What is ocular melanoma?
Ocular melanoma is rare, affecting approximately five in one million people; about 200 cases are diagnosed per year in Canada. Like other melanomas, it begins in melanocytes – the cells that produce the pigment melanin that colours the skin, hair, and eyes, as well as forms moles. While it represents only five per cent of melanomas, ocular melanoma is rapid and aggressive, accounting for nine per cent of melanoma deaths. Also referred to as uveal melanoma, ocular is a more inclusive term; 90 per cent of primary ocular melanoma develops in the choroid.
There are no established risk factors for ocular melanoma, but it often occurs in blue-eyed, fair-skinned people over 60 years of age. Treatment can be successful if the tumours in the eye are caught early. Around 50 per cent of tumours will metastasize, usually in two to five years. Metastasis is to the liver in approximately 90 per cent of these cases, but can also occur in the lungs, bones, brain or abdomen.
Types of melanoma of the eye
The uvea is three-layered part of the eye. It is made up of the choroid, iris and ciliary body. Uveal melanoma can form in any of these layers and is named for where it forms:
Choroidal melanoma begins in the layer of blood vessels – the choroid – beneath the retina. It is the most common type of uveal melanoma.
Iris melanoma occurs in the front, coloured part of the eye. Iris melanomas usually grow slowly and do not typically metastasize, or spread, to other parts of the body outside the eye.
Ciliary melanoma occurs in the back part of the eye – in the ciliary body. Melanomas in the ciliary body tend to grow and metastasize to the liver more quickly than iris melanomas.
The conjunctiva is the clear tissue that covers the white part of the eye, as well as the inside of the eyelids. Conjunctival melanoma is very rare. It often appears as a raised tumor and may contain little or even no pigment. Conjunctival melanoma most commonly occurs in the bulbar conjunctiva – the mucous membrane that covers the outer surface of the eyeball. Unlike other forms of ocular melanoma that spread most often to the liver, when conjunctival melanoma spreads, it most often spreads to the lungs.