Canine Multifocal Retinopathy (CMR): Causes, Risks & Testing

Canine Multifocal Retinopathy (CMR) is an inherited eye condition that causes multiple raised retinal lesions, often visible by 4 months of age. This genetic disease, caused by gene mutations affecting the retinal pigment epithelium, can lead to retinal folds and in some cases, retinal detachment.

Because CMR is hereditary and passed recessively through genes such as VMD2 and Bestrophin 1, responsible breeding practices are critical. DNA testing before mating helps breeders avoid producing affected litters, supporting healthier future generations and reducing the spread of this condition.

Understanding Canine Multifocal Retinopathy

CMR typically appears in puppies just a few months old. Lesions appear as pinkish-grey, irregularly shaped spots in both eyes and may or may not worsen over time. Some dogs experience stable symptoms with no vision loss, while others may develop mild visual impairment; complete blindness is rare.

Multiple forms of CMR exist, notably CMR1 and CMR2, each caused by different genetic mutations but showing similar clinical signs. Long-term vision prognosis is generally good, with many dogs maintaining normal sight despite the retinal changes.

Genetic Inheritance and Breeding Implications

The condition is autosomal recessive, meaning a dog must inherit two copies of the faulty gene to be affected. Each parent dog’s status is classified as clear (no mutation), carrier (mutated gene but unaffected), or affected (mutated gene with clinical symptoms).

Depending on parental genetic status, the possible outcomes for puppies are predictable:

• Two clear parents: all pups clear.
• Two affected parents: all pups affected.
• Two carriers: 25% clear, 50% carriers, 25% affected pups.
• One clear and one carrier: 50% clear, 50% carriers.
• One clear and one affected: all pups carriers.
• One carrier and one affected: 50% carriers, 50% affected.

Breeds at Higher Risk of CMR

CMR has been identified in various dog breeds, and DNA testing is recommended before breeding. Breeds with higher risk include:

• Bullmastiff puppies
• English Mastiff puppies
• Australian Shepherd puppies
• American Bulldog puppies
• French Bulldog puppies
• English Bulldog puppies
• Cane Corso puppies
• Dogue de Bordeaux puppies
• Pyrenean Mountain Dog puppies

Testing and Responsible Ownership

Genetic testing via blood or cheek swab is essential to identify if a dog is clear, carrier, or affected by CMR. This testing helps breeders select healthy mates and avoid passing the condition to puppies.

For prospective puppy buyers, requesting to see the results of parental genetic tests assures choosing puppies less likely to be affected or carriers. This supports ethical purchasing decisions and promotes overall breed health.

Managing CMR in Affected Dogs

While CMR usually does not cause major vision loss, regular veterinary check-ups with a specialist ophthalmologist are advised to monitor retinal health. Early detection and supportive care help maintain quality of life for affected dogs.

Owners should maintain a safe environment to help dogs with any vision impairment navigate comfortably. Good nutrition, exercise, and attentive veterinary care contribute to long-term well-being.

Conclusion

Canine Multifocal Retinopathy is a genetically inherited eye disorder affecting several dog breeds. Thanks to advances in DNA testing, breeders can now prevent the spread of CMR by responsible mating choices. Buyers should favour pups from tested parents.

Awareness and genetic screening not only safeguard dogs’ vision health but also enhance the welfare of future generations. Regular veterinary ophthalmic evaluations are key for affected dogs to manage symptoms and preserve quality of life.