A
diagnosis of PRA generally means that your dog has one of a group of
related, hereditary diseases of the retinal visual cells. These
diseases are characterized by malformation or degeneration of the
retina. These diseases are incurable and, as the disease
destroys the retina of the eye, affected dogs will eventually become
blind.
Even though clinical
signs are the same in all genetically affected PRA dogs, the age of
onset of disease will differ from breed to breed.
In
some breeds, vision loss may be seen in young puppies with complete loss
of vision before or soon after maturity. In other breeds, the
disease may not be diagnosed until dogs are 1-5 years old. The
late-onset form of PRA, generally diagnosed between 3 and 6 years of
age, is called Progressive Rod-Cone Degeneration (PRCD). PRCD is
especially devastating to future generations of the affected breed.
With the late-onset form of disease, affected dogs (especially
well-known titled dogs) may have already been bred numerous times before
the disease is diagnosed. The puppies produced in this
subsequent generation will, at a minimum, ALL be "carriers" of the
defective PRA gene. Many pups may be affected and these dogs
will all have the potential for further reproducing this defect.
Retinal degeneration can be due to non-PRA causes. If diagnosed
early, non-PRA retinal degeneration can be distinguished from genetic
PRA retinal degeneration. Routine eye
examinations of all breeding stock by a canine ophthalmologist are
advised in all breeds so that retinal degeneration can be promptly and
properly identified. If your show/breeding stock dog should be
diagnosed with PRA, it's always a good idea to get a second opinion.
A determination of PRA can be
subjective and you don't want to throw away your investment in the
dog by neutering or spaying until you're absolutely sure there is cause.
Most forms of PRA are caused by autosomal recessive gene defects.
Dogs affected with PRA have 2 defective PRA genes. This means
that dogs diagnosed with PRA received a recessive, defective PRA
gene from each parent. This does not mean that each parent is
affected by PRA. It merely means that each parent at least CARRIES one
copy of the same recessive, defective gene. Both parents could have normal
eyesight, but if they each carry a hidden, defective PRA gene,
then the two defective genes may be inherited by one or more puppies in
any litter. Puppies that inherit a defective gene from each parent
will then be PRA affected and will eventually go blind. For more
information on the inheritance of autosomal recessive genes, you can go
to my 
page.
Symptoms of
PRA may go unnoticed until the disease is well advanced. Symptoms
could include signs of night blindness, followed by gradual loss of day
vision and, eventually, the loss of all vision. Due to the gradual
nature of the vision loss, many owners are unaware of a problem until
the dog is examined by a canine ophthalmologist. Most dogs will
compensate for their gradual loss of sight by depending more heavily on
their sense of smell, touch and hearing. Most affected dogs
will cope
quite well with impaired vision and even total blindness. As
long as the dog is in familiar surroundings, it's often impossible to
tell that a dog suffers from blindness or impaired vision.
At
this time, the most widely available diagnostic tool for PRA is your
canine ophthalmologist. A certified canine ophthalmologist
can diagnose PRA with electro-retinography testing. It must be
understood that this testing only identifies "affected" dogs (those with
2 defective genes) that are already exhibiting symptoms of the disease.
This testing cannot identify dogs that have 2 defective genes but are
not exhibiting symptoms of disease nor can it identify clinically normal
"carriers" of one recessive, defective PRA gene.
Scientists have
perfected DNA testing for one form of PRA in Cockers, but this test does
not identify carrier or affected dogs with other forms of PRA.
While this is a tool that is bound to help breeders identify and
eliminate the specific form of PRA that can now be tested for, it will
probably be quite a number of years before we see significantly fewer
carrier and affected dogs within the gene pool. This is because,
at the moment, the test is prohibitively expensive for most breeders
($250 per dog + the cost of having a veterinarian pull and ship a blood
sample - approximately $50 additional) Hopefully this new testing
will become more affordable over the next few years and more breeders
will be able to screen their breeding dogs for this form of PRA. This would be a
huge step forward for our breed and breeding programs.
Remember, all
breeding stock should have annual eye exams by a licensed canine ophthalmologist.
