UNDERSTANDING COLLIE EYE ANOMALY
Kathy Moll – Deep River Collies
Collie Eye Anomaly (CEA) is a congenital, inherited condition of several breeds (most especially the collie). Collie puppies should be checked for CEA by a Veterinary Ophthalmologist before they are placed in new homes.
CEA affects 85% to 90% of collies. Of the 10% to 15% of the unaffected collie population, fewer than 50% are normal eyed/non-carriers. Most CEA has not proven to be vision impairing in clinical studies, so owners will rarely see any discernable difference between collies with CEA and those who are not affected (normal eyed collies). Exceptions are explained below.
Collies with the least serious form of CEA have what is called choroidal hypoplasia, chorioretinal dysplasia, or chorioretinal change. These three terms are used interchangeably and describe the same condition – a pale, thin area in the choroid – both eyes. Collies with this mildest form of collie eye retain normal vision throughout life. This form is present in about 75% of collies with CEA. The reason for checking litters by 8 weeks of age is that some collie puppies have such a small pale area that they can appear to be normal eyed shortly after 8 weeks. These are typically described by breeders as “go-normals.” Even with sophisticated ophthalmologic equipment, these collies will appear as normal (no collie eye) just as true normal collies.
Coloboma and staphyloma are more serious forms of CEA. These may occur in only one eye or in both eyes. Colobomas are seen at or near the optic nerve as a cleft or out pouching. Staphylomas appear as an area of thinning in the sclera, adjacent to the choroid. Small to moderate clefts rarely change and do not seem to affect the collie’s visual acuity. Therefore, most collies with this problem make suitable companions and have no problems throughout life. Around 15% to 20% of collies have this form of CEA, usually in one eye but occasionally in both eyes. In rare cases a large coloboma may be present which presents the risk of causing a serious problem – a tear in the optic nerve/disc. Vision impairment and eventual blindness may occur in an eye with a large coloboma.
Fewer than 10% of collies affected with CEA have the most serious form of the disease – retinal detachment. This blindness-causing defect (partial or total) usually occurs in one eye but may occur in both. Puppy eye checks reveal this serious defect. Collies who are detached in one eye can lead relatively normal lives.
Genetically, CEA as a syndrome is a simple recessive trait; however, its degree of expression is more complex. At present the modifiers that control the expression of CEA are not known. The good news is that they may be identified with further study now that CEA has been located to chromosome 37.
Statistics included above are based on best available veterinary information. For more extensive genetic information on CEA click here: http://www.optigen.com/opt9_test_cea_ch.html