What is Collie Eye Anomaly (CEA)?
CEA is a disease of the vascular and nerve tissues in the back of the eye. The most common defect is choroidal hypoplasia (CH), also called chorioretinal dysplasia, a thinning of the vascular tissue that lies between the retina and the wall of the eyeball. Every dog with CEA has H in both eyes. Some dogs also have optic nerve coloboma, in which a portion of the optic nerve where it enters the back of the eyeball has failed to develop. Another less common CEA defect is retinal detachment.
How do I know if my dog has CEA?
In most cases you won’t know without an exam by a veterinary ophthalmologist, thoughoccasionally a puppy will be blind.
Why do you have to check all puppies producd and check them at a young age?
If at least one parent has CEA tested clear it isn’t necessary. But if that is not the case an early puppy eye screen is vital. CEA can be tricky to catch. If you don’t check all the puppies in every litter, you may miss the affected ones. If they aren’t checked young, they may become masked affecteds (once referred to as “go normals”) and be indistinguishable from unaffected dogs. If a puppy is a double merle you won’t know because the eye defects typical in dogs that inherit two copies of the merle gene will make it impossible to recognize CEA for what it is. Ideally, puppy exams should be done before 6 weeks of age to be sure they are checked before any might become masked affecteds. A puppy eye exam can also detect other congenital and inherited eye defects for which we do not have DNA tests.
What is a masked affected?
A dog that has CEA that can’t be detected in an eye exam is a masked affected. These dogs do have the disease; they just can’t be diagnosed by eye exam. If a dog has only choroidal hypoplasia sometimes the natural pigment in the back of the eye hides its presence. The pigment is not present in young puppies but starts to fill in at about 6 weeks.
What does having CEA mean for my dog?
CEA causes no pain or discomfort, but it can impact vision. Most dogs with CEA have only choroidal hypoplasia and their vision is functional. Optic nerve coloboma can reduce vision and very large colobomas can leave the dog blind in the affected eye. Detached retinas are also blinding. Dogs that are blind in one eye can function well but can be at risk from hazards that arise on their blind side; activities like agility and stockwork may be ill advised. If a dog is totally blind it can live a good life though certain activities won’t be possible and it will need to be protected from hazards it cannot see. The senses of smell and hearing are more important to a dog than vision and most dogs adjust well, particularly those blind from birth as would be the case if the dog had CEA.
Is CEA inherited?
Yes, the gene which causes choroidal hypoplasia has been located and the mutation is recessive. Since all dogs with CEA have CH it can be managed in the same way one would manage any single gene recessive trait even though other as-yet unidentified genes cause the more serious defects.
How common is CEA in Aussies?
Around 1% are affected. It is likely that somewhere about 10% are carriers.
How likely is it that a normal littermate to a puppy with CEA carries the gene?
Every normal full sibling of a dog with CEA has a 2 in 3 chance of being a carrier.
Is there a DNA test for CEA?
Yes. It tests for the gene mutation that causes choroidal hypoplasia which is present in all CEA dogs. Results will indicate whether your dog has one, two, or no copies of the mutated version of the CEA-CH gene. Dogs with two copies are affected, whether or not they have clear eye exams (see the question about masked affecteds, above). Dogs with one copy of the mutation are carriers. If your dog does not have the mutation it is clear of CEA.
What dogs should be tested?
Given that about one in 10 Aussies is a carrier it would be a good idea to test all breeding dogs for CEA unless bothh of its parents have tested clear.
What does CEA mean for my breeding program?
With the DNA test CEA can easily be managed in your breeding program without fear of producing more affected pups. Do not breed affected dogs and breed carriers only to clear-tested mates. Give preference to clear-tested offspring to carry on with. No male that is a CEA carrier should be used extensively at stud.