Although retinal dysplasia is congenital-that is, present at birth-it cannot be diagnosed until the eye is somewhat mature. Breeders must wait until the litter is seven to eight weeks old before a proper examination can take place. However, that’s still enough time to find out whether the puppies have the disease before they become an integral part of a new family.

Normal vs. Abnormal

The normal retina has 10 anatomical layers arranged in even rows of equal size and density. A three-cell pyramid (consisting of rods and cones, bi-polar cells and ganglion cells) transmits an electrical impulse to the optic nerve, which in turn travels to the brain. In the brain, the electrical impulse is recorded as sight.

In the case of retinal dysplasia, however, the normally smooth retinal surface forms tubes. The retinal pigment epithelium (the deepest layer of the retina) may also be defective or atrophied. Once present, the condition does not progressively worsen unless retinal detachment occurs, in which case complete blindness is the result.

Although only one eye may be affected, retinal dysplasia usually occurs bilaterally. The defects are not necessarily identical in the right and left eye. However, it is believed that bilaterally affected dogs with differing defects can compensate to a certain degree for their disability.

Thus, dogs may suffer from a wide range of visual loss possibilities. Those with minimal defects, especially if only one eye is affected, learn to compensate visually with their normal eye, and so they function rather well. Other dogs are totally blind. Most individuals, however, fall somewhere between the two extremes.

Dogs with partial loss of sigh are thought to have discrete blacked-out areas within their visual field while sight is normal elsewhere. For instance, if a dog with partial loss of sight was watching a passing car, the affected retinal area may cause him to see a black area where the door is located. This black area represents that particular dog’s area of visual loss. Another affected dog viewing the same car might not see a tire, a door handle, the back bumper or, worst of all, the entire car.

Retinal dysplasia is diagnosed using direct or indirect ophthalmoscopy. With indirect ophthalmoscopy, the pupil is first dilated and then viewed by the veterinarian through special illumination and a magnification lens. Using this technique, the retina appears upside down and backwards; about 40 to 50 percent of the retina is visible at a glance. This enables a thorough exam to be completed quickly.

Direct ophthalmoscopy is performed with an ophthalmoscope in place of a light and lens combination. This produces a what you see is what you get type of exam, with only 5 percent of the retina observable at any one time. Therefore, the scope must be repositioned many times in order to examine the entire retina. In the hands of a qualified veterinary ophthalmologist, either technique is adequate for a diagnosis.

The affected areas of the retina appear to the trained eye in the form of streaks, or gray or green dogs. In some breeds (i.e., field trial Labs and English Springer Spaniels), large areas of retinal dysplasia may be present. Dogs with retinal dysplasia may also have other concurrent eye disorders and systemic anomalies of the nervous, cardiac or skeletal systems.

Although a veterinary ophthalmologist can determine whether a dog is affected with retinal dysplasia, he or she cannot provide an exact assessment of what the dog can or cannot see. Owners often devise their own tests to determine the extent of their dog’s vision (for instance, can he see an object 50 yards away? 100 yards? Can he see a stationary object, but not a moving one?). Such tests at least give owners some idea of the dog’s limitations. Many find that dogs possessing partial vision often adjust remarkably well to their disability. A Labrador with minor vision loss, for example, may be able to see most of the birds his master shoots from a duck blind. But this vision loss is probably enough to eliminate the same dog from field trial competition, where superb vision is critical for success.

Ocular examinations are particularly important for dogs used in breeding programs to ensure that new problems, or existing ones previously gone undetected, are prevented from being passed on to new generations. Even though an early exam will rule out heritable retinal dysplaysia, for the best level of care, dogs should be reexamined annually. This would detect a case of retinal dysplasia caused by certain diseases, such as toxoplasmosis, as well as other ocular problems. Retinal dysplasia caused by an infection does not, of course, affect the dog’s genetic disposition towards the disease.

Also, CERF requires annual examinations for continuing certification, as other diseases can and do develop during an individual’s lifetime.

