The Uvea

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Uveal inflammation is associated with several systemic diseases as well as being caused by local infection

The uvea is the site of several inflammatory processes, collectively known as uveitis.
Depending on the preferential site of inflammation, these may be manifest as choroiditis, iritis, cyclitis (inflammation of ciliary body), iridocyclitis or, when all sites are involved, generalized uveitis.

Uveitis is one of the causes of an acutely painful, red, inflamed eye. Histologically, there is lymphocytic and sometimes granulomatous inflammation of the uvea. In iritis this causes exudates in the aqueous, which are visible as keratic precipitates. In choroiditis, inflammatory exudation can cause detachment of the retina, whereas inflammatory destruction of the pigment epithelial layer causes degeneration of overlying photoreceptors, which normally depend on this layer for support.
Uveitis can be caused by several disease processes, the most common being immune-mediated and associated with other systemic diseases such as sarcoidosis, rheumatoid disease, ankylosing spondylitis, Reiter's syndrome, and inflammatory bowel disease. Infection with cytomegalovirus or Toxoplasma, often as a complication of immunosuppression, can cause severe choroiditis leading to blindness. The larva of Toxocara canis can reach the eye to cause severe inflammation in the choroid, spreading to the retina (chorioretinitis) and vitreous, at which stage blindness results.

Melanocytic tumours commonly arise in the uvea and may be benign or malignant

The melanocytes of the uvea are the cells of origin for benign melanocytic naevi as well as ocular malignant melanomas. 

Most benign melanocytic naevi arise in the iris and are seen as abnormal areas of pigmentation. They often change in appearance with time, bringing them to medical attention. Most lesions are proliferations of spindle-shaped melanocytes.

Ocular malignant melanomas can arise anywhere in the uvea (5% arise in the iris, 10% in the ciliary body, and 85% in the choroid). Depending on the site of origin, tumours cause different types of symptom leading to impaired vision. Macroscopically, tumours are darkly pigmented lesions, typically 1،2 cm in diameter, which cause detachment of overlying retina.

There are two main histological patterns of ocular melanoma:

1 Spindle-cell melanomas tend to have little pleomorphism and few mitoses, and are usually localized to the globe. If they are excised completely, 10-year survival is around 90%.

2 Epithelioid melanomas show large cells with pleomorphism and many mitoses. This type is associated with a 10-year survival of 35%, orbital invasion frequently being encountered at time of diagnosis.

Spread of ocular melanomas occurs directly into the orbit, or haematogenously to cause systemic metastasis. Late manifestation of metastatic disease from excised orbital melanomas is a well-recognized phenomenon.
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