The word 'tumour' merely means a lump, which may be a growth or another kind of mass, such as a blood clot or cyst.

A neoplastic tumour is a growth consisting of abnormal, new tissue. This can be benign or malignant. A benign tumour damages the eye without posing any threat to life. A malignant tumour can be lethal because of spread to vital tissues around the eye and dissemination to other parts of the body (i.e., metastasis).

Adenoma and adenocarcinoma
These are very rare tumours arising from particular membranes inside the eye (i.e., retinal pigment epithelium and ciliary epithelium). They can be benign or malignant. If malignant, they can invade local tissues within and around the eye but do not usually spread to other parts of the body.

Congenital hypertrophy of the retinal pigment epithelium
This lesion, which is also called 'chirpy', is a flat birthmark at the back of the eye. It is a large, dark, black spot, typically with a few white spots and discrete edges, often surrounded by a white 'halo'. Despite its striking appearance, it is entirely harmless and does not require any treatment. CHRPE Cyst A hollow swelling, filled with fluid. This tends to arise behind the iris, pushing the iris forwards. Intraocular cysts are not usually neoplastic and do not threaten life.

Disciform lesion
This is a collection of fresh blood, clotted blood and scar tissue beneath the retina. It usually arises in more elderly individuals and is caused by abnormal veins growing beneath the retina.

Haemangioma
This is a benign tumour consisting of abnormal blood vessels. Fluid leaking from the tumour collects beneath the retina, causing distorted vision and blurred vision. If the amount of fluid beneath the retina is excessive and if the retina becomes totally detached, then abnormal blood vessels can develop on the iris. These can block the outflow of fluid from the eye to cause an increase in pressure, which can be painful.

Choroidal haemangioma
The circumscribed variety usually becomes noticeable in middle age. A diffuse variety occurs in younger patients as part of the Sturge Weber Syndrome, which is characterized by a red birthmark on the skin of the face.

Leiomyoma
A very rare benign tumour consisting of muscle.

Melanoma
This is a malignant tumour arising from melanocytes. Intraocular melanoma develops within the choroid, ciliary body or iris. Extraocular melanoma develops in conjunctiva or skin.

Iris melanoma
Intraocular (or 'uveal') melanomas affect about one person in every 2500 whereas conjunctival melanomas affect one person in every 125,000. Both tumours tend to affect adults. The cause is unknown, although as with skin melanomas, ocular melanomas tend to be more common in individuals with fair skin, light-coloured eyes, and a tendency to sunburn.

Choroidal melanoma tends to:

• Cause retinal detachment, with blurred vision, distorted vision, flashes of light and a visual field defect;
• Perforate the retina, to cause vitreous haemorrhage (i.e., bleeding into the jelly), with floaters and blurred vision;
• Grow through the sclera (i.e., wall of the eye) to invade the tissues around the eye.

Ciliary body melanoma tends to:

• Press on the lens, to displace and distort the lens, which also becomes cataractous (i.e., cloudy) to cause distorted vision and blurred vision.
• Invade the iris to become visible to the naked eye;
• Invade the gutter draining fluid from the eye (i.e., trabecular meshwork in angle of anterior chamber) to cause raised intraocular pressure and loss of vision (i.e., secondary glaucoma).
• Spread to tissues around the eye.

Ciliary body tumour Iris melanomas tend to:

• Press on the lens to cause cataract;
• Invade the angle to cause glaucoma.

Conjunctival melanoma tends to:

• Form a nodule in the transparent conjunctiva over the white of the eye or on the inner surface of the eyelid;
• Spread in a diffuse fashion in the conjunctiva;
• Scatter tumour cells to glands in the cheek and neck, where new tumours may develop;
• Form new tumours in other parts of the body.

Sooner or later, melanomas develop the capacity to scatter malignant cells to distant parts of the body, particularly the liver. This process is called metastasis. Intraocular melanomas metastasize via the blood circulation whereas conjunctival melanomas can also spread through the lymphatic system.

With intraocular melanomas, the chances of metastasis depend on:

• The size of the tumour;
• Transformation of tumour cell shape from spindle (i.e., spiky) to epithelioid (i.e., round);
• The formation of circular membranes within the tumour (i.e., closed loops);
• The loss of inhibitory controlling genes within the tumour, particularly those on chromosome 3;
• Tumour spread outside the eye;
• Tumour recurrence after radiotherapy or resection.

With extraocular melanomas, the chances of metastasis depend on features such as:

• The thickness of the tumour;
• Location in the fornix (i.e., where the eye meets the eyelid).

Tumour recurrence after radiotherapy or resection is unlikely to be the cause of metastatic disease but probably indicates that the original tumour was relatively aggressive.

Most patients with ocular melanoma have a good prognosis for survival when first seen and treated.

Metastasis
This is a malignant tumour spreading via the blood circulation to the eye from a cancer in another part of the body, such breast or lung.

This tumour is usually yellow or white. It grows rapidly and leaks large amounts of fluid to cause progressive loss of vision. It usually responds to a small dose of external beam radiotherapy, with improvement in vision.

Naevus (plural: naevi)
This is a benign 'mole' arising from melanocytes. It forms a grey, brown or yellow lump, either in the choroid, beneath the retina, or on the iris. Choroidal naevi are very common, being present in about one in ten individuals. They differ from malignant melanomas in that they usually:

• have a thickness less than 2 mm;
• do not cause symptoms;
• do not leak significant amounts of fluid;
• do not have large amounts of 'orange pigment' on their surface.

Iris naevi tend to be smaller than malignant melanomas, and usually not more than 3 mm in diameter.

In some patients, the only way to be sure that a tumour is a benign naevus and not a malignant melanoma is to observe the lesion for many years to ensure that the tumour does not grow.

Neurilemmoma
A very rare benign tumour arising from nerve tissue.

Osteoma
A very rare tumour consisting of bone within the eye, usually next to the optic nerve.

Retinoblastoma
This is a highly malignant tumour developing in the retina of a baby or infant. It develops when both the chromosome 13 inherited from the father and the chromosome 13 inherited from the mother are mutated (i.e., two-hit hypothesis). In some babies, both mutations occur in the same cell, so that only one retinoblastoma develops. Other babies inherit one mutation from a parent, so that every cell in the body is abnormal and so that they tend to develop numerous retinoblastomas in both eyes as well as other cancers in various parts of the body.

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