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What is collie eye anomaly (CEA)?
CEA is a disorder of the deep structures of the eye that affects collie breeds around the world.
The four main changes are:
Inadequate development of the choroid, a thin layer of blood vessels that delivers oxygen and
nutrients to the retina (called hypoplasia of the choroid or chorioretinal dysplasia);
Coloboma - a cleft or defect of the optic disc or adjacent areas;
Staphyloma - an area of thinning in the sclera which is adjacent to the choroid; and
Retinal detachment with or without haemorrhage - a complication associated with the
other defects
CEA is a disorder of the deep structures of the eye that affects collie breeds around the world.
The four main changes are:
Inadequate development of the choroid, a thin layer of blood vessels that delivers oxygen and
nutrients to the retina (called hypoplasia of the choroid or chorioretinal dysplasia);
Coloboma - a cleft or defect of the optic disc or adjacent areas;
Staphyloma - an area of thinning in the sclera which is adjacent to the choroid; and
Retinal detachment with or without haemorrhage - a complication associated with the
other defects
| In its mildest form, there are minor changes in the choroid which will have little effect on sight. About 25 per cent of dogs with CEA have colobomas/staphylomas as well as choroidal hypoplasia. Retinal detachments occur in approximately seven per cent of dogs with CEA. Total retinal detachment will cause blindness. |
Possible genes (one gene from each parent for a total of 2 genes per dog) a - affected gene (recessive gene) N - Normal-eyed gene (dominant gene) |
| Possible combinations (per dog) NN-----> Normal eyed non-carrier Na ------> Normal eyed carrier aa -------> affected dog |
Dam
a
a
| The sire is affected. The dam is affected. Offspring: All affected. |
|
a
Sire
a
Dam
a
a
| The sire is a normal-eyed carrier. The dam is affected. Offspring: 1/2 are normal-eyed carriers. 1/2 are affected. |
|
N
Sire
a
Dam
a
a
| The sire is a normal-eyed non-carrier. The dam is affected. Offspring: All normal-eyed carriers |
|
N
Sire
N
Dam
a
N
| The sire is a normal-eyed non-carrier. The dam is normal-eyed carrier. Offspring: 1/2 normal-eyed carriers. 1/2 normal-eyed non-carriers. |
|
N
Sire
N
Dam
a
N
| The sire is a normal-eyed carrier. The dam is normal-eyed carrier. Offspring: 1/2 normal-eyed carriers. 1/4 normal-eyed non-carriers. 1/4 are affected. |
|
N
Sire
a
Dam
N
N
|
| The sire is a normal-eyed non-carrier. The dam is normal-eyed non-carrier. Offspring: All normal-eyed non-carriers. |
N
Sire
N
| Collie Eye Anomaly (Choroidal hypoplasia) |
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| Collie eye anomaly was first reported in 1953. The original report included a description of a pale area in the retinal along with staphylomas and retinal detachments. CEA is the incomplete development of the eye which is present as early as the 28th day of gestation. The defect involves the sclera, the choroid, the retina, the retinal vasculature, and the optic disc. Clinically, the severity of the anomaly is variable ranging from no apparent visual defect to total blindness. It is found in rough and smooth Collies and all color coats are involved. Most Collies (80 to 90%) with CEA do not demonstrate vision problems. CEA is a simple recessive defect and therefore is expressed in the homozygous state only. Carriers and normals can not be distinguished based on an ophthalmic examination. A number of researchers have attempted to separate the various aspects of the disease, i.e. the choroidal hypoplasia from the ectasia (pits) but were unable to do so. When the disease was first described such a large percentage of the population was affected that a number of simple grading systems were devised to make classifications of individuals easier. In addition, it was the feeling of some people at that time that the severity of the disease might be ameliorated by breeding less afflicted individuals. Certainly this concept has had its place in history of breeding better Collies. Unfortunately, dogs with minor afflictions can and do produce severely afflicted offspring's. Likewise, blind parents can produce less afflicted offspring. For the purpose of genetic selection, an individual with the mildest affliction is just as bad as a totally blind dog. Because the grading system remains firmly entrenched within the Collie fancy a discussion of the grades and categories is appropriate. Grade 1 - torturous retinal vessels, extremely small areas of choroidal hypoplasia Grade 2 - torturous retinal vessels, substantial areas of choroidal hypoplasia Grade 3 - torturous retinal vessels, substantial areas of choroidal hypoplasia with colobomas (pits) or areas of ectasia in the posterior segment. Grade 4 - all of the above defects with a retinal detachment Grade 5 - all of the above defects with a retinal hemorrhage It is possible for one eye to have a different grade than the other, but if one eye is affected then both eyes in almost all cases are affected. "Go normal" is a term used to describe an affected individual, Grade 1 or Grade 2, in which the area of choroidal hypoplasia fills in so it appears normal at later examinations. These animals act genetically like the affected individuals that they are. They can set a breeding program back years, however. Because the lesion is present in the neonatal puppy, eyes can be checked as early as 5 to 6 weeks of age. For the ease of the examiner and to facilitate a more accurate exam, evaluation at 6 to 8 weeks of age is recommended. |
