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Ocular Melanocytosis

Issue Description
A disease of the eye which in dogs is almost found exclusively in the Cairn Terrier. Until recently it was known as pigmentary glaucoma. The disease is caused by an increase of melanocytes in the iris, sclera, and surrounding structures. This infiltration of pigment can block the part of the eye through which fluid drains. The increased fluid in the eye leads to increased pressure, which is glaucoma.
Other Names
Ocular Melanosis, OM, Melanosis Oculi

OM occurs when there is a proliferation of pigment in the eye fluid that causes a blockage of drainage pathways just outside the rim of the cornea. The age of onset for this disorder is often between five and eleven years of age, but OM has been seen in younger Cairn Terriers. As an affected dog ages, the build-up of pigment creates plaques (of pigment) that block the drainage of eye fluid. When the drainage gets blocked, the fluid pressure inside the eye increases, and the dog develops a secondary glaucoma. This elevated pressure causes the dog pain and, eventually, blindness from all the damage caused by the fluid pressure.

It is very important to identify the disease early. If OM and especially glaucoma are identified in time, a Cairn Terrier can receive a number of medications that will (1) reduce the amount of fluid that the eye produces, (2) increase the removal of fluid from the eye, and (3) reduce the production of pigment in the eye. These drugs all act to reduce the pressure in the eye. Unfortunately, the medication often eventually fails to control the pressure. When that happens, the dog will again experience pain and removing the eye may be the only remaining option. This disorder usually affects both eyes.

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