Progressive Retinal Atrophy (PRA) is an inherited, genetic disease that causes vision loss.
Breed Predisposition1. Australian Cattle Dogs
4. Cocker Spaniels
1. Night blindness: Dogs affected with PRA may initially show signs of night blindness. This is because PRA first affects the rod cells of the retina, which are used for night vision. At this stage the affected dog may just be reluctant to go outside, may seek out lights, or may actually bump into things during the night.
2. Green or yellow reflection from the eyes: Some dogs are noted to have increased green or yellow reflection from the eyes. This increased reflection develops as the retinal degeneration allows more reflection from the mirror like tapetum at the back of the eye.
3. Vision Loss: With time the day vision begins to degenerate as the PRA eventually affects the cones in the retina. These cells are responsible for vision during the day. The development of the vision loss can be quite variable. Some dogs loose their vision 6 months after developing night blindness, other dogs may take 36 months or longer to loose vision.
Some dogs cope so well with the slow progressive vision loss in their own environments that they know, that are only noted to be blind when the environment is changed, or when cataracts have been noted to be present. In dogs with mature cataracts we cannot see through to the retina so we do an electrical test of the retina, the ERG (electroretinogram) to diagnose PRA.
Most cases of PRA end up developing cataracts. The degeneration retina releases factors that cause the lens to form cataracts. Initially the cataracts form on the back of the lens, with time the cataract matures. The mature cataract can leak lens protein; this can cause uveitis or inflammation of the eye. If untreated the lens/cataract induced uveitis can cause potentially painful conditions such as lens luxation or glaucoma.
It is very important to watch the white of the eyes for redness; this is the first sign of lens/cataract induced uveitis. If this inflammation is treated in the early stages with drops and/or tablets the risk of painful complications can be reduced.
Unfortunately there is no treatment for PRA as it is a genetic disease. In humans with various inherited retinal diseases have been treated with high doses of anti-oxidants, and lasers. However these treatments do not seem to be effective in dogs with PRA.
PRA is inherited as an autosomal recessive trait. This means that the condition is passed on from both parents. They may or may not show the disease, so always let the breeder know about the diagnosis.
If you are going to purchase a purebred dog that may be at risk of PRA, ask the breeder for eye certificates of both parents, and the grandparents. Responsible breeders will check their dogs before breeding.
In the near future a DNA blood test will be available to detect PRA at any age.
PROGRESSIVE RETINAL ATROPHY
PRA - Cataracts are secondary to PRA