Aussie Genetics Fact Sheet: Collie Eye Anomaly (CEA)
by C.A. Sharp
CEA is caused by a recessive gene mutation. Other, as yet unidentified, genes play a role in determining exactly what defects a dog will have, but without a double-dose of the mutated version of the one gene of major effect, a dog will not have CEA.
This means both sire and dam must carry the mutation to produce an affected pup. Production of a confirmed CEA puppy proves both stud and bitch are carriers. If a CEA puppy is produced, at least one grandparent on each side is a carrier, but there is no way to tell which, unless they have also produced CEA puppies.
Statistically, only 25% of the puppies from the breeding of two carriers will be affected. Carrier animals show no symptoms. There is no known relationship between CEA and coat or eye color. CEA has been identified in other dog breeds, including Collies, Shetland Sheepdogs and Border Collies. The CEA mutation is the same in all affected breeds.
A DNA test is available from OptiGen LLC that will determine the genotype of dogs who may be at risk for carrying CEA. Any breeding Aussie with a near relative that is either affected or a carrier of CEA should be screened with this test. It is possible on occasion to have both false positive and false negative results from an ophthalmic exam. If there is reason to doubt the accuracy of an exam report, the DNA test should be used to confirm or deny that result.
CEA affected puppies appear normal. The defects are within the eye and cannot be detected without special instruments. Positive diagnosis can only be made by a veterinary ophthalmologist or with the DNA test. The specific defects the examiner will note are choroidal hypoplasia (chorioretinal dysplasia), optic nerve coloboma/staphloma and, rarely, retinal detachment. Both eyes will be affected but the specific defects may differ from eye to eye.
Some CEA puppies are masked affecteds. (This was once called "go normal.") They appear normal on exam because normal pigment development in the back of the eye sometimes covers the defective areas preventing observation. Masked affecteds have two copies of the mutation. Any offspring they produce will be carriers. It is important that all puppies be examined no later than 8 weeks of age to get them properly diagnosed.
CEA is present at birth and does not progress. CEA puppies behave normally. Few will be so blind that the disease noticeably affects them. CEA does not cause the puppy any pain or discomfort. Affected animals should never be bred; but if they are not blind they can live happy and productive lives.