What is Collie eye anomaly?
Collie Eye Anomaly is an inherited condition affecting both eyes of many different Collie type breeds of dogs. Interesting to note, that not only Collie breeds are affected but also some other breeds. Affected breeds include Rough and Smooth Collies, the Shetland Sheepdog, the Australian Shepherd, the Border Collie, the Lancashire Heeler, and the Nova Scotia Duck Tolling Retriever.
The region of the eye affected by this genetic condition is called the choroid. The choroid is the layers of blood vessels and pigment between the sensory membrane that lines the inner surface of the back of the eyeball (the retina) and the outer white covering of the eye (the sclera). The locations of all the parts being described can be seen in the image below.
The primary lesion is typically the underdevelopment of the choroid called hypoplasia, which results in the appearance of a pale spot on the back surface of the eye when looking through the pupil. More severe consequences may occur such as retinal detachment or bleeding in the eye, both of which may lead to blindness. The back part of the eye where the main nerve that runs from the brain the eye comes into the eye is called the optic disc. With Collie Eye Anomaly one will often find small areas of indentations next to the optic disc. These indentations look like holes in the structure of the eye and are also described as colobomas. The degree to which an individual animal may be affected varies considerably, from very mild, to severe enough that eyesight may be lost completely. The lesions are not progressive and normally do not worsen over time. Mildly affected dogs will just have the pale spot seen on the side of the optic disc. There will be no impact on the dog’s ability to see and the pale spots may be seen in very young puppies and not in adults. The choroidal blood vessels may be reduced in number and abnormal in shape. Up to 25% of dogs that are severely affected will have severe complications that result in significant vision loss. These include the retinal detachment (loosening of the membrane at the back of the eye), bleeding (ocular haemorrhage) and colobomas. This can happen in these severely affected dogs before two years of age and the severity in both eyes may differ. It is very rare for only one eye to be affected by this condition Although this condition does affect vision, it is fairly rare for a dog to be completely blind in both eyes.
How does a dog get Collie Eye Anomaly?
Collie Eye Anomaly is a fairly common condition in affected breeds that has its roots in breeding with affected animals who have not been identified as carriers of the genetic defect responsible. The single most important fact to remember is that Collie Eye Anomaly is genetic and all affected dogs can pass the disorder on to their offspring. It is therefore essential that regardless of the severity of the condition in any individual dog, that they should not be used for breeding. All dogs from affected breeds should be clinically examined and genetically tested before breeding to avoid this unwanted condition to be passed onto their offspring.
How is Collie Eye Anomaly diagnosed?
Diagnosis of this condition is generally confirmed through an ophthalmic (eye) examination by a veterinary eye specialist (veterinary ophthalmologist). The back of the eye is examined through an ophthalmoscope and an area of pallor is identified. This may be done from as early as 5 – 8 weeks of age. As the puppy grows, the retina becomes more pigmented and this may mask the changes in the choroid which means that the eye exam at an older age may appear to be normal, yet the dog still has the condition and is still a carrier of the gene which causes this condition. It is for this reason that all puppies must be examined at a young age, especially if they may be used for breeding later in life. Another fact to understand is that even a mildly affected dog may produce offspring that can be severely affected.
There is also a genetic test available that may be used by vets and breeders to avoid transmission of the disease to the next generation.
How does Collie Eye Anomaly spread?
Having established that Collie Eye Anomaly is a genetic condition where the structure of gene changes (known as a mutation), fortunately, the gene mutation responsible for the defect has been identified. This mutation is found on chromosome 37 on dogs. This is a recessive mutation. A recessive gene is a gene that can be masked by a dominant gene. To have a trait that is expressed by a recessive gene, both parents must pass on the mutated chromosome for the condition to be clinically apparent.
How is Collie Eye Anomaly treated?
Unfortunately, there is no treatment for Collie Eye Anomaly. The best way to prevent this in our dogs is to take part in conscientious responsible breeding, testing all animal from a young age and only breeding with dogs that are negative for both clinical signs and absent genetic mutation. This is our only weapon in the battle against a condition that can be very debilitating to affected pets and it is our responsibility to ensure we aim to breed for the health of our dogs above any other trait that may be deemed desirable.
What is the prognosis if my dog is diagnosed with Collie Eye Anomaly?
The prognosis of Collie Eye Anomaly depends on the extent to which the individual dog is affected. The condition does not normally progress however in early severe cases the indentations (colobomas) around the optic disc where the eye nerve enters the eye from the brain may lead to retinal detachment, which will make the condition severe at an early stage and lead to complete blindness which may lead to euthanasia. If the condition is not so severe and there is partial loss of sight, the dog will learn to cope with the partial loss of sight and will be able to live a good quality life.
It is very important to have any Collie type breed dogs tested for this Collie Eye Anomaly at a very young age (between 6 and 8 weeks of age), so if you do get a puppy that falls in this category of breeds, speak to the vet to set up an appointment with a veterinary eye specialist, to have the test done. A more ideal situation would be to request a certificate from the breeder that you obtain your puppy from, issued by a veterinary ophthalmologist, confirming that the necessary examination and tests have been performed and that the puppy you are obtaining does not have Collie Eye Anomaly.
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