The eye is composed of three layers. The exterior of the eyeball is a tough white fibrous layer called the sclera, which merges into the clear cornea. Inside this, there is another layer called the uvea. It is rich in blood vessels. The uvea traditionally includes three areas that are, front to back, the iris, the ciliary body and the choroid. Here is the site for many of the eye cancers. The coloured part of the eye includes the iris and the pupil that reacts to the light. The innermost layer of the eyeball is the retina. The retina is composed of cells that react to the light. They communicate with the optic nerve and ultimately the brain, allowing us to see.
Melanoma is a type of cancer that arises from melanocytes, cells specialised in the production of melanin. This is a pigment that protects our cells’ DNA from the deleterious effects of sun radiation; in the eye, melanin is thought to aid in light absorption. The most frequent melanoma in the body occurs in the skin (i.e. cutaneous melanoma). In the eye, melanoma appears in the uvea - most commonly in the choroid, followed by the ciliary body and then the iris.
Uveal melanoma is a tumour that grows and can invade the surrounding tissues. It sometimes spreads using the blood vessels to reach distant organs. Up to 50% of UM patients develop such metastases, most often in the liver. Unfortunately, uveal melanoma metastases remain very difficult, and often impossible, to treat.
Melanoma of the eye can also occur on the outermost layer of the eye, the conjunctiva, which lines the front part of the eye and the eyelid. This type of melanoma is very rare, and is called conjunctival melanoma. Despite affecting the same organ, uveal melanomas and conjunctival melanomas are very different in their nature.
Uveal melanoma is a rare intraocular tumour. Nevertheless, it is the most frequent eye cancer in adults. It has an incidence rate of 5 cases per million individuals per year and is more common in Nordic European countries. Since the early 1970s, the age-adjusted tumour incidence has remained stable. The incidence rates of this cancer vary in different countries. However, some of the differences can be attributed to different inclusion criteria and methods of calculation.
We still do not know much about the risk factors leading to this disease. Uveal melanoma seems to be more common:
Several observational studies have tried to establish a link between uveal melanoma risk and sunlight exposure. To date, only weak associations or contradictory results have been found. There is no consistent evidence that UV light exposure or other environmental agents are risk factors for uveal melanoma. This is in contrast to skin melanoma and conjunctival melanoma, where UV light exposure is a definite risk for cancer development.
Eye cancer is rare. Many eye conditions can cause symptoms that are similar to the ones described here. Nonetheless, one should always report them to a clinician - early diagnosis is very important for successful treatment.