Definition of PRA in Dogs
Progressive retinal atrophy (PRA), also known as progressive rod and cone degeneration (PRCD), refers to a group of degenerative eye disorders that cause blindness in both eyes. The retina is a delicate membrane lining the back of the eyes. It is responsible for absorbing, reflecting and perceiving light and is essential to vision. PRA isn’t well-understood, although it probably is a genetic disorder. The first symptom of PRA is night blindness. Affected dogs are reluctant to go down stairs, go outside, navigate unfamiliar areas or jump on or off furniture in darkness or dim light. The surface of their eyes becomes cloudy, gray, and may take on a greenish sheen. As the disease progresses, dogs bump into furniture and walls and stumble over familiar objects. Fortunately, retinal atrophy rarely is painful, and most dogs adjust to the progressive loss of vision. Owners should consult with their veterinarian to accurately diagnose and manage this condition.
Symptoms of Progressive Retinal Atrophy in Dogs
Usually, the first sign of progressive retinal atrophy is night blindness, including a reluctance to go outside at night or to navigate unfamiliar areas in dimness or darkness. Other signs can include:
- Reluctance to jump on or off furniture during darkness
- Night blindness (nyctalopia); reduced vision in dim light
- Sluggish pupilary light responses
- Decreased menace response
- Cloudy or opaque eye surface; grayish discoloration of the surface of the eye
- Greenish sheen to the eye
- Bumping into furniture or walls
- Tripping or stumbling over objects
- Pawing at the air when going down stairs
- Reluctance to navigate stairs
Preventing PRA in Dogs
Most forms of progressive retinal atrophy are passed from parent to offspring in an inheritance pattern known as “autosomal recessive.” This is especially true in Collies, Irish setters, Miniature poodles, Cocker spaniels, Briards, and Labrador retrievers. In these breeds, if a dog has inherited the gene responsible for PRA from only one parent, it will not develop the disease but will be a carrier of the trait – meaning that if bred, it can pass that gene on to its offspring. However, if a dog inherits the “PRA gene” from both parents, it will eventually develop clinical PRA.
In several breeds, particularly Samoyeds and Siberian huskies, PRA is passed on in a dominant inheritance pattern, meaning that even if a dog gets only one copy of the gene, it will develop the disease. In many breeds, the mode of inheritance is not known.
The key to preventing PRA is held by responsible breeders of affected breeds. These animals should be genetically screened for PRA by a board-certified veterinary ophthalmologist and have the results of that screening registered through the Canine Eye Registration Foundation (CERF). Dogs found to be carrying the gene for PRA – whether or not they actually have the disorder – should not be bred. Offspring of affected dogs likewise should not be bred. Responsible breeding practices are the only way to remove animals with PRA from the breeding population.
Genetic testing of blood samples is available to identify whether a particular dog carries the gene for PRA. The best way to ensure that your new dog does not carry the PRA gene, and therefore will not develop the disorder, is to have both of its parents tested, if possible. This is especially important if the dog you are considering belongs to one of the commonly affected breeds, and even more so if you are thinking about breeding the animal in the future. Any dog found to be carrying a PRA gene should be spayed or neutered.
How Progressive Retinal Atrophy is Diagnosed
PRA is diagnosed through extensive eye examinations. In many cases, general practice veterinarians will refer the owner to a specialized veterinary ophthalmologist to perform the diagnostic tests and arrive at a diagnosis. Routine eye examination can suggest the presence of progressive retinal atrophy. A definitive diagnosis typically is made by a veterinary eye specialist using an electroretinogram (ERG) to measure the retina’s ability to respond to light. During this examination, one electrode is placed on the dog’s cornea, and neutral electrodes are placed on the skin around the eye. The results of this test are conclusive.
Treatment & Prognosis
Progressive retinal atrophy (PRA) is always bilateral (affects both eyes) and always ends in complete blindness. There is no way to reverse or to treat retinal degeneration, or the total loss of vision that inevitably accompanies it.
Progressive retinal atrophy will eventually result in blindness. There is no cure, prevention, or treatment currently available. However, with minor environmental accommodation (avoid rearranging the furniture, etc.), most affected dogs adjust very well to vision loss and can live long and healthy lives, particularly if their sight deteriorates gradually.