For the purpose of a health testing discussion, I will not try and discuss all possible eye disorders that a Mastiff have inherit. I will discuss the process (test) we have for testing: the CERF exam along with the PRA and CMR DNA testing.
In this entry, I will only discuss the PRA (Progressive Rential Atrophy) and the CMR (Canine Multi-Focal Retinopathy) diseases since they are the only eye diseases that we can currently DNA test for in Mastiffs.
Please note, that a CERF exam may also show other "genetic eye diseases"--i.e. Entropion, "cherry eye", Cataracts, Glaucoma, etc.- disorders that we DO NOT have DNA tests for at present in Mastiffs--so a CERF exam is essential to rule out genetic eye disorders.
Below is a labeled diagram of the canine eye. In the later discussions, you can use it as reference.
What is a CERF (Canine Eye Registration Foundation) Examination?
This database helps breeders and ophthalmologists monitor eye diseases. A CERF exam is basically the same exam you would get if you went to an ophthalmologist. A dog can be registered by CERFonce it has been examined by an ACVO diplomate and found to be unaffected by a major heritable eye disease.
CERF examinations are performed annually. The ophthalmologist fills out a computerized form and gives a copy to the owner. This copy can be sent to CERF by the owner (if the dog has been found to be unaffected, as previously described) along with the registration fee to receive a CERF registration number, which can be used by the owner for show purposes, breeding, and AKC pedigrees.
This registration is good for one year and it must be renewed annually by examination, to maintain an up-to-date CERF number. Since many ocular diseases do not appear until later in a dog's life, such as
progressive retinal atrophy and some forms of
cataract, it is suggested that an annual examinations be done to rule out heritable disease which occurs as a dog ages.
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.
CERF works with the ACVO genetics committee to determine ocular conditions that are identified with certain breeds. A book is available that lists all the known ocular disorders of dogs: Ocular Disorders Presumed to be Inherited in Purebred Dogs. It is updated as new information becomes available, and can be ordered from CERF.
What is Progressive Retinal Atrophy (PRA) in Dogs?
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.
It is recessively inherited in all breeds studied, with the following exceptions: PRA is dominantly inherited in Old English Mastiffs and Bullmastiffs, and PRA is sex-linked and found primarily in male dogs in the Siberian Husky and Samoyed breeds. In other words, for a Mastiff to inherit and manifest PRA, it must inherit a copy of the gene from only one parent.
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.
All dogs with PRA will eventually develop blindness from advanced PRA, and this time frame until the dog is blind varies considerably from dog to dog, but usually takes at least 6 months from the time of diagnosis, and can rarely take years until the dog is completely blind.
Although no treatment for PRA, nor is it possible to stop the disease. A nutritional antioxidant supplementation for retinal health may help slow the deterioration of the retina in some dogs to "buy some time" before the blindness inevitably happens. Holostic Animal Eye Care experts believe that in many of these PRA patients, specific oral antioxidant nutritional therapy can delay the progression of blindness.
However, Blindness can not be avoided in any PRA patients. If oral antioxidants were used, they would be continued until complete vision loss occurred.
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.
Dogs with PRA should not be bred, and the breeder that you received your dog from should be notified that the dog is affected, so the breeder can alter their breeding program in future.
It is important to understand that dogs with PRA are happy dogs. Their eyes don't hurt, and they adjust very well to their slow loss of vision. In fact, if a dog were destined to become blind and you could pick the disease, it would be PRA, as the vision loss is slow and nonpainful, and the dog is given much time to adjust to its vision loss.
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.
Your dog's job description has not changed. Your blind dog is happy as long as its routine is stable. From your dog's point of view, life continues to be great-- you are there as always, and they just need to use their other keen senses a bit more to get the same information they used to view. Keep household furniture in its place, and consider purchasing the book
"Living With Blind Dogs" by Caroline Levin. It is the only book of this subject matter, and is beneficial in helping owners and their affected pets adjust to the vision loss. It is suggested that you purchase a pet medical alert tags that reads, "I Have Poor Vision" or "I Am Blind" along with your address and contact info. Blind dogs have been known to wander away from home and be unable to find their way home.
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.
In the 1990's when PRA began to appear in Mastiffs, the MCOA along with the American Kennel Club Canine Health Fund help to set up and conduct a study which lead to the development of a DNA test for PRA. We now have a blood test available to determine if dogs are likely affected with PRA, are likely carriers for PRA, or are not likely carrying the PRA gene. Always ask a breeder if their dogs have had the DNA test for PRA.
In the table below, you can see how this disease is inherited:
What is Canine Multi-focal Retinopathy (CMR)?
CMR is a recently identified recessively inherited eye disease known so far to affect the Mastiffs (English, Bullmastiff, French mastiff or Dogue de Bordeaux), Great Pyrenees and Coton de Tulear. Early clinical studies in 1998 by Dr. Bruce Grahn at the University of Saskatchewan, Canada, first described CMR in the Great Pyrenees.
This condition was observed in each of the named breeds at an ophthalmologist’s exam that included numerous distinct (i.e. multi-focal), roughly circular patches of elevated retina with accumulation of material that produces gray-tan-pink colored lesions. These lesions, looking somewhat like blisters, often vary in location and size, although typically they are present in both eyes of the affected dog. Occassionally, Discrete areas of tapetal hyper-reflectivity might also be seen.
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.
And in almost all cases, CMR does not progress significantly over time. The disease seems to have a consistent pattern among the breeds identified so far, although lesions in the Coton de Tulear are often more serious and seem to remain longer than in some of the other CMR-affected breeds. In rare severe cases, the clinical diagnosis could be confused with progressive retinal atrophy (PRA). The full range of clinical symptoms will learned as more dogs are tested for their genetic status.
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.
(It should be noted that the human disease that mirrors CMR in dogs is an autosomal dominant disease with incomplete penetrance. This means that sometimes, but not always, only one copy of the disease gene needs to be present in order for the disease to be observed clinically.)
At this point CMR in dogs is NOT considered to be an autosomal dominant disease however as more animals are characterized genetically with the DNA CMR test, it is possible that we will find a similar form of inheritance as is seen in humans.
There is complete concordance of the mutation with the disease among affected dogs in the Mastiffs, Great Pyrenees and Coton de Tulear. However, retinal dysplasia described in other breeds, for example in Labradors, Samoyeds or English Springer Spaniels, is very distinct in comparison to CMR and these conditions are not caused by the CMR mutation.
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.
In the table below, one can see how breeding affected and carrier dogs produced this disease.
