Collie Eye Anomaly (CEA)
What is Collie Eye Anomaly?
Collie eye anomaly (CEA) is an inherited collection of eye problems that can cause vision defects. Dogs are born with the inherited DNA mutation and the eye abnormalities may develop after birth so it may not be congenital or a birth defect. Some elements of CEA like retinal folds can appear after birth and disappear as the dog ages. Retinal detachments can worsen over time so it can be a progressive disease.
Affected dog breeds include Collies, Australian shepherds, Border collies, Shetland sheepdog, and others.
DNA mutations causing CEA can cause areas of the retina (the nerve layer of the eye with rods and cones) and/or the choroid (the choroid is the blood vessel layer under the retina) to not develop the way it should. The damage to an individual’s vision depends on the severity of the syndrome. Many dogs are carriers for the DNA mutation but do not have the disease, while other dogs are affected and can have various eye problems as a result. It is possible for a retina to detach early or later in life, causing blindness in that eye.
How is CEA inherited?
The disease is inherited in an autosomal recessive so both parents have to carry the DNA mutation and pass it on to their offspring. The dogs with the mutation from one parent will not have disease and are called carriers. If both parents are carriers then 25 percent of the puppies will have the disease with two copies of the mutation, 50 percent will be carriers with one copy of the mutation, and 25 percent will be clear with no mutations. If a carrier is mated to a normal dog then 50 percent of the offspring will be clear, and 50 percent will be carriers. Dogs with CEA or carriers of the CEA mutation should not be bred to each other.
Breeders of dog breeds that can have CEA should have their dogs screened for CEA before breeding individual dogs with CAER exams performed by a veterinary ophthalmologist. The genetic test for CEA can determine if that dog is normal, a carrier and has CEA with 90-95% accuracy. Even puppies can have genetic tests as long as they are large enough for your veterinarian to safely take a teaspoon of blood to send in for testing.
Puppies can be checked by a veterinary ophthalmologist at 5-6 weeks old, and preferably before 12 weeks of age. Their pupils must be dilated for this examination. Responsible breeders should conduct the genetic testing on the parents and have puppies' eye examined before 12 weeks of age to determine which dogs should or should not be bred.
Dogs that appear normal may still be carriers for the CEA mutation. Breeding two carrier dogs to each other can produce 25% puppies with CEA and 50% mutation carrier puppies. Even parent dogs with no signs of the CEA disease can produce severely affected puppies with blindness or ongoing eye problems. Nonetheless, selective breeding is helping to reduce the number of cases around the world.
What are the signs of CEA?
The choroid, the blood vessel layer underneath the retina, may not develop causing choroidal hypoplasia. This is the most common problem found in CEA. When the blood vessels do not develop under the retina (layer with rods and cones), the retina cannot be viable or functional without a nutrient supply. The areas of choroidal hypoplasia cause blind spots in vision.
Retinal folds occur when the retina is too large for the eye and creates folds inside the eye. Retinal folds can disappear with age so they may not be seen in the CAER eye exam of a dog over 12 weeks of age. A CAER eye exam just before 12 weeks of age is ideal. CEA eye problems require extensive training in veterinary ophthalmology and specialized eye exam equipment to be seen.
A separation between the retina and choroid called a retinal detachment can be a part of CEA. The retinal detachment may involve part or all of the retina. Complete retinal detachment cause blindness in the affected eye. Retinal detachment can be seen at any age or may develop later in life. If a retinal detachment occurs, the retina separates from the choroid or blood vessel layer that supplies the nutrients so blindness will occur at that location.
A coloboma is a focal defect in the eyeball where a focal area cups outwards, often near the optic disc. Severe cases can be associated with blindness or retinal detachments.
How is CEA diagnosed?
Typically, CEA is diagnosed during a CAER eye exam by a veterinary ophthalmologist who looks at the front of the eye and the fundus (back of the eye) when the dog’s pupil’s are dilated. CEA can also be diagnosed with a DNA test.
Diagnosis of this disease is very important in breeding animals because it is hereditary and can be passed on to future generations!
How is CEA treated?
There is no cure for CEA although some of the eye problems have treatment options like surgery for progressive retinal detachments if they worsen over time. Generally speaking, most dogs with CEA have abnormal vision and their vision is affected by choroidal hypoplasia and colobomas (see above) in addition to the retinal detachments.
Dogs with CEA should see veterinary ophthalmologists for medical care and to try to avoid painful complications of CEA.