Collie Eye Anomaly (CEA)
Collie eye anomaly (CEA), also known as choroidal hypoplasia (CH), is an inherited disease affecting several dog breeds. The choroid is the layer of tissue in the eye responsible for supplying blood and nutrients to the Retina. In dogs affected with CEA, the choroid does not develop properly and is therefore thinner than normal. The severity of the condition can vary from dog to dog. In mild cases, affected dogs may only show signs of collie eye anomaly on eye exam between about 5 and 12 weeks of age, just prior to normal age-related pigmentation of the retina which often masks the characteristic, disease-related changes. After this time period, mildly affected dogs may be impossible to distinguish from normal dogs on eye exam (a phenomenon often referred to as “going normal”) and may not display obvious vision deficits.
In more severely affected dogs, clinical signs include malformations of the eye and/or optic nerve (colobomas), retinal detachment, and possible blindness. Both mild and severe forms of CEA are associated with the same gene Mutation. Therefore, predicting the potential severity of the disease in an affected puppy is difficult as affected parents may produce offspring that are severely affected.
The CEA/CH genetic test provides the life-long genetic status of a dog for this disease. In conjunction with genetic testing, an eye exam (CERF) by a veterinary ophthalmologist is recommended before 8 weeks of age.
The eye exam will give you information about mild versus severe CEA/CH disease among affected dogs.
Normal Non Carrier (NC) (+/+)- the dog is free of CEA and will not pass an affected CEA Gene to their get.
Normal Carrier (NE) (+/-)- the dog is free of CEA but has 1 normal gene and 1 CEA gene.
Affected (Mild, Moderate, Go Normal)(-/-) - The dog has CEA, but not a severe case, this dog will not have any vision issues due to CEA. When bred this dog cannot pass on a true normal gene when bred to another affected dog.
Affected severely (-/-) -(colobomas, optic nerve colobomas, retinal detachment)- This dog has CEA and can possible lead to blindness. These dogs should not be used in a breeding program, and any puppy buys must be notifiead of the severity of the issue in the puppy. Some dogs with Colobomas can live a full life without any noticable changes in vision.
Explanations of the sever CEA related issues:
Coloboma is a defect of the sclera, such that a hole appears in the optic disc, or next to it. A hole in the disc itself is called a Papillary Coloboma and a hole next to the optic disc is called a Peripapillary Coloboma. A thin area or very small hole next to the optic disc will not impair vision, but obviously the larger the coloboma the more distorted vision will be and a very large coloboma will almost certainly result in a partial detachment of the retina.
Optic Nerve Coloboma located at the back of the eyes where they establish a direct connection to the brain, are responsible for vision. Should embryologic development not proceed normally, however, bits of the optic nerve may be left out of the process. This creates a “pitted” or “cratered” area within or adjacent to the optic disc (where the optic nerve attaches to the eye). We call this lesion an optic nerve coloboma. If the defect is large enough, normal nerve conduction related to vision can be disrupted and vision impairment ensues.
Retinal Detachment is where the retina becomes detached from the underlying tissue, at some point or points, resulting in the retina becoming loose, possibly showing signs of multiple folding or rippling. Vision will be affected and blindness will occur with a complete detachment. Having stated earlier that the disease is not progressive, it should be said that it may appear to be so, when a partial detachment becomes complete, causing total blindness in an already poorly sighted eye.
Expected Results of Breeding Strategies for inherited Recessive Diseases
Normal NC x Normal NC All Normal NC
Normal NC X Normal Carrier 50% Normal NC, 50% Normal Carrier
Normal NC x Affected All Normal Carrier
Normal Carrier x Normal Carrier 50% Normal Carriers, 25% Normal NC, 25% Affected
Normal Carrier x Affected 50% Carriers, 50% Affected
Affected x Affected All Affected