Samoyed - More severe disease than the Husky. Dominant PRA
Bullmastiff - Inherited as an autosomal dominant trait due to a mutation in the gene for rhodopsin. Feline PRA
Abyssinian - Two forms exist. One is inherited as an autosomal dominant trait and has an early age onset. The other is inherited as an autosomal recessive trait and has a middle age onset. Early onset PRA has also been reported in the domestic shorthaired cat and Persian. The Siamese also likely has a hereditary form of PRA. Despite belief among breeders to the contrary, there is apparently no link between coat color in Persians and the development of PRA. Central progressive retinal atrophy (CPRA)
CPRA is also known as retinal pigment epithelial dystrophy (RPED). The cause of this condition is the loss of the retinal pigment epitheliums ability to effectively process the photoreceptor outer segment (POS) and subsequent accumulation of POS material in the RPE and loss of function. The loss of function of the RPE leads to photoreceptor degeneration. Vitamin E deficiency may play a role in the development of CPRA. It is characterized by accumulation of pigment spots in the retina surrounded by retinal atrophy and a mottled appearance of the pigmented nontapetal fundus. The pigmented spots eventually coalesce and fade as the atrophy of the retina increases. It is an inherited condition (in the Labrador Retriever it is inherited as an autosomal dominant trait with variable penetrance). CPRA occurs in older dogs. Peripheral vision is retained for a long time.
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.