The retina is a thin, delicate membrane that lines the back of
the eye and is actually an extension of the optic nerve. In a healthy cat, the
retina receives light, processes it, and passes it on to the brain. If the
cells are damaged, it can’t send anything on. In a cat with retinal disease,
the retinal cells are damaged and the eye is no longer able to properly
transmit information regarding the light it receives. The visual image may be
blurred, and part or all of the visual field may be blacked out.
Retinal diseases usually begin with the loss of night vision.
When this happens, the cat hesitates to go out at night or won’t jump onto or
off furniture in a darkened room.
Progressive Retinal Atrophy
Progressive retinal atrophy is the degeneration of the retinal
cells over time. In cats, retinal diseases usually are not caused by genetic
influences, although a hereditary form of progressive retinal atrophy occurs in
Persians, Abyssinians, and possibly Siamese. The mode of inheritance appears to
be autosomal recessive.
Treatment: Progressive retinal atrophy has no treatment and
eventually leads to blindness. It is hoped that a genetic screening test will
be available in the future so breeders can avoid this problem.
Retinitis is a disease in which inflammation of the retina
leads to degeneration and destruction of the light receptors. It occurs in
association with toxoplasmosis, feline
infectious peritonitis, lymphoma, cryptococcosis, and systemic fungus infections. It may
also occur as a consequence of hypertension, or eye injury, or for unknown reasons. In
these cases, the retina may actually become detached from the back of the eye.
High blood pressure or hypertension is one of the most common causes of
this condition. The hypertension is usually associated with hyperthyroidism and/or renal
failure. Immediate medical treatment may stop the progression of this
Treatment: The outlook for useful vision depends on the cause
and extent of retinal damage at the time of diagnosis. Medical diseases, such
as hypertension, are treatable. Control or cure can prevent further damage. If
caught early, retinal detachments caused by trauma may sometimes be repaired -
or at least, further damage can be prevented. This requires referral to a
Central Retinal Degeneration
A dietary deficiency of the essential amino acid taurine
produces a type of retinal degeneration in cats that initially involves the
central portion of the retina. Because this is the area where the cat sees
best, he is unable to see stationary objects well. The cat retains some
peripheral vision and thus is able to detect moving objects seen at the
periphery. This dietary cause is rarely seen now, since cat food manufacturers
have added supplemental taurine to most cat foods.
The antibiotic enrofloxacin is also associated with a type of
retinal degeneration. Some cases improve if the medication is stopped right
away, but not all.
Treatment: Taurine deficiency is slowly progressive, but
correcting the diet stops the process.