EYE TUMORS
Seventy-five percent of eye tumors
in the cat are malignant, aggressive forms of cancer (in dogs the ratio
is reversed, 75 percent of tumors are benign and do not spread or
become life-threatening). An Iris melanoma is the most common type of
tumor affecting cat's eyes. Older cats may develop a visible brown or
black spot on the iris of their eye. The Iris is the colored part of
the eye. The spots may be single or multiple and are pigmented cells
called Melanocytes that have overgrown. Examination involves the use of
a slit-lamp biomicroscope, which determines whether or not the tumor is
cancerous. If the pigmented area on the iris is flat, the lesion is
referred to as an Ins Melanosis. This is considered to be pre-cancerous
and is rechecked at six-month intervals.
IRIS MELANOMA / GLAUCOMA
Iris
melanoma is also called Melanosis and/or Melanocytoma. Iris melanoma is
the term used if the pigmented area on the iris is raised. This is a
cancerous lesion. Treatment involves using a diode laser to destroy the
cancer cells. Without treatment, Iris melanoma is generally result in
Glaucoma. Glaucoma occurs because the cancer cells spread and obstruct
the drainage angle of the eye, which is where the fluid within the eye
normally drains. Since fluid can not drain from the eye, it builds up
within the eye which increases pressure within the eye and causes
Glaucoma. In dogs, Glaucoma rapidly results in 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
dark central area of the eye. Surgical removal of the eye, which is
called Enucleation, is often necessary in advanced cases of Ins
Melanoma. This alleviates the pain of Glaucoma and removes the
cancerous mass.
RETINAL DEGENERATION
Retinal Degeneration
is an inherited condition in Abyssinian cats. It occurs between four to
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 which
results in Nutritional Retinal Degeneration. This condition was first
described in 1975 and was called Feline Central Retinal Degeneration
(FCRD). Commercial cat foods are now fortified with Taurine to prevent
this problem.
