Among the many eye conditions that can affect dogs is one that isn't painful, but is nonetheless heartbreaking. Progressive Retinal Atrophy, or PRA, is a genetically inherited condition in which the eyes are basically "programmed" to go blind.

PRA can appear in any breed of dog, and is equally prevalent in purebred and mixed-breed animals. It's usually transmitted through a recessive gene, meaning two carriers of the gene must mate in order to produce an affected pup. The exceptions to this rule occur in Bull Mastiffs and Old English Mastiffs, where the PRA gene is dominant, so only one parent need have the gene in order to produce pups with PRA. Also, the gene is linked to gender in the Samoyed and Siberian Husky breeds. In these breeds, the disorder appears more often in males than females.

Atrophy occurs when tissues deteriorate, due to aging, disease or genetic abnormalities. The retina is the back portion of the eye that contains the "rods" and "cones" that process light signals coming in from the cornea. Or, in layman's terms, the retina provides the "film" in the camera that is the entire eye. In PRA, the retina gradually atrophies, causing the dog to go blind.

Dogs with PRA will first begin having difficulty seeing at night and in lower-level light. Over time the pupils become permanently dilated, and owners often report increased eye shine, or a "glow" coming from the eyes. How long the process takes varies from dog to dog, but blindness is the inevitable result. Most dogs are completely blind within six months to a year after being diagnosed by a veterinarian. However, antioxidant supplements tailored toward eye health have been somewhat successful in slowing down the deterioration of the retina. Pet owners who suspect their dog may have PRA need to have their dog examined by a veterinarian, preferably a board certified veterinary ophthalmologist.

The good news is that PRA develops slowly and is not painful, so most dogs with the condition are happy and adjust well to their decreasing vision. Some dogs develop cataracts once PRA is in full development. These cataracts are usually left in place, since surgery to remove them would not improve the dog's vision. Over all, the disease tends to be more distressing for the owners than for the affected animals.

For many (but not all) breeds there are genetic tests that can determine which animals are carriers of PRA. Dogs that are carriers (as well as dogs with the condition) obviously should not be bred. Further, if your pet has been diagnosed with this disorder, it's recommended you contact the breeder so he or she can be made aware of the problem as well.

It's important to remember that dogs with PRA can and do live happy, healthy and nearly-normal lives. As the owner, you can make a visually impaired pet's life easier by keeping its surroundings as consistent as possible and introducing any changes to the environment gradually. It's also best to establish a regular route for walks or any other exercise.