What is ocular melanoma?

There are many different types of cancer that can affect the eye, but ocular melanoma is the most common. Melanoma is a type of cancer that develops in the cells of the body that produce melanin — the pigment that gives your skin its colour. Your eyes also have melanin-producing cells and can develop melanoma. Ocular melanoma is also known as uveal melanoma. The uvea is the middle layer of the eye beneath the white part and consists of the iris, ciliary body and choroid. Melanoma can occur any of these parts. It can also be named according to the part of the eye it started in.

Melanomas that develop on the skin usually occur on parts of the body that have been exposed to the sun. Some melanomas, however, can also start inside the eye or in a part of the body that has never been exposed to the sun.

Ocular melanoma is much rarer than skin melanoma and behaves very differently. Normally, cells multiply and die in an orderly way, so that each new cell replaces one lost. Sometimes, however, cells become abnormal and keep growing. In cancers such as ocular melanoma, the abnormal cells form a mass called a tumour. Cancerous tumours, also known as malignant tumours, have the potential to spread to other parts of the body through the blood stream or lymph vessels and form another tumour at a new site. This is known as secondary cancer or metastasis.

Most ocular melanomas develop in the part of the eye that you can’t see when looking in a mirror, so this makes ocular melanoma hard to diagnose. Ocular melanoma usually develops in any of the following three areas of the eye:

• the iris – the coloured part of the eye which helps regulate the amount of light entering the eye
• the ciliary body – the part of the eye that controls the shape of the lens and makes the fluid in the eye called aqueous humour, which provides nutrition and maintains pressure in the eye
• the choroid or posterior uvea – the vascular layer of the eye between the retina and the white outer layer (sclera).

These three areas are known as the uvea, hence the term uveal melanoma. Ocular (uveal) melanoma can occur in any of these areas, but it is more common in the choroid.

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How common is ocular (uveal) melanoma?

Ocular (uveal) melanoma is rare. Each year, around 125–150 Australians are diagnosed with this type of cancer (about 5–6 cases per million people). It is more likely to be diagnosed in men than women, and can occur at any age, but the risk increases with age.