EYE TUMORS
Seventy-five percent of cat eye tumors are malignant and aggressive forms of cancer (in dogs, the ratio is reversed, with 75 percent of tumors being benign and not spreading or life-threatening) . An iris melanoma is the most common type of tumor that affects the eyes of cats. Older cats may develop a visible brown or black spot on the iris of the eye. The Iris is the colored part of the eye. The spots can be single or multiple and are pigmented cells called melanocytes that have overgrown. The examination involves the use of a slit-lamp biomicroscope, which determines whether or not the tumor is cancerous. If the pigmented area of the iris is flat, the lesion is called Ins Melanosis. This is considered precancerous and is rechecked at six-month intervals.
MELANOMA OF THE IRIS / GLAUCOMA
Iris melanoma is also called Melanosis and/or Melanocytoma. Iris melanoma is the term used if the pigmented area of the iris is raised. This is a cancerous lesion. The treatment involves the use of a diode laser to destroy cancer cells. Without treatment, melanoma of the iris usually results in glaucoma. Glaucoma occurs because cancer cells spread and block the drainage angle of the eye, which is where fluid normally drains into the eye. Since fluid cannot drain from the eye, it builds up inside the eye, increasing the pressure inside the eye and causing glaucoma. In dogs, glaucoma rapidly leads to blindness due to irreversible damage to the retina.
The only sign of glaucoma in cats may be a slight difference in the size of the pupils, which are the central dark area of the eye. Surgical removal of the eye, which is called enucleation, is often necessary in advanced cases of Ins Melanoma. This relieves Glaucoma pain and removes the cancerous mass.
RETINAL DEGENERATION
Retinal degeneration is an inherited condition in Abyssinian cats. It occurs between four and six years of age and results in blindness. A dietary deficiency of the amino acid taurine can also occur in cats fed primarily dog food, resulting in nutritional degeneration of the retina. This condition was first described in 1975 and was named Feline Central Retinal Degeneration (FCRD). Commercial cat foods are now fortified with taurine to prevent this problem.