Progressive retinal atrophy in cats is a type of premature deterioration of the photoreceptor cells in the retina. There are two types of photoreceptor cells in the retina, cones and rods. These cells detect light and send the neural signals that allow the brain to interpret that light as images. Progressive retinal atrophy (PRA) in cats is a progressive disease that results in gradual loss of eyesight and eventual blindness.
How PRA Causes Vision Loss in Cats
In cats, progressive retinal atrophy usually affects the rods of the eye first. These cells are responsible for night vision. Cats with PRA lose their night vision first.
PRA is a progressive disease, and will eventually affect the cones of your cat's eye. These cells are responsible for day time vision. As your cat's cone cells deteriorate, he will go completely blind. Progressive retinal atrophy affects both of your cat's eyes at once.
Symptoms of PRA in Cats
The blindness associated with PRA may seem to appear suddenly, though in fact cats adjust very well to vision loss and may have been slowly losing their sight for some time before blindness becomes total and obvious to the owner. Many cats show no signs of illness until total vision loss occurs. Most cats diagnosed with PRA are already in the later stages of the disease.
Symptoms of PRA include blindness, bumping into things, reluctance to jump up or down or reluctance to go outside. Cats may exhibit poor vision in low light conditions; that's one of the first signs of PRA. Pupils will remain dilated as your cat loses vision, and your cat's eyes may seem to reflect more light once his pupils become more dilated.
Feline progressive retinal apathy is rare in the U.S. Purebred cats, such as the Siamese, Persian and Abyssinian succumb to this illness more often, though it may appear in mixed breed short hair cats. Progressive retinal atrophy in Abyssinian cats appears to have a strong link to heredity, though vets don't know what genetic factors may be involved in cases of PRA in other breeds.
Diagnosing and Treating PRA in Cats
Your vet will need a complete medical history and physical exam to diagnose PRA. Your vet will perform a number of tests designed to measure the extent of your cat's vision loss. A common test used to measure the extent of vision loss involves evaluating your cat's performance on an obstacle course under both dim and bright light conditions. Your vet will also test your cat's neural reflexes and your cat's pupillary response to light.
You may need to see a veterinary opthalmologist to determine the extent of the damage to your cat's eyes. The opthalmologist may take corneal stains and measure the pressure levels within your cat's eye, as well as examining the structures of your cat's eye.
PRA can't be cured, and there's no therapy to treat it. Cats can adjust quite happily to vision loss, though cats with PRA should not be bred, since the disease has a genetic component.