What is a CERF (Canine Eye Registration Foundation) Examination?
The Canine Eye Registration Foundation (CERF) was established in 1974 to track heritable eye diseases in purebred dogs. A database is maintained through registered purebred dogs examined by board certified veterinary ophthalmologists (Diplomates of the ACVO -- American College of Veterinary Ophthalmologists).
In an effort to educate the public, CERF also publishes a quarterly newsletter about eye diseases in dogs. It contains current information about the frequency and heritability of eye diseases in dogs, and gives tips for healthy breeding practices. This publication is a great source of inform,ation for dog owners and breeders.
The goal of CERF is to identify those conditions that should be selected away from when breeding. To simplify, dogs with bad hips should not be bred, and dogs with inherited cataracts and certain other eye diseases are not suitable for breeding either. Other problems result from facial conformation considered desirable by breeders. For example, breeding for prominent eyes and facial folds in Mastiffs might lead to corneal irritation, scarring, and eventual blindness.
This is a genetic, inherited disease of the retina (the "film" in the camera), which occurs in both eyes simultaneously. The disease is nonpainful, and there is no cure for it. The eyes are genetically programmed to go blind. PRA occurs in most breeds of dogs and can occur in mixed breeds also.
Clinical signs vary from the dog first becoming night blind in the early stage of PRA (not able to see in low light surroundings) to the entire visual field in all light levels becoming affected, which is advanced PRA. The pupils are usually dilated, and owners often notice a "glow" and increased "eye shine" from the eyes.
What Should I do if I suspect My Mastiff has PRA?
As with any serious eye disorder, have your dog examined by a board certified veterinary ophthalmologist to determine if this disease is indeed present. Your local Vet can refer you to the closest Canine opthalomigy specialist fo an ophthalmic examination.
It is important to realize that it is OK to grieve about your pet's vision loss, but you must not put your sad feelings in your dog's head--they aren't really there! Your dog is not suffering. They adjust well to their vision loss, and it is by far hardest to deal with on the owner's side.
Dogs with PRA can develop cataracts late in the disease process. Cataract surgery would never be done, as it would not help the dog to see. However, cataracts can cause pain and damage to the eye, and if the eyes look very cloudy to you, please call your opthomoligist vet for a reexamination as soon as possible.
The disease generally develops in young dogs before 4 months and might progress slowly, might even appear to heal, or might even appear and then go away again. Some lesions disappear with no remaining sign, while some lesions leave a wrinkled area – a fold. Some leave the lasting lesion of a blister formation. Most dogs exhibit no noticeable problem with vision despite their abnormal appearing retinas.
The clinical presentation and pathology of CMR closely resembles lesions of “Best vitelliform dystrophy”, a human disease with variable clinical expression but usually with serious affects on central vision. Identification of the gene mutation responsible for CMR was based on these similarities. A mutation in the human VMD2 gene – Vitelliform Macular Dystrophy 2 Gene – causes dominantly inherited human Best Disease. Analysis of the canine version of the VMD2 gene indicates that mutations in it cause CMR as a recessively inherited canine condition. The normal form of the VMD2 gene produces a protein named “bestrophin”. The bestrophin protein assembles, in the cells of the retinal pigment epithelium, in a group of four or five units that form a pore through which chloride ions pass.
Our current understanding is that CMR in Mastiffs is inherited in an autosomal recessive pattern. This means the gene mutation responsible for CMR is located on an autosome (that is, a chromosome that is not a sex chromosome) and CMR disease results when the gene mutation is passed to the offspring by both the mother and the father.
Due to the abnormal appearance of the CMR-affected retina, CERF, ACVO, ECVO and other ophthalmologist’s eye exam reports typically record these multi-focal lesions as “retinal dysplasia” or “retinal folds”, to denote a defect in formation of the retina. Such findings might disqualify the dog from breeding. Presently CERF doesn’t list CMR as a specific condition, but does fail a dog for “retinal dysplasia/retinopathy – folds, detached.”
The genetic test for CMR is valuable for identifying Mastiffs affected and those which are carriers. Given the exact genetic diagnosis, a breeder can identify carriers and breed only to "clear" dog--thus no "affected" puppies will be produced. Puppy buyers who purchase a "carrier" puppy can be assured that there probably will be no vision loss due to this condition. By using the DNA CMR test and eliminating Carriers and affected dogs from our breeding programs, future cases of the condition can be prevented.