Progressive retinal atrophy

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 dog's 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. • Tibetan Spaniel - Symptoms at three to five years old. • Tibetan Terrier - PRA3/RCD4 disease of middle age dogs. http://www.ttca-online.org/html/Petersen-Jones_PRA_article.pdf • Samoyed - Symptoms by three to five years old. Rod-cone dysplasia This type of PRA has an early onset of severe vision loss. It is caused by a defect in the gene for cGMP-phosphodiesterase, which leads to retinal levels of cyclic guanosine monophosphate ten times normal. Rod-cone dysplasia type 1 • Irish Setter - Rod cell response is nearly absent. Night blindness by six to eight weeks old, often blind by one year old. 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 epithelium's 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. 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. 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. Breeds in which the PRA gene is recessive may still be carriers of the gene and pass it on to their offspring, however, even if they lack symptoms, and it is also possible for onset of the disease to be later than expected, making this an imperfect test at best. ==Management==

There is no treatment for PRA. However, most dogs that suffer from this disease adjust remarkably well. To maximize the quality of the dog's life, follow these guidelines: • Do not rearrange furniture, as the dog has memorized the layout of the environment • Use a short leash when walking a dog with blindness from advanced PRA • Erect safety barriers around pools or balconies ==See also==