Scratchings-and-Sniffings

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Progressive Retinal Atrophy Posted: 24 Nov 2009 09:03 AM PST We've discussed glaucoma and cataracts and even lens luxation as potential causes of blindness in dogs. There are other conditions in the back of the eye that can lead to blindness, too. Progressive retinal atrophy is one such disease and, as the name suggests, it affects the retina. Light enters the eye and is reflected back to the retina through the lens. Sensitive cells, called rods and cones or photoreceptor cells, located in the retina turn this reflected light into visual images via electrical impulses from the optic nerve to the vision center in the brain. Retinal degeneration, or atrophy, obviously impairs this process.    The most common form of retinal disease is inherited and affects many purebred dogs and can affect mixed breed dogs, too. The age of onset is typically middle age for most dogs although there is a form of inherited retinal dysplasia, or poor development of the retina, that affects younger dogs and can result in early blindness. It can be difficult for most people to recognize that their dog is affected by PRA. Loss of vision at night or in low light is the first sign and dogs are pretty good at disguising their failing vision. A good sense of smell and familiarity with the home environment work in your dog's favor. The rods in the retina are the first cells to be affected by PRA and since these cells detect light, night vision is the first to go.   Another tell tale sign is reflectivity from the eye. In the right light conditions an owner may detect light being reflected through a dilated pupil from the back of the eye.   Veterinarians can detect PRA via an eye exam in some cases. A sophisticated diagnostic test called electroretinography is used by veterinary ophthamologists for a definitive diagnosis.   Abyssinian and Siamese cats can develop retinal atrophy, too, and any cat that gets a taurine deficient diet may develop the disease. Taurine is an amino acid that cats require in their diet. It's one of the big differences between cats and dogs and a reason cats need animal tissue protein in their diets.   There is no cure for PRA and it invariably progresses to complete blindness. Certain antioxidants may retard the progression but blindness will eventually occur. The only real hope for eliminating this disease is through annual testing and selective breeding. There is a genetic test available for the more common form of PRA for certain breeds and this test is highly recommended prior to breeding. Parents and siblings of dogs affected with PRA should not be bred as they may be carriers of the trait.    The good news for owners of dogs with PRA is that blindness is not the end of the world for a dog. As I noted before, the acute sense of smell and hearing in dogs gives them certain advantages. If you keep things consistent at home, like feeding and water bowls in the same place and if you don't move the furniture around a lot you will be surprised at how well your blind dog adapts. Needless to say you have to be careful when you take them outside but they still love their walks on the leash.   One of my neighbors has a blind dog that he walks almost daily. I've met this dog and when I yell out to him by name he wags the old tail just like a sighted dog.   That's the great thing about dogs. Self-pity is not in their repertoire of emotions.

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