Collie Eye Anomaly: Causes, Symptoms & Treatment
The Collie family of dog breeds is fascinating. Dogs that are a part of the Collie breeds are intelligent, playful, and energetic. They don’t just make some of the best herding dogs in the world, but they also make fantastic family pets. They are a complete joy to train, and their owners will absolutely enjoy watching their dogs develop. However, these dog breeds are prone to a specific eye problem called the collie eye anomaly or collie eye defect. If you have a Collie at home, here’s what you should know about the collie eye anomaly.
Collie eye anomaly, also known as collie eye defect, is a congenital (inherited) condition. The chromosomes that govern eye development are mutated, resulting in an underdeveloped choroid (the collection of blood vessels that absorb scattered light and nourish the retina). The mutation can also cause other eye defects with more severe consequences, such as retinal detachment. When this mutation occurs, it always affects both eyes, though it may be more severe in one than the other.
A chromosome 37 defect is the cause of the collie eye anomaly. It only happens in animals with a parent or parents who have the genetic mutation. Although the parents may not be affected by the mutation and thus have not been diagnosed with the abnormality, offspring can be affected, especially if both parents carry the mutation. It is also suspected that other genes are involved, which would explain why the disorder is severe in some collies and so mild in others.
Rough and Smooth Collies in the United States and Great Britain are affected to varying degrees, as well as Rough Collies in Sweden. Border Collies are also affected, though to a much lesser extent (two to three percent). It has also been observed in Australian Shepherds, Shetland Sheepdogs, Lancashire Heelers, and other herding dogs.
While a veterinarian can determine whether your dog has this defect through genetic testing, there may be no symptoms until the onset of blindness alerts you to the problem. There are various stages of this disease, some more visible than others, that lead up to the final result. Some associated conditions that may occur with this defect include;
- Microphthalmia - the eyeballs are noticeably smaller than normal
- Enophthalmia - the eyeballs are abnormally sunken in their sockets
- Anterior corneal stromal mineralization - the connective tissue of the cornea (the transparent coat at the front of the eye) has mineralized, resulting in a cloud over the eyes
- Retinal folds - the retina's two layers do not form properly.
Many dog breeders screen for this condition, with veterinary ophthalmologists performing examinations on puppies that are between 6 and 8 weeks old. Unfortunately, CEA is not always detected until the dog's vision is impaired. Your veterinarian can diagnose CEA by examining the retina, which is located at the back of the eye with the pupil dilated.
Your veterinarian may also advise you to see a veterinary ophthalmologist for a thorough eye examination. Some of the eye structures may be thinning (choroidal hypoplasia) or have a hole known as a coloboma. A detached retina, which can occur as a complication of a coloboma, may also be associated with CEA.
This condition is irreversible. However, for specific defects, such as coloboma, surgery can sometimes reduce the disorder's effects. Laser surgery is an option your veterinarian may recommend. Another option for preventing retinal detachment or further deterioration is cryosurgery, which uses extreme cold to destroy unwanted cells or tissue. In some cases, surgery may aid in the reattachment of the retina.
If your dog has a coloboma, they should be closely monitored for signs of retinal detachment during the first year of life. After a year, retinal detachments are uncommon in all breeds prone to collie eye anomaly.
In terms of prevention, there is no way to avoid the condition once the dog pregnancy has occurred. The only way to get rid of the trait is to avoid breeding dogs with this specific chromosomal defect. Simultaneously, breeding minimally affected dogs to other minimally affected or carrier dogs may produce minimally affected offspring. Such breedings, however, can produce any level of severity. Breeding more severely affected dogs will almost certainly result in severely affected offspring.
Over eight years, one study examined 8,204 Rough Collies in Sweden (76 percent of all Collies registered in Sweden) and discovered that breeders tended to select against dogs with colobomas but continued to breed dogs with the defective chromosome. From 1989 to 1997, the strategy resulted in a significant increase in the occurrence of the defective chromosome, from 54 to 68 percent, and an increase in the prevalence of colobomas, from 8.3 percent to 8.5 percent. Another effect was that when at least one of the parents had a coloboma, the litter size was significantly reduced.
World Dog Finder team