Progressive Retinal Degeneration in Cats
Dr. Noelle McNabb
Progressive retinal degeneration or atrophy (PRD, PRA) is premature degeneration (deterioration) of the photoreceptor cells of the retina. There are two types of photoreceptors in the retina and these are the light-sensitive rods and cones. They are responsible for detecting light and converting it into an electrical signal that travels to the brain. When the photoreceptor cells deteriorate, vision is lost because the animal has no way to generate an image from the light reaching the retina. Dilated pupils
PRA/PRD is in cats initially affects the rods. The rods are responsible for dim light vision; therefore, the cat loses its nighttime vision first. The disorder is progressive and eventually the cones are affected. Over time, the cat slowly goes completely blind. The disease affects both eyes at the same time.
Most cats are seen in the late stages of disease and have advanced changes in their retinas because they compensate very well as their vision slowly deteriorates. Sometimes the blindness can appear to be sudden in onset (even though it has been developing for months) because the cat may show almost no signs until the last bit of vision has been lost.
PRA in cats is rare in the United States. It is seen most often in purebred cats, such as the Abyssinian, Persian, and Siamese. It is seen sporadically in domestic shorthair and other mixed breed cats. In the Abyssinian, the disease is inherited as a dominant trait, but the inheritance pattern is unknown for other cats.
What to Watch For
Bumping into objects, reluctance to jump up onto objects, reluctance to go outside, or other signs of blindness
Poor vision in dim light or darkness
More readily visible eye shine from the back of the eye due to dilation of the pupils
Diagnostic tests are needed to recognize PRA/PRD and exclude other diseases. Your veterinarian will probably take a complete medical history and perform a thorough physical examination.
A complete ophthalmic examination is indicated and involves all of the following tests. Your veterinarian may refer your cat to a veterinary ophthalmologist for completion of some of these tests:
Tests to evaluate vision, such as observing the cat as he navigates an obstacle course in both bright and dim light, and certain neurologic reflex testing
Pupillary light reflex testing
A Schirmer tear test and fluorescein staining of the cornea
Tonometry to measure the pressure within the eye
Specialized examination of the front chamber of the eye, the iris and lens, the vitreous and the retina.
If your veterinarian is concerned that some disease other than PRA is the source of the cat's blindness, then medical tests to rule out other causes may include the following:
A complete blood count (CBC) and serum blood tests
A feline leukemia virus (FeLV) test, a feline immunodeficiency virus (FIV) test and a toxoplasmosis titer to look for the presence of these infectious diseases
Plasma or blood taurine levels
A measurement of systemic arterial blood pressure to rule out high blood pressure
Possibly chest and abdominal X-rays
PRA can sometimes be confirmed at the time of retinal examination because it causes characteristic changes in the appearance of the retina. Early stages of the disease can be more difficult to diagnose, and in that instance the disease can be detected with the following test:
An electroretinogram to evaluate the function of the photoreceptor cells when they are stimulated with flashes of light. If the electroretinogram is abnormal, then the retina is diseased. If the electroretinogram is normal, then the origin of blindness is somewhere other than the retina.
No therapy is available to prevent, slow the progression of, or reverse the degenerative changes of PRA.
Early diagnosis of PRA using electroretinography is most important in catteries to eliminate individuals from the breeding pool that are either clinically affected or represent genetic carriers of the disease.
Care consists of providing a consistent and safe environment for pets with vision loss. Considerations include:
Establish a known location for the food and water bowls and guide your pet to them until he can memorize the locations.
Place barriers across staircases, over hot tubs and around pools.
Restrict activity on balconies; your cat could fall through the space between the guardrails.
Avoid changing the location of the furniture and leaving chairs or other objects out of place in the house. Your cat will memorize a familiar (stable) environment in a relatively short time.
Purchase toys that contain bells or other noisemakers to encourage and help cats to play.
Affected cats lose their vision in dim lighting first. Therefore, night-lights or plug-in hall lights are helpful for negotiating in the house at night.
It is important to realize that vision is the least important of the cat's three major senses. The sense of smell and the sense of hearing are more highly developed in cats than in people, and they rely heavily on these two senses. Cats that are blind are not as handicapped in the their activities as you would expect. At times they can act very normal. Because PRA develops so slowly, most cats adapt very well to their vision loss and remain happy and active pets.
No preventive care is available for an individual because PRA is genetic. Do not breed affected animals.