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It has been estimated that human eyes can distinguish roughly 10 million different colors. Human eyes have three types of cones that can identify combinations of red, blue, and green. Dogs, on the other end, possess only two types of cones and can only discern blue and yellow – this limited color perception is called dichromatic vision. Which is yet good enough as they can see a lot of pretty colors. But these tiny beautiful eyes of dogs are prone to many diseases. Some of the common eye problems in dogs include –
So, it’s always a good idea to take a close look at your dog’s eyes regularly to see if there are any changes like redness, cloudiness, or tearing.
But there can be some inherited diseases as well which we can’t help prevent. These include cataracts, glaucoma, and retinal degeneration. These disorders affect the dog’s vision and may lead to severe conditions like complete blindness.
Collie eye