Malignant melanomas do usually develop in the skin but occasionally they can start in the eye. Malignant melanomas which start in the eye are called ocular melanomas.

There are about 350 new cases of ocular melanoma each year in the UK.

The eyeball is made up of three layers, or coats. The outer fibrous coat is called the sclera and the in the inner coat is the light-sensitive retina. The middle coat contains blood vessels and muscles and is made up of three parts. These are:

• the iris. This is at the front of the eye and is the ring around the pupil that gives our eyes their colour.
• the ciliary bodies. These lie either side of the iris and are made up mainly of muscle fibres.
• the choroid. This forms the rest of the middle layer of the eyeball and is made up mainly of blood vessels.

About 8 out 10 malignant melanomas of the eye develop in the choroid and most of the others start either in the ciliary body or iris. Rarely other parts of the eye may be affected.

Ocular melanomas can occur at any time of life but are most frequent in late middle age.

Unlike melanomas of the skin, sunlight does not seem to be a factor in causing ocular melanomas.  Perhaps for this reason ocular melanomas are not becoming more common, whereas the numbers of cutaneous (skin) melanomas is increasing quite dramatically.

Ocular melanomas can spread to other parts of the body. The eye is unusual in that it has no lymph vessels, so melanomas of the eye do not go to the lymph nodes, but they can send cancerous cells through the blood stream. These most commonly go to the liver and form secondary cancers (metastases) there. Very often these secondary cancers only appear many years after the original, primary, cancer in the eye.

Years ago the treatment for ocular melanomas was always complete removal of the eyeball (an operation called enucleation). Occasionally enucleation is still done for some large ocular melanomas but a range of other treatments are available including:

• laser treatment. This uses a laser beam to ‘burn out’ the melanoma. This is usually only suitable for small tumours.
• scleral plaque radiotherapy. This uses tiny amounts of radioactive material, sealed in gold or silver plaques, which are stitched to the surface of the melanoma.
• proton beam therapy. This is a very special type of radiotherapy that uses a machine called a cyclotron to produce a very precise beam of radiation that can be focused on the melanoma without causing much damage to the rest of the eye.
• choroidal resection. This is an operation to take away just that part of the lining of the eye that is affected by the tumour, leaving the rest of the eyeball intact and partially sparing the sight.

The choice of treatment depends on the position and size of the tumour and is tailored to meet the needs of the individual.

The outlook for melanomas of the iris is very good, with a very high cure rate (probably because their position, at the front of the eye, means that these tumours are usually discovered at an early stage). For ocular melanomas arising in other parts of the eye the outlook is still good with most people being cured.

The main thing that influences the chance of a cure with ocular melanomas is their size. In general the larger the melanoma the greater the chance that it might have sent off cells to form secondary cancers in the liver or elsewhere.