out of sight: a look at progressive retinal atrophy
Progressive retinal atrophy (PRA) is a group of inherited diseases of the retina that eventually cause blindness. While common in dogs, it is quite rare in cats.
The retina lines the back of the eye and converts the light that enters the eye into electrical nerve signals that travel through the optic nerve up to the brain. Progressive retinal atrophy causes the receptors on the retina to die prematurely, leading to complete blindness over time.
The onset of PRA depends partly on how the photoreceptors on the retina are affected. Some forms of PRA happen because photoreceptors never formed properly in the first place, and some forms of PRA happen when photoreceptors form properly but then degenerate (which is what happens most commonly).
Vision loss can start as early as 12 weeks old in the early onset form of PRA, causing complete blindness by one or two years of age. Some degenerative forms start in early adulthood, and some as late as 9 to 11 years of age.
We see PRA most commonly in purebred dogs, though mixed breed dogs can be affected, too.
Breeds that are prone to have malformed photoreceptors include:
- Norwegian Elkhound
- Irish Setter
- Cardigan Welsh Corgi
- Miniature Schnauzer
Breeds that are prone to the more common degenerative form of PRA include:
- Miniature poodles
- Cocker Spaniels
- Tibetan Terriers
- Longhair and Wirehair Dachshunds
- Labrador Retrievers
PRA starts slowly and advances over time. This has advantages, as it allows your pet to cope with her changing vision slowly. The disadvantage, however, is that many times, owners have no idea that it is happening! You may notice subtle changes at first, especially at night. Your pet may be reluctant to go outside at night, or may hesitate on a dark stairwell. Eventually, both eyes will become blind, and this is when most owners take notice.
Your veterinarian may have the tools needed to diagnose PRA, or you may be referred to a veterinary ophthalmologist, who will examine the back of your pet’s eye with special lenses. Electroretinography may be performed to examine the electric responses in the retina to confirm PRA.
Currently, there is no treatment or cure for PRA. The disease is painless, though, and pets do quite well with blindness. Remember that their sense of smell and hearing are much more important to them, and generally their blindness seems to affect us more than it does them! If you’ve gotten a diagnosis of PRA, talk to your veterinarian about ways to make your blind pet more comfortable in and out of the home.