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CEA Explaintion
Carrier of CEA
A note to people wanting a pet & companion puppy only ...95% of collies have some form of CEA. Even if they are normal eyed they can be a carrier of CEA. A mildly effected puppy is NOT a bad thing. Humans have eye problems and we have no problem with that, so please do your homework, ask questions and keep an open mind. Only the true normal eye collie is a NON Carrier of CEA. And this eye exam can only be given by a Certified Canine Ophthalmologist. NOT A VET!
CEA is thought to be inherited via a simple autosomal recessive gene. There is currently some speculation about how CEA is inherited as no test has ever been run to determine how it is inherited.
Terms used when talking about CEA are:
Affected: An affected dog is one who, upon dilation of the eye, shows a visible deviation from a normal or unaffected eye when viewed with the proper instruments. To be affected a dog must have inherited an affected gene from both parents.
Vessel Tortuosity: Although originally thought to be a form of CEA, vessel tortuosity is a separate condition which may appear in conjunction with CEA. Vessel tortuosity appears in many breeds other than Collies and those affected by CEA. This condition has been traditionally referred to as a grade 1 in most eye check grading systems.
Choroidal Hypoplasia (AKA Chorioretinal Change, Choroidal Dysplasia or Choroidal Hypopigmentation: this is visible as pale areas on the fundus or as areas where the cells of the tapetum are abnormally developed or missing; fewer blood vessels exist in the choriod and pigmentation is diminished. This condition does not affect the dog's ability to see. This condition has been traditionally referred to as a grade 2 in most eye check grading systems.
Coloboma, Staphyloma or Ectasia: The coloboma is a problem that begins during embryonic development, in which the choroidal fissure, an opening in the eye tissue through which blood vessels grow, fails to close, causing the area in or around the optic nerve to remain underdeveloped. Colobomas usually appear as a hole or indentation near the optic nerve. Viewed with a microscope, it can be observed that the sclera is thin and the tapetum, choroid, and retina may be abnormally formed or entirely absent. Staphylomas are similar to colobomas but occur elsewhere on the fundus. These can be visualized as soft spots in an inflated balloon. Colobomas and staphylomas create blank spots in the dogs vision, spots where they cannot see as well. These conditions can occur in conjunction with choridal hypoplasia.
Choridal Hypoplasia and Staphyloma are not progressive. What the dog displays at 6 weeks is what he/she will have for life. Colobomas can lead to retinal detachment. Staphyloma's have traditionaly refered to as a grade 3 in most eye check grading systems and Coloboma's have been referred to as grade 4's.
Retinal Detachment: a dog with a detached retina will be blind in that eye. This condition has been traditionally referred to as a grade 5 in most eye check grading systems.
Normal eyed: A normal eyed dog is a dog who, when examined by a veterinary ophthalmologist displays no visible signs of CEA, but possesses only one normal gene; the other gene is affected.
Non-carrier: A non-carrier is a normal eyed collie who possesses, or carries no affected genes. He therefore cannot produce anything but normal eyed collies.
What You Can Expect from Breeding An ...
Affected to Affected: All affected pups. Both parents have only affected genes and can therefore only pass on affected genes.
Affected to Normal Eyed: should produce 50% normal eyed carriers and 50% affected. Only one gene is required to be normal eyed, the normal eyed parent should produce the normal eyed gene 50% of the time.
Normal Eyed to Normal Eyed: should produce normal eyed non-carriers, normal eyed carriers and affected dogs. It is interesting to note that breeders have found that the percentage of affected dogs, which should be equal to that of non-carriers, out weighs that of non-carriers and of normal eyed dogs. Very few non-carriers have ever come from normal to normal breeding's. Normal eyed dogs which have a non-carrier in their immediate background appear to produce a greater percentage of non-carriers.
Non-Carrier to Normal Eyed: Should produce 50% normal eyes and 50% normal eyed non-carriers. Again it only requires one affected gene to be a carrier, and the normal eyed parent should produce the normal eyed gene 50% of the time. Unfortunately there has not been enough non-carrier to normal eyed breeding's to establish whether or not this is how it is actually working.
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Non-Carrier to Non-Carrier: can only produce non-carriers. A dog cannot pass on a gene it doesn't have.
Much confusion has historically been present, and is still present in the collie world, due to the lack of uniformity in grading systems. The advent of the CERF form with its diagnostic terms rather than a numerical grading system, is helping to clear up some of the problems with credibility of eye checks.
How Do You Know If A Dog Is A Non-Carrier?
A non-carrier cannot be diagnosed by an eye check, as we are dealing with genes not effects of genes. Obviously if a dog comes from two non-carrier parents, he is a non-carrier. Otherwise whether or not a dog is a non-carrier can only be defined by breeding. If a dog produces a significant number of puppies, bred to an affected or normal eyed stud or bitch, and all have normal eyes, no matter what the eye check of the other parent is, it's a safe bet he/she is a non-carrier.
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