Heredity and Other Causes

Retinal dysplasia is generally believed to be inherited as a simple autosomal recessive trait (with Labradors, it may be either simple autosomal recessive or dominant with incomplete penetrance). Recessive heritability means the sire and dam of the litter are each heterozygous for the trait and therefore should not be bred, either to each other or to other dogs. Within an affected litter, there may be some puppies that show the disease and others that do not. Even unaffected pups in such a litter have a 67 percent probability of being heterozygous. All puppies from a litter that contains even one affected pup should be spayed or neutered, in order to prevent passing the trait on to future offspring.

Only careful and responsible breeding will reduce and eventually eliminate retinal dysplasia. Affected or potential carriers should go to pet homes and spay/neuter contracts, with the new owners fully informed of the dog’s limitations.

Although a hereditary factor is the most common cause of retinal dysplasia, the disease may have other etiologies. These include trauma, viral infection such as canine herpesvirus, irradiation, and the administration of various drugs. These events can occur during gestation or early puppyhood.

However, heredity may be differentiated from other causes of retinal dysplasia at the time of diagnosis based on ophthalmic and historical findings. For example, dysplasia attributable to a viral infection seems to be characterized by retinal atrophy and gliosis (fat surrounding the nerve fibers). Irradiation, on the other hand, causes folds and rosettes to form on the retina, along with a reduction of the number of small retinal vessels and a narrowing of the larger ones. Large vessels also tend to have a dull appearance, as opposed to the bright color associated with normal retinas. Retinal dysplasia due to irradiation always occurs in both eyes.

Summary

Retinal dysplasia is a heartbreaking diagnosis. It can mean the end to a promising show career or future as a brood bitch or stud dog. It can prevent dogs from participating in field events or performing the function for which they were bred-or from just enjoying a full life. And any puppy owner would naturally be shattered to learn that the dog he or she has come to love suffers from permanent vision loss.

Now what? The breed ring is an arena for showing potential breeding stock. What should breeders do if a beautiful dogs has perfect vision, but is heterozygous for retinal dysplasia? And how about the dog with an outstanding performance record? Who could resist breeding such dogs?

You should. It may not be long before the progeny of these dogs can’t find the dumbbell or gauge the distance to a jump in the obedience ring. Are we prepared to deny future generations of their heritage, whether it’s the ability to herd, retrieve, or course prey? Hopefully, dog lovers will never be ready for that day.

Responsible breeders should diligently pursue early examination of puppies along with the elimination of affected or potential carriers dogs from their breeding programs. With the spaying and neutering of dogs unsuitable for breeding, regardless of their show or performance records, there is hope that retinal dysplasia can someday be eliminated.

The Canine Eye Registry Foundation (CERF) was founded by concerned breeders in 1974. Now affiliated with Purdue University, CERF has established a veterinary medical data base (data is compiled from 22 participating veterinary colleges in the U.S. and Canada) which is used for researching trends in eye disease and breed susceptibility. CERF’s goal is to eliminate heritable eye disease in pure-bred dogs by forming a centralized, national registry.

To obtain a CERF registration number, a dog must be certified free of heritable eye disease by a member of the American College of Veterinary Ophthalmologists (ACVO). Dogs and puppies can be certified as soon as the eye is physically mature enough to undergo the painless examination, usually at five to six weeks (seven to eight weeks is considered a reasonable time to examine for retinal dysplasia). Animals must have an individual registration number for certification. Certification is valid for 12 months. Dogs must be reexamined and certified annually to maintain CERF registration.

Breeders are encourage to contact CERF for breeding advice, which is based on guidelines established for their particular breed by the Genetics Committee of ACVO (CERF and ACVO are separate, cooperating entities).

CERF welcomes phone calls from fanciers for public information ranging from availability of local ACVO members, published materials on eye disease, questions about specific diseases and verification of CERF status on individual dogs. Their number is (317) 494-8179.