Progressive Retinal Atrophy (PRA)
Progressive Retinal Atrophy (PRA) is an inherited disease of the retina (the "film in the camera") in dogs, in which the eyes are genetically programmed to go blind. PRA occurs in both eyes simultaneously and is nonpainful. There are many different types of inherited retinal degenerative diseases in purebred dogs, and discussing these are beyond the scope of this article. PRA occurs in most breeds of dogs and can occur in mixed breeds also. It is recessively inherited in all breeds studied, with the following exceptions: PRA is dominantly inherited in Old English Mastiffs and Bullmastiffs, and PRA is sex-linked and found primarily in male dogs in the Siberian Husky and Samoyed breeds.
The first clinical sign that the owner often notices is that the pupils are dilated; owners often notice a "glow" and increased "eye shine" from the eyes. By the time this is noticed, the dog is usually at least night blind (not able to see well in low light surroundings). Clinical signs in dogs with PRA vary from the dog first becoming night blind in the early stage of PRA, to the entire visual field in all light levels becoming affected in advanced PRA. In the final stage of PRA, the dog is completely blind. It has been very commonly stated in the veterinary medical literature that all dogs with PRA will eventually develop blindness from advanced PRA. The literature also commonly states that the time frame until the dog is blind varies considerably from dog to dog. Usually, however, complete blindness occurs within one year of diagnosis (with diagnosis confirmed by a veterinary ophthalmologist) if antioxidant supplementation is not being given.
Dogs with PRA usually develop cataracts that are termed "toxic cataracts", in the mid to late stages of PRA. Cataracts are opacities within the lens, and usually both eyes of dogs with PRA develop cataracts. There are many causes of toxic cataracts, but the most common cause in dogs is PRA. As the retinal tissue slowly dies, it releases toxic by-products of cell death that are absorbed by the lens, causing lens damage and cataract development. The cataracts can be severe enough to aggravate vision loss. In addition to supporting retinal health in dogs with PRA, antioxidant nutritional supplementation may help reduce the severity and slow the progression of toxic cataracts. If retinal function is completely lost in a dog with PRA but toxic cataracts are mild, antioxidant supplementation with Ocu-GLO Rx™ might be continued in these patients to help support lens health in an attempt to delay cataract progression. This is because while vision cannot be restored, there can be painful complications from the development of advanced cataracts. Cataract surgery would not be performed in these patients, as it would not help restore any functional vision.
If the toxic cataracts interfere with vision but reasonable retinal function is still present, cataract surgery – under very limited circumstances – might be considered. A general rule of thumb is that cataract surgery is not performed in dogs with PRA. It is the belief of Dr. McCalla, however, that a dog with PRA that is on acceptable oral antioxidant supplementation and still has some viable retinal function might undergo cataract surgery under limited circumstances. Following surgery, it is unknown for each patient how long vision will be present until all retinal tissue dies – PRA is a genetic progressively blinding disease, and removing the cataractous lens does not "fix" the retina. It must be emphasized that the overwhelming majority of dogs with PRA are not suitable candidates for cataract surgery. It is also important to know that advanced cataracts can cause inflammation and subsequent pain and further damage to the eye; therefore, if cloudiness and/or pain develops in the eye(s) of dogs with PRA, ophthalmic re-examination by a veterinary ophthalmologist is recommended ASAP. Secondary painful complications that might occur include glaucoma and lens luxation.
It is important to understand that dogs with PRA are usually happy dogs with an acceptable quality of life. The retinal damage is not painful, and dogs usually adjust very well to their slow loss of vision. In fact, if a dog were destined to become blind and Dr. McCalla could pick the disease, it would be PRA; vision loss is slow and nonpainful, and the dog is given much time to adjust to progressive blindness. As mentioned earlier, however, PRA is not necessarily a hopeless disease as far as continued vision loss is concerned; affected dogs that still have some vision may benefit from specific antioxidant supplementation to support retinal and lens health.
It is also important to realize that it is OK to grieve about your pet's vision loss, but you must not put your sad feelings in your dog's head—they aren't really there! Your dog is not suffering. They adjust well to their vision loss, and it is by far hardest to deal with on the owner's side. Your dog's job description has not changed. Your blind dog is happy as long as its routine is stable. From your dog's point of view, life continues to be great-- you are there as always, and they just need to use their other keen senses a bit more to get the same information they used to view. Keep household furniture in its place, and consider purchasing the book "Living With Blind Dogs" by Caroline Levin. Animal Eye Care also sells this book. It is the only book of this subject matter, and is beneficial in helping owners and their affected pets adjust to the vision loss. Animal Eye Care also sells pet medical alert tags. One tag reads "I Have Poor Vision" while the other reads "I Am Blind". Please contact our office if you want to purchase a tag for your pet.
There are DNA blood tests available, to determine if dogs are likely affected with PRA, are likely carriers for PRA, or are not likely carrying the PRA gene. These tests are usually performed on purebred showdogs and breeding animals. Please visit this web site for further information: www.Optigen.com. If your dog is DNA-tested and found to be affected with PRA (but still has functional vision), it might benefit from oral antioxidant nutritional supplementation to support retinal and lens health. Additionally, if your purebred dog has been diagnosed with PRA by a veterinary ophthalmologist, the dog might be eligible for free DNA testing by Optigen as part of their ongoing research program. Any purebred dog that has been examined by a board-certified veterinary ophthalmologist (ACVO, ECVO) and that has been definitively diagnosed with PRA is eligible for review for possible inclusion in the Free Testing Program. Visit www.Optigen.com for more information.