Collie Eye Anomaly (CEA) CEA is a congenital disorder where the parts of the eye, particularly the retinal area, do not develop normally. The severity of the disease ranges from no visual impairment to blindness. It is not a progressive disease and affected dogs normally only have mildly impaired vision. Puppies should be tested before 12 weeks of age, if possible, by a Diplomate of the Association of Canine Veterinary Ophthalmologists (DACVO) because some dogs have a mild form of the disease called "go normal", where normal tissue grows over and covers up the diseased area as the dog matures. Identification of "go normals" is important, as these dogs are affected with CEA and will produce affected puppies just as if they had full blown expression of the disease.
This disease is much more straightforward than HD in both its inheritance patterns and in our ability to control it. CEA is an autosomal recessive disorder. Autosomal means it is passed on and expressed equally in males or females. Recessive means a dog may carry a bad CEA gene and pass it on to its offspring without having the disease itself. A dog is defined as Clear if it has no bad CEA genes. A dog is defined as a Carrier if it has one bad CEA gene and one normal gene. Both the Carrier and the Clear dogs will be unaffected and will test negative for CEA in the eye exam. A dog is defined as Affected if it eye tests positive for CEA. The outcomes of the different crosses of these dogs are as follows:
Clear X Clear = 100% CEA Clear puppies
Clear X Carrier = on average, 50% Clear, 50% Carriers
Clear X Affected = 100% Carriers
Carrier X Carrier = on average, 25% Clear, 50% Carriers, 25% Affected
Carrier X Affected = on average, 50% Affected, 50% Carriers
Affected X Affected = 100% Affected
The incidence of CEA in Border Collies in North America is about 2.5%. The carrier rate is probably ten times that figure, or 25%. The problem in controlling the disease at this time is that the only way to know if a dog is a Carrier is for it to produce an Affected puppy. Since there are many unknown Carriers out there, Affected puppies will inadvertently be produced until we have a better way to test for Carriers.
The ABCA, with support from other working Border Collie groups and owners, has funded Dr Gregory Acland from the James A. Baker Institute for Animal Health, Cornell University, to develop a DNA test for CEA. This test will identify the CEA clear dogs (those with no bad CEA genes). The test is now available!