Overview PRA (Progressive Retinal Atrophy) is common in MANY breeds of dogs (including mixed breeds).
PRA affects the entire retina and is the canine equivalent of retinitis pigmentosa. This disease manifests itself differently in different breeds. The most common form of PRA in the collie is detectable at early age (6wks and over). The form of PRA in Irish Setters is also early-onset. In Labrador Retrievers, on the other hand, the age of onset is much later, typically four to six years of age, making it much harder to find and isolate carriers in this breed. PRA has been detected as early as six weeks in puppies, and these puppies are usually blind by six to eight months. An electroretinography can be used to detect the early signs of PRA. Animals to be tested in this manner are anesthetised while lenses are placed on the eyes to record the retina's reaction to light. (Like wearing contacts.) In other cases, ophthalmological examination by ACVO-certified vets can pick up cases of PRA and confirm them with electroretinography if desired.
All dogs affected with PRA eventually go blind. Carriers show no clinical symptoms. Symptoms are subtle, starting with night blindness, some eye dilation, to progressive blindness. It's quite common to not notice anything is wrong until the dog is nearly completely blind. Proactive testing is always recommended, especially for breeding stock. Current research is beginning to isolate the genetic markers for this disease. At present, there is a genetic test to identify carrier and affected dogs in the Irish Setter breed. Work is underway for one for the Labrador Retriever. This disease is thought to be a simple autosomal recessive gene. Thus two recessive genes are needed for a dog to be affected. A single recessive gene masked by the healthy dominant means the dog is a carrier. Therefore, an affected dog's parents are carriers or also affected.