Collie Eye Anomaly

Collie Eye Anomaly by Jennie Bullock

Collie eye anomaly (CEA) has long been a problem in collies, although it is not exclusive to collies. Once it was identified, most breeders diligently went to work on decreasing this problem. Through screening and responsible breeding there has been some success in decreasing the severity of the problem although there has been minimal success in decreasing the number of collies with the problem.
Collie Eye Anomaly is an inherited disease characterized by abnormal development of the eye. Mild cases are characterized by lack of development of the choroid, which is the vascular layer of the back of the eye (choroidal hypoplasia) , and vascular tortuosity. In more severe cases, the dog may have patchy areas where the choroid is missing and bare sclera is visible. Colobomas are outpouches of the sclera, and may be found in the most serious presentation of CEA. The colobomas may be small or large and may affect the optic disc or be adjacent to the optic disc. Dogs with colobomas have a higher incidence of development of a retinal detachment, or retinal hemorrhage, or both which can result in blindness.
Recessive genes in the gene pool of popular dog breeds, can become embedded very quickly. In Collies, the recessive gene for Collie Eye Anomaly is now so established in the breed in the US that most examining opthalmologists agree the number of AFFECTED (carrying two genes!) animals is around 85%. Of the 15% that are "normal" (a dominant gene), many of these are carriers.
Consequently, we still have a very high percentage of collies affected, but most have very little vision impairment. They have small blind spots due to the lack of cones that receive light images. Usually both eyes are not focusing on a blind spot at the same time, so the dog can always see. This problem doesn't get worse with age. However, if a pup has a coloboma, that could get worse with age. If that coloboma is near the optic nerve, that pup will probably go blind someday. However, since CEA does not cause significant vision impairment in the majority of animals, many collie breeders tend to believe it is alright to produce these affected animals as long as the puppies are eye tested and the small percent with probable vision impairment are not sold.
This condition can be detected by examination of the retina of the eye as early as 5 to 8 weeks of age. Be aware though, that there is also a possibility that some puppies to appear to "go normal", usually around 8-12 weeks, but this is a false normal and genetically still 100% affected. If eye checks aren't done on all litters, the severity could get worse again. Pups must be checked prior to eight weeks of age. After that age, a very mildly affected pup could test normal because what the doctor is looking for can be covered over with pigment making it impossible to see. Most Collie breeder have pups checked before selling them, by a veterinarian specialized in ophthalmology.
A number of dog breeders who have worked with this for years believe there are also modifiers inherited which affect the expression of the anomaly causing more/less expression or degree of the problem. If you are buying a pup with a normal eye check and the breeder tells you that both parents are affected, don't believe it. It's not possible to get normal eyes from two affected parents. Either the eye check was wrong, or the sire of record is false. CEA is a recessive gene, taking two affected genes to make an affected eye. One affected gene makes a normal eye, but a carrier. Since there are only two genes involved (one from each parent), and both parents are affected (two affected genes each), the pup must be affected.
Because CEA has involved so much of the breed, eradication has had to be slow in order to keep other desirable qualities. Even among the dogs that examine clear, most are carriers of the gene. The Collie Club of America encourages its members to have all their puppies checked as young as possible by a veterinary ophthalmologist. No dog should be used for breeding until examined and found to be above the examiner's standard. Because most affected collies can perform all normal duties/functions and are acceptable to the buying public, there has been no real push to remove this syndrome from the breed.
Often, breeders and veterinarians mistakenly believe this is a problem only in the United States. However, many of the collies in the British Isles and elsewhere are examined well past the age to catch the "go normals" and these dogs are certified falsely as "normal" while genetically affected. Dr. Rubin in Inherited Eye Diseases in Purebred Dogs lists the number of CEA affected collies for the US (depending on region), 50% to 90%, the latter being more usual; United Kingdom, 64%; Germany, 37%; Netherlands, 41%; and Switzerland, 31%.
The above information is not meant to indicate the Collie breeders are uncaring about genetic problems; only that they consider CEA to be one of the least troubling and with the least consequences. Collie breeders are presently funding not only the search for a DNA marker for PRA, but also for DM (dermatomyositis), a muscle wasting disease that expresses itself also as a skin disorder, and a number of other genetic problems identified within the breed. However, the huge numbers of Collies affected and thus pure for a RECESSIVE disorder (CEA) is meant to show how quickly and silently some of these things can develop within a breed.

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