Collie eye anomaly (CEA) is a congenital, developmental defect of the eye. The disease has been reported in rough and smooth collies, Shetland sheepdogs, Australian shepherds and border collies. It was first described by Magrane in 1953 in the United States(*1) and has become very widespread in the collie breed. In the 10-year period from 1991-1999, 19,592 collies were reported to CERF by ophthalmologists and about 15,000 (77%) of these had some form of CEA. The incidence is lower in other affected breeds.
Collie eye is due to an abnormal development of the mesodermal (middle layer) tissues of the eye. This results in defects of the sclera, choroid, optic disk, retina and blood vessels of the retina. These defects can be very extensive and lead to blindness or they can be relatively minor and cause no visual deficits.
The most common form of CEA is choroidal hypoplasia (CH). This is a defect in the choroid or vascular system of the back of the eye. It can be seen in an ocular examination as a non-pigmented area beside the optic disk. Although CH causes no problems for vision it indicates that the affected dog carries the gene(s) for CEA. CH is a bilateral disease but one eye may be more affected than the other. The area involved is usually above and to the side of the optic nerve. Lesions of CH can be seen at 5 to 7 weeks of age but later can become masked by the development of pigment in the back of the eye as the dog ages. These cases are called "go-normals." It is because of these cases that it is important to examine puppies at a young age. Even though these dogs may appear normal as adults, they still are carrying the gene for collie-eye. CH does not become worse nor does it progress to any other type of CEA.
More severe cases of CEA usually have colobomas. In CEA, colobomas are depressions or excavations in the back of the eye and may involve the optic disk and/or the area around the optic disk. Colobomas may be seen by an ophthalmologist in puppies as early as 5 to 7 weeks of age. Colobomas may involve one or both eyes and may be very small and shallow or extremely large and deep.
Partial or total retinal detachments may be present in some cases of CEA. These may be unilateral or bilateral and usually develop in young puppies and cause complete blindness. Large optic disc colobomas can cause retinal detachment because the large "hole" in the back of the eye leads to accumulation of fluid behind the retina and pushes off the retina. Bleeding in the back of the eye can also occur in CEA and is thought to be secondary to colobomas and retinal detachments.
CEA is a known hereditary disease and is thought to be due to an autosomal recessive gene(*2). The site of the gene causing collie eye is currently being investigated(*2). Because of its hereditary nature, the policy of CERF is to recommend that any dog with CEA (of any severity) not be bred and affected dogs will not receive a CERF number. We hope that in the future a genetic test will be available to detect both affected and carrier animals and that this will help reduce the incidence of this disease.