Collie Eye Anomaly in Dogs
Collie eye anomaly, also referred to as collie eye defect, is an inherited congenital condition. The chromosomes that determine the development of the eyes are mutated, so that the choroid (the collection of blood vessels that absorb scattered light and nourish the retina) is underdeveloped. The mutation can also result in other defects in the eye with more severe consequences, such as retinal detachment. When this mutation does occur, it is always in both eyes, although it might be more severe in one eye than the other. Approximately 70 to 97 percent of rough and smooth collies in the United States and Great Britain are affected, and approximately 68 percent of rough collies in Sweden are affected. Border Collies are also affected, but at a much lower two to three percent. It is also seen in Australian Shepherds, Shetland Sheepdogs, Lancashire Heelers, and other herding dogs.
Symptoms and Types
While a veterinarian can determine through genetic analysis whether your dog has this defect, there may be no symptoms, until the onset of blindness signals you to the problem. There are stages of this disease, some more obvious that others, that lead up to the final outcome. Some associated conditions that may occur with this defect are microphthalmia, where the eyeballs are noticeably smaller than normal; enophthalmia, where the eyeballs are abnormally sunken in their sockets; anterior corneal stromal mineralization -- that is, the connective tissue of the cornea (the transparent coat at the front of the eye) has become mineralized, and shows as a cloud over the eyes; and an effect that is less obvious on inspection, retinal folds, where two layers of the retina do not form together properly.
The cause of collie eye anomaly is a defect in chromosome 37. It only occurs in animals that have a parent, or parents, that carry the genetic mutation. The parents may not be affected by the mutation, and may therefore not have been diagnosed with the abnormality, but offspring can be affected, especially when both parents carry the mutation. It is also suspected that other genes may be involved, which would explain why the disorder is severe in some collies and so mild that it causes no symptoms in another.
Your veterinarian will conduct a thorough examination of the eyes to determine the extent of the defect. This can be done when your dog is still a puppy, ans is recommended. Retinal detachment is most common in the first year, and can be prevented or minimized if it is caught early on. Consult with your veterinarian about your dog’s vision. If the disease is diagnosed, it will not be expected to worsen initially unless there is a coloboma -- a hole in the lens, choroid, retina, iris, or optic disc. A coloboma may be small and have very little effect on vision, or it can be a larger hole that takes away too much of the eye structure and leads to partial or full blindness, or to retinal detachment. A coloboma, if found, will need to be carefully monitored by your veterinarian. Some patients with a minor defect may develop pigment across the affected area but will appear normal. For this reason, early examination of your collie (or herd dog) in the first six to eight weeks of life is highly recommended.