Retinal Dysplasia in Cavalier King Charles Spaniels
Hereditary eye disease has become widespread in the cavalier King Charles spaniel. A study of CKCSs conducted by the Canine Eye Registration Foundation in 1999 showed that an average of 30% of all cavaliers evaluated had eye problems.
The most serious eye defects that afflict high percentages of cavaliers are forms of retinal dysplasia. Retinal dysplasia is a malformation of the retina. It occurs when the two layers of the retina do not form together properly. Mild dysplasia appears as "folds" in the inner retinal layer, called retinal folds. In "geographic" retinal dysplasia there are larger areas of defective retinal development. In the severe form of dysplasia, known as retinal detachment, the retinal layers do not come together at all.
Retinal folds represent small blind spots which are probably not even noticed by the dog. However, geographic dysplasia may lead to large deficits in the visual field, and cavaliers with retinal detachments are completely blind.
The cause of retinal dysplasia in cavaliers is genetic. Of all purebred dogs, multifocal retinal dysplasia (MRD) and geographic retinal dysplasia are most commonly found in the cavalier King Charles spaniel, according to Dr. Sheila M. Crispin, MA, VetMB, BSc, PhD, DVA, DVOphthalmology, MRCVS, DipECVO, of the School of Veterinary Science, University of Bristol, UK.
Diagnosis
All CKCSs should be examined by a board certified veterinary ophthalmologist to determine whether the dogs have retinal dysplasia, and if so, the type and degree of it. Board certified veterinary ophthalmologists are listed on the website of the American College of Veterinary Ophthalmologists (ACVO). Upon examination, the ophthalmologist can tell the degree of severity of the dysplasia. Most cases of retinal dysplasia do not progress after puppyhood, and the ophthalmologist may be able to predict the extent to which the dysplasia will interfere with the dog's field of vision.
Breeders' Responsibilities
The Genetics Committee of the ACVO classifies the mildest form of retinal dysplasia (retinal folds) as a "breeder option" for CKCSs. Therefore, the Canine Eye Registration Foundation (CERF) does not deny certification to cavalier King Charles spaniels which are affected with the disorder of retinal folds. However, both the Genetics Committee of the ACVO and the Canine Inherited Disorders Database recommend that CKCSs affected with geographic and retinal detachment forms of retinal dysplasia not be bred. Any littermates of breeding stock having retinal dysplasia should be taken into consideration.
The Cavalier King Charles Spaniel Club, USA recommends that, prior to breeding any cavalier, the dog have a normal rating or be within CERF "breeder options" from a screening by a board certified veterinary ophthalmologist.
The Canine Health Information Center (CHIC) is a centralized canine health database sponsored by the AKC/Canine Health Foundation (AKC/CHF) and OFA. The CHIC, working with participating parent clubs, provides a resource for breeders and owners of purebred dogs to research and maintain information on the health issues prevalent in specific breeds.
AKC's national breed clubs establish the breed specific testing protocols. Dogs complying with the breed specific testing requirements are issued CHIC numbers. The ACKCSC requires that, to qualify for CHIC certification, cavaliers must have a CERF eye examination, recommending that an initial CERF exam be performed at 8 to 12 weeks, with a follow up exam once the dog reaches 12 months, and annual exams thereafter until age 5 years, and every other year until age 9 years.
All cavalier breeding stock should be examined by board certified veterinary ophthalmologists at least annually and cleared by the veterinary specialists for all but the mildest form (retinal folds) of retinal dysplasia, the closer the examination to the breeding the better.
Current Research
4The Animal Health Trust (AHT) is conducting research to try to establish the pattern of inheritance of CKCSs with multifocal retinal dysplasia (MRD). Dr. Keith Barnett OBE MA PhD BSc DVOphthal FRCVS DIpECVO, European Specialist in Veterinary Ophthalmology, is leading a team of AHT colleagues who are researching the DNA of such cavaliers. According to Dr. Barnett, cavaliers could benefit from the MRD research in Golden Retrievers, where it is hoped that the gene marker responsible for the condition will soon be identified, and that cavaliers may possess a similar marker. Dr. Barnett believes his team has identified the chromosome responsible for MRD, but they still are searching for the gene.
Dr. Barnett requests that breeders who have CKCSs affected with MRD send blood samples from the affected dogs and their unaffected siblings, parents, and close relatives to identify the responsible gene. Contact Dr. Barnett at the AHT if you wish to participate in the research project. He may be reached at Animal Health Trust, Lanwades Park, Kentford, Newmarket, Suffolk CB8 7UU, United Kingdom; telephone: (+44) (0)8700 502424; email: Keith.Barnett@aht.org.uk Blood samples of 3 to 5 ml should be provided in ETDA anti-coagulant tubes. Alternatively, for very young or old donors, cheek swabs may be used. Samples should be marked for the attention of Dr. K. Barnett and sent to: Sarah Gray, The Animal Health Trust, Lanwades Park, Newmarket, Suffolk CB8 7UU UK. Please indicate clearly whether the samples are MRD pass or failures and the name of the Ophthalmologist who conducted the diagnosis.
4Canine Multi-focal Retinopathy (CMR) is a inherited eye disease known thus far to affect Great Pyrenees, Mastiffs and Coton de Tulear. Dr. Bruce Grahn of the University of Saskatchewan, Canada, first described CMR in the Great Pyrenees. A DNA-based test that reportedly accurately diagnoses multi-focal retinopathy occurring in these breeds has been developed and is being administered by OptiGen. The test also reportedly detects carriers of this condition and clears dogs that are genetically normal. For more information, see this page of the OptiGen website: www.optigen.com/opt9_test_cmr.html
Related Links
American College of Veterinary Ophthalmologists (ACVO)
Veterinary Resources
Control of Canine Genetic Diseases. Padgett. G.A., Howell Book House 1998, pp. 198-199, 242.
Ocular Disorders Presumed to be Inherited in Dogs. A.C.V.O. 1999.
The geographic form of retinal dysplasia in dogs is not always a congenital abnormality. Holle, Stankovics, Sarna, Aguirre. Vet. Ophthalmology; 2:1 (61-66) Mar 1999.
Guide to Congenital and Heritable Disorders in Dogs. Dodds WJ, Hall S, Inks K, A.V.A.R., Jan 2004, Section II(270).
Breed Predispositions to Disease in Dogs & Cats. Alex Gough, Alison Thomas. 2004; Blackwell Publ. 44-45.
Notes on Veterinary Ophthalmology. Crispin S.M. Blackwell Publ. 2005.
Ophthalmic Disease in Veterinary Medicine. Martin C.L. Manson Publ. 2005.
Canine Inherited Disorders Database: http://www.upei.ca/~cidd/Diseases/ocular%20disorders/retinal%20dysplasia.htm
Breed Predispositions to Disease in Dogs & Cats (2d Ed.). Alex Gough, Alison Thomas. 2010; Blackwell Publ. 54.
