Collie Eye Anomaly
Collie Eye Anomaly, or CEA, is a genetic disorder of the eye found in multiple breeds, including most frequently in herding dogs, especially collies and Shetland sheepdogs. The mutation affects the inner structures of the eye, such as the choroid, the retina and the optic disk.
Researchers first noted this problem in the 1960s, but the mutation was only pinpointed in 2007. It was found to exist in most Collies and in most Collie families. CEA’s physical symptoms are present prior to birth. It can present, however, with different degrees of severity.
Collie Eye Anomaly (CEA) can be easily checked when the puppies are 6-8 weeks old, by a Board Certified Ophthalmologist. The eyes are dilated prior to the examination, so the interior of the eye can be examined with an ophthalmoscope. If the puppy’s eyes are not normal, the actual abnormality is noted. Historically, a grading system (mild/moderate/severe) was used, but today only the abnormal findings are noted. Most dogs with CEA today have no vision defects, thanks to multiple generations of breeding only the least severely affected dogs.
CEA is an autosomal recessive disorder, which means a dog requires two copies of the mutation to show symptoms. Thankfully, this disorder generally does not worsen over time.
Ophthalmic examination for CEA should be done by all breeders on their puppies at 6-8 weeks. The genetic mutation for CEA can also be tested for using the Optimal Selection test, however this will not replace examination by an ophthalmologist...
Click here for more information on the Optimal Selection test!
The Collie Health Foundation is currently funding research and sponsoring a sample request to identify the genetic markers for the more severe forms of CEA. Follow this link for more information on how you can participate in this research! All sample handling and shipping costs are reimbursed by CHF, regardless of membership, upon receipt of the sample(s).
FAQ
- Can my Collie’s eyes become worse? Might he later go blind?
A dog born with a severe Staphyloma or with Vascular Disease may later suffer loss of vision if a detachment or severe hemorrhage occurs. The majority of dogs that are mildly affected will generally have perfectly adequate vision throughout their life. Even a dog with one blind eye will adapt perfectly well in his surroundings.
- What have breeders done to improve Collie eyes?
When the eye problem was identified more than 50 years ago, it was estimated that 90% of the Collie population was affected with some form of eye disease. Because CEA has involved such a large percentage of the breed, eradication is difficult. Over the years, with selective breeding and ophthalmic examination of breeding stock, the number of seriously affected Collies has been greatly reduced. ALL reputable breeders should have not only their breeding stock, but all puppies that are offered for sale examined by a board certified ophthalmologist.
The Collie Club of America’s Code of Ethics also requires …
“3. All dogs shall be transferred, sold or placed in good condition, free of communicable diseases with health guaranteed for a reasonable length of time. This should include a written health record, including an inoculation schedule and an eye examination done either by a licensed veterinarian trained in veterinary ophthalmology or a certified ophthalmologist. . It is also suggested that the dogs have some type of permanent identification, such as a microchip or tattoo.”
Watch the CHF Breeder’s Education Seminar on Genetic Collie Eye Diseases
presented in 2020 by Susan Pearce-Kelling of Wisdom Health
CEA Eye Grades and their Meaning
Normal: A “Normal” eye rating is, of course, ideal. However, some normal-eyed collies still are affected by the mutation and breed as affected. The only way to determine if a Collie is genetically normal is a DNA test. There are variations even in “Normal” eyes that correspond somewhat to a dog’s coat color. It is often difficult to judge choroidal hypoplasia in a Blue Merle’s eyes as the retinal pigment is diluted along with his coat color, and can sometimes be diagnosed as Choroidal Hypoplasia.
Choroidal Hypoplasia is an abnormality in the development or pigmentation of the choroid. The choroid is a vascular bed beneath the retina. This is the most common abnormality found in Collie eyes. It is the least harmful and least severe form of CEA. Most dogs with this eye grade function normally with no obvious vision deficits. Puppies with minimal choroidal hypoplasia may look normal at subsequent examinations because the area fills in with pigment. These puppies used to be referred to as “go normal”, but since they remain affected genetically, the term used now is that the area may be “masked” at a later date. This is the only grade of CEA collie breeders are allowed to use for breeding.
Retinal folds occur when the developing retina folds on itself. It is commonly seen associated with CEA in puppies. These folds commonly resolve with age.
Staphyloma, Coloboma, Ectasia: While not completely synonymous, these terms all refer to a cupping or bulging in the back of the eye, usually in the area of the optic disc. These conditions may or may not be of serious nature. It depends on the size and/or where the “bulge/cupping” is located. Large colobomas or severe ectasia of the sclera can lead to retinal detachment.
Vascular Disease or Tortuous Blood Vessels are defects in the blood vessels of the eye which are responsible for its supply and “nourishment.” These may be malformed, undersized, or even lacking.
Retinal Detachment is a loosening or separation of the inmost, or retina, layer from the wall of the eye. This may involve a tiny area or the entire retina. It can be either one or both eyes. The complete detachment of the retina results in blindness. This is the most severe grade of CEA.
CEA Genetics and their Meaning
Mutant/Mutant – These dogs carry two copies of the mutation and can be affected in different grades of severity. These dogs will always pass an affected gene to their offspring.
Mutant/Normal – These dogs carry one copy of the mutation and will not be affected by CEA. They can produce either normal or affected dogs, depending on the dog they are bred to.
Normal/Normal – These dogs do not carry any copies of the mutation. Their offspring will not show CEA, but may be carriers.
The Science
The mutation for Collie Eye Anomaly was identified in 2007 by Elaine A. Ostrander, Ph.D. at the National Human Genome Research Institute of the NIH. They identified a shared deletion in a section of the gene NHEJ1 that is common to all dogs affected by CEA. This deleted section involves a sequence of DNA that is extremely conserved throughout mammalian genomes, possibly due to it’s importance in proper eye development. A neighboring gene, IHH, could also be the cause of improper eye development due to its known involvement in cell differentiation in developing embryos.
References
Parker, H. G., Kukekova, A. V., Akey, D. T., Goldstein, O., Kirkness, E. F., Baysac, K. C., Mosher, D. S., Aguirre, G. D., Acland, G. M., & Ostrander, E. A. (2007). Breed relationships facilitate fine-mapping studies: a 7.8-kb deletion cosegregates with Collie eye anomaly across multiple dog breeds. Genome research, 17 (11), 1562–1571. https://doi.org/10.1101/gr.6772807
