by Catherine McMillan

Retinal dysplasia is a congenital defect that occurs when the layers of the retina do not form and attach properly during fetal development. The extent of the dysplasia can vary widely in individual dogs, ranging from very subtle folds in the retina to complete retinal detachments that cause total blindness. The majority of affected dogs fall somewhere in
the middle and few exhibit any signs of vision problems.

PHPV (persistent hyperplastic primary vitreous) is often, but not always, diagnosed in Miniature Schnauzers with RD.

While RD is not a progressive disease, the retinas of even mildly affected dogs are unstable and can detach later in life. Affected dogs may also develop secondary cataracts and glaucoma, and must be monitored through their lifetimes for these conditions.

Treatment:
Laser surgery has been useful in mild to moderately affected dogs to help stabilize the retina and prevent detachments. In severe cases involving glaucoma, affected eyes may require surgical removal to relieve pain. However, Miniature Schnauzers who are blind from this condition adapt well to their surroundings, and many live happy lives as pets.

Inheritance:
Research has established that retinal dysplasia in Miniature Schnauzers is caused by a simple autosomal recessive gene (inherited from both parents). The only way to diagnose RD is through a puppy eye exam by a veterinary ophthalmologist. Pedigree analysis based on reported cases suggests the gene has been present in the gene pool since at least the early 1970's and not confined to any one family line.

While it is possible for RD to be due to other causes (eg. viral infections during pregnancy), published data from CERF (Canine Eye Registration Foundation) suggests that environmental cases of RD must be relatively rare. (The same yearly reports also suggest that RD occurs in the breed at about the same frequency as PRA.)

Reducing the Risk:
Buyers of Miniature Schnauzers can ensure that they do not purchase a pet with this defect by insisting that their puppy receive a routine eye exam by a veterinary ophthalmologist prior to taking it home. RD is a congenital defect and present at birth. There is no risk of a normal eyed puppy developing inherited retinal dysplasia later in life.

While research into a DNA test for retinal dysplasia is in progress, breeders have also employed test breeding as a tool to identify carrier and clear animals in their breeding programs. Breeders who encounter this defect in a litter are urged to contact the AMSC health committee for recommendations and referral.

For more information: http://www.vetcontact.com/en/art.php?a=292&t