Progressive retinal atrophy (PRA), also known as progressive rod and cone degeneration (PRCD), refers to a group of degenerative eye disorders that eventually lead to permanent blindness in both eyes. The retina is a delicate, thin membrane lining the back of the eyes. It is responsible for absorbing and reflecting light. When the retina is damaged or diseased, it loses its ability to perceive light. PRA targets the retinal photoreceptors, which are crucial to vision.
Causes of Progressive Retinal Atrophy in Dogs
The cause of PRA is not completely understood. It has been identified as an inherited, autosomal recessive genetic disorder that affects more than 80 domestic canine breeds. It was first discovered in the Gordon Setter.
Prevention of Progressive Retinal Atrophy
Any dog intended to be used for breeding should be examined by a board-certified veterinary ophthamalogist and screened for the presence of inherited eye diseases. Most veterinary eye specialists are affiliated with the Canine Eye Registry Foundation, or CERF. Only dogs free from progressive retinal atrophy and at a low risk of being a carrier of the PRA gene should be bred. Carriers are those dogs that do not themselves have PRA, but do have affected dogs in their ancestry. There are several commercially available genetic tests that can identify dogs that are normal, carriers of or affected by PRA at an early age.
Retinal degeneration, without more, is not painful. Most dogs adjust unusually well to progressive loss of vision.
The signs of progressive retinal atrophy (PRA) can appear early or later in life and can be slow or sudden in onset. The dog's familiarity with its environment often delays diagnosis, because its vision impairment can be quite difficult to detect.
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
Dogs At Increased Risk
Early-onset, slowly progressive PRA causes night blindness during the first year of life, although affected dogs may retain daytime vision for a year or more. Affected breeds include the Akita, Tibetan Terrier, Dachshund, Gordon Setter, Miniature Schnauzer and Norwegian Elkhound, among others.
Early-onset, rapidly progressive PRA causes vision impairment that starts in the first year of life and progresses to blindness within a matter of months. Breeds affected by this form of PRA include the Irish Setter, Cardigan Welsh Corgi and Collie, among others.
PRA can also occur after 2 years of age, with complete blindness usually occurring by age 4. Dogs affected by this form of the disorder include the Border Collie, Afghan Hound, Miniature and Toy Poodle, Cocker Spaniel, Tibetan Terrier, Akita, Samoyed, Siberian Husky and Labrador Retriever, among others.
Healthy, middle-aged and older female dogs between 6 and 14 years of age tend to develop a sudden and severe form of progressive retinal atrophy, where vision is completely lost in both eyes over the course of several hours to several days. Males are less commonly affected by this form of the disease.
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.
How Progressive Retinal Atrophy is Diagnosed
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.
Unfortunately, PRA is irreversible and untreatable. Fortunately, however, most affected dogs adjust quite well to blindness, as long as their living environment is not rearranged very frequently.
Treatment and 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.