Progressive retinal atrophy (PRA) is a group of genetic diseases seen in certain breeds of dogs and, more rarely, cats. Similar to retinitis pigmentosa in humans, it is characterized by the bilateral degeneration of the retina, causing progressive vision loss culminating in blindness. The condition in nearly all breeds is inherited as an autosomal recessive trait, with the exception of the Siberian Husky (inherited as an X chromosome linked trait) and the Bullmastiff (inherited as an autosomal dominant trait). There is no treatment. Types of PRA
In general, PRAs are characterised by initial loss of rod photoreceptor cell function followed by that of the cones and for this reason night blindness is the first significant clinical sign for most dogs affected with PRA. As other retinal disorders, PRA can be divided into either dysplastic disease, where the cells develop abnormally, and degenerative, where the cells develop normally but then degenerate during the dogs lifetime.Generalized PRA is the most common type and causes atrophy of all the neural retinal structures. Central progressive retinal atrophy (CPRA) is a different disease from PRA involving the retinal pigment epithelium (RPE), and is also known as retinal pigment epithelial dystrophy (RPED). Generalized PRA
Commonly affected breeds:
Akita - Symptoms at one to three years old and blindness at three to five years old. Selective  breeding has greatly reduced the incidence of this disease in this breed. Miniature longhaired Dachshund - Symptoms at six months old. Papillon - Slowly progressive with blindness at seven to eight years old.
Vision is better in low light and better for moving or distant objects. Not all affected dogs go blind. Secondary cataracts are common. Commonly affected breeds
Labrador Retriever
Golden Retriever
Border Collie
Collie
Shetland Sheepdog
English Cocker Spaniel
English Springer Spaniel
Chesapeake Bay Retriever
Cavalier King Charles Spaniel
Briard - has an especially high frequency.It can also be found in the poodle varieties

Hereditary retinal dysplasia
There is another retinal disease in Briards known as hereditary retinal dysplasia. These dogs are night blind from birth, and day vision varies. Puppies affected often have nystagmus. It is also known as lipid retinopathy. Diagnosis
Progressive vision loss in any dog in the absence of canine glaucoma or cataracts can be an indication of PRA. It usually starts with decreased vision at night, or nyctalopia. Other symptoms include dilated pupils and decreased pupillary light reflex. Fundoscopy to examine the retina will show shrinking of the blood vessels, decreased pigmentation of the nontapetal fundus, increased reflection from the tapetum due to thinning of the retina, and later in the disease a darkened, atrophied optic disc. Secondary cataract formation in the posterior portion of the lens can occur late in the disease. In these cases diagnosis of PRA may require electroretinography (ERG). For many breeds there are specific genetic tests of blood or buccal mucosa for PRA.Absent a genetic test, animals of breeds susceptible to PRA can be cleared of the disease only by the passage of time—that is, by living past the age at which PRA symptoms are typically apparent in their breed.