Progressive retinal atrophy (PRA; also known as PRCD, progressive rod and cone degeneration) was first discovered in the Gordon Setter in 1911 and is now recognized in more than 86 breeds. PRA includes several specific inherited types of the diseases. In most instances the mode of inheritance is an autosomal recessive gene. In all cases there is destruction of retinal cells in both eyes, leading to blindness. There is no treatment for PRA.
The initial sign of PRA is night blindness. The dog hesitates to go out at night and won't jump on or off furniture in a dark room. As vision loss progresses, the dog develops other signs of impairment. For example, the dog may go up but not down a flight of stairs. Other behavioral changes also suggest loss of vision.
Early onset slow progression PRA causes night blindness during the first year of life but dogs may retain daylight vision for a year or longer. Breeds affected by this type of PRA include the Akita, Miniature Schnauzer, Norwegian Elkhound, Tibetan Terrier, Dachshund, and Gordon Setter.
Early onset rapid progression PRA causes visual impairment beginning during the first year of life and progressing to complete blindness in a matter of months. Breeds affected by this type include the Collie, Irish Setter, and Cardigan Welsh Corgi.
Late onset PRA causes night blindness that is noted after 2 years of age. Complete blindness occurs by age 4. This variant affects the Afghan Hound, Border Collie, Cocker Spaniel, and Labrador Retriever. Sudden acquired retinal degeneration is a disease of unknown cause found most often in healthy, middle-aged female dogs 6 to 14 years of age. It produces rapid and complete loss of vision in both eyes in a matter of hours to several days.
An electroretinogram (ERG), which measures the retina's response to light using a corneal electrode and neutral electrodes placed on the skin around the eye, may be done to definitively diagnose PRA after a CERF exam has suggested this diagnosis.
Prevention: It is important to certify all breeding stock and register all offspring with CERF or the GDC. Breed only those dogs who are free of PRA and are at low risk for carrying and transmitting the gene. Carrier dogs can be identified by pedigree analysis - if it is known which ancestors in the pedigree had PRA.
For example, knowing that a dog has PRA (an autosomal recessive trait) automatically tells you that both parents were at least PRA carriers and may even have been affected. Pedigree information may be available through open registries such as the GDC or through those sponsored by breed clubs; or in specific instances from conscientious breeders who keep meticulous records and are willing to share the information.
For many breeds there are now genetic tests that can identify affected, normal, and carrier dogs at an early age. VetGen and Optigen are two companies that offer this type of testing.
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