Issue Description A congenital, inherited, bilateral eye disease
of dogs involving the retina, choroid, and sclera. It can be a mild
disease or cause blindness. CEA is caused by a simple autosomal
recessive gene defect. Other Names Collie Eye Anomaly
Causes CEA is caused by improper development of the
eye. Failure of the cells of the posterior portion of the optic
vesicles to express growth hormone affects the differentiation of
other cells of the eye. The choroid, especially lateral to the optic
disc, is hypoplastic (underdeveloped). A coloboma, or hole, may form
in or near the optic disc due to a failed closure of embryonic tissue.
The degree of these abnormalities varies between individual dogs, and
even between the same dog's eyes. CEA is inherited as an autosomal
recessive trait that has a penetrance reaching 100 percent, and has
been located to canine chromosome 37.
Breeds Affected It is known to occur in Smooth and Rough
Collies, Shetland Sheepdogs, Australian Shepherds, Border Collies,
Lancashire Heelers, and Nova Scotia Duck Tolling Retrievers. Frequency
is high in Collies and Shetland Sheepdogs, and low in Border Collies
and Duck Tollers. In the United States, incidence in the genotype of
collies has been estimated to be as high as 95 percent, with a
phenotypic incidence of 80 to 85 percent.
Diagnosis The most common sign of CEA is the presence of
an area of undeveloped choroid (appearing as a pale spot) lateral to
the optic disc. The choroid is a collection of blood vessels supplying
the retina. CEA can also cause retinal or scleral coloboma, coloboma
of the optic disc, retinal detachment, or intraocular hemorrhage. It
can be diagnosed by fundoscopy by the age of six or seven weeks.
Severe cases may be blind.
Treatment There is no treatment.
Breeding and Testing Controversies exist around eliminating this
disorder from breeding Collies. Some veterinarians advocate only
breeding dogs with no evidence of disease, but this would eliminate a
large portion of potential breeding stock. Because of this, others
recommend only breeding mildly affected dogs, but this would never
completely eradicate the condition. Also, mild cases of choroidal
hypoplasia may become pigmented and therefore undiagnosable by the age
of three to seven months. If puppies are not checked for CEA before
this happens, they may be mistaken for normal and bred as such.
Checking for CEA by seven weeks of age can eliminate this possibility.
Diagnosis is also difficult in dogs with coats of dilute color because
lack of pigment in the choroid of these animals can be confused with
choroidal hypoplasia. Also, because of the lack of choroidal pigment,
mild choroidal hypoplasia is difficult to see, and therefore cases of
CEA may be missed.
Until recently, the only way to know if a dog was a carrier was for it
to produce an affected puppy. However, a genetic test for CEA became
available at the beginning of 2005, developed by the Baker Institute
for Animal Health, Cornell University, and administered through
OptiGen. The test can determine whether a dog is affected, a carrier,
or clear, and is therefore a useful tool in determining a particular
dog's suitability for breeding.