigmented, appearing almost black, while others are amelanotic, meaning they have little or no pigment and appear lighter in color. Many are partially pigmented. When the tumor is light-colored, the doctor can often see abnormal blood vessels within it. The area of retina overlying the tumor usually shows changes such as small yellow deposits called drusen, patches where tissue has died, or orange discoloration.[1]
Ultrasonography, or ultrasound imaging of the eye, is one of the most valuable diagnostic tools. A-scan ultrasonography is useful for tumors thicker than 2 to 3 millimeters and can measure the tumor’s dimensions accurately. Choroidal melanoma shows a characteristic pattern on ultrasound with specific features that help distinguish it from other types of eye tumors. B-scan ultrasonography provides a two-dimensional image and is routinely used to evaluate any mass in the back of the eye.[1][3]
Doctors may also use specialized photography to document the tumor and examine blood flow within it. Fundus autofluorescence imaging can detect a substance called lipofuscin, which is a metabolic byproduct that indicates either the tumor is destroying overlying tissue or is itself degenerating. Three-dimensional optical coherence tomography (OCT) can detect even small amounts of fluid beneath the retina that may be caused by abnormal blood vessels in the tumor.[2]
Some specialists use a mnemonic device called “MOST” to help identify melanoma. The “M” stands for melanoma itself, “O” for orange pigment (lipofuscin), “S” for subretinal fluid, and “T” for thickness of the tumor. Tumors greater than 2.0 millimeters thick are more likely to be malignant.[2]
Unlike many other cancers, biopsies are usually not needed to diagnose choroidal melanoma. Biopsies require opening the eye, which carries risks of allowing cancer cells to escape, as well as risks of bleeding and infection inside the eye. However, biopsies may be performed in certain situations, such as when a tumor has an atypical appearance, when it is unclear whether the tumor is a primary melanoma or cancer that has spread from elsewhere in the body, or when the patient requests a pathology diagnosis. More recently, biopsies are sometimes done to obtain tissue for genetic testing of the tumor.[2][4]
Because the liver is the most common site where choroidal melanoma spreads, doctors typically order blood tests to check liver function in patients with this diagnosis. The most sensitive tests include measuring blood levels of alkaline phosphatase, glutamic-oxaloacetic transaminase, lactate dehydrogenase, and gamma-glutamyl transpeptidase. Additional imaging of the liver and other parts of the body may also be performed to look for any signs that the cancer has spread.[1]
Prevention: Protecting Your Eyes
While there is no guaranteed way to prevent choroidal melanoma, there are steps people can take to potentially reduce their risk. Given the possible link between UV radiation and choroidal melanoma, protecting the eyes from excessive sun exposure makes sense. Wearing sunglasses that block UV rays can serve as “sunblock for your eyes.” Look for sunglasses that block 100% of both UVA and UVB rays.[11]
People with fair skin, light-colored eyes, or those who work outdoors should be especially vigilant about eye protection. Wearing wide-brimmed hats in addition to sunglasses can provide extra protection. It is also wise to avoid artificial sources of UV radiation, such as tanning beds and sunlamps, which have been suggested as possible risk factors in some cases.[11]
Perhaps the most important preventive measure is to have regular comprehensive eye examinations. Many choroidal melanomas are discovered during routine eye exams before they cause symptoms. Early detection can lead to treatment at a stage when the tumor is smaller and vision-preserving options may be more effective. Adults should have dilated eye exams at intervals recommended by their eye care professional, which typically increases in frequency with age or if risk factors are present.[2]
Pathophysiology: What Happens in the Body
Choroidal melanoma develops when melanocytes in the uveal tract undergo malignant transformation and begin to grow uncontrollably. These pigment-producing cells are normally present in the choroid, where they contribute to the eye’s pigmentation and may play a role in absorbing stray light. When they become cancerous, they form a mass that can disrupt normal eye function in several ways.[3]
As the tumor grows, it requires an increasing blood supply to support its metabolism. Cancerous cells promote the formation of new, abnormal blood vessels through a process called neovascularization. These new vessels are often poorly formed and leaky, which causes fluid to accumulate beneath the retina. This subretinal fluid can separate the retina from its underlying support structure, leading to visual distortion or loss. The presence of subretinal fluid is one of the key signs doctors look for when diagnosing choroidal melanoma.[2]
The tumor can cause mechanical disruption of the normal eye architecture. Small tumors may remain dome-shaped and relatively contained, but as they grow, they can push against and distort surrounding structures. Large tumors may break through the overlying retinal pigment epithelium and retina, creating the characteristic mushroom shape that is sometimes seen. This breakthrough can lead to retinal detachment, where the retina pulls away from the back of the eye, causing significant vision loss.[1]
The tumor itself undergoes changes as it grows. Dead and dying cells within the tumor release lipofuscin, a yellow-orange pigmented material that can be seen on the surface overlying the tumor. This substance is a metabolic waste product that accumulates when cells break down. The presence of orange pigment is an important diagnostic clue that suggests active tumor growth and cellular turnover.[2]
In advanced cases, the tumor may grow through the wall of the eye, a process called transscleral extension. This can occur through natural channels in the sclera, such as those used by blood vessels and nerves. When tumor extends outside the eye, it may appear as a pigmented mass beneath the conjunctiva, the clear tissue covering the white of the eye. Extension beyond the eye increases the risk that cancer cells will spread to other parts of the body.[1]
Perhaps the most concerning aspect of choroidal melanoma’s pathophysiology is its potential to metastasize, or spread to distant organs. The liver is by far the most common site of metastasis. Cancer cells can enter the bloodstream and travel to the liver, where they establish secondary tumors. Even with successful treatment of the eye tumor, approximately 50% of patients with choroidal melanoma eventually develop metastases. Various factors affect the risk of metastasis, including the patient’s age, the size of the tumor, specific features seen under the microscope if a biopsy is performed, and genetic characteristics of the tumor cells.[3][12]
Understanding these pathophysiological processes helps explain why early detection and treatment are so important. Smaller tumors are less likely to have already seeded cancer cells into the bloodstream, and treating them before they cause extensive retinal damage offers the best chance of preserving vision.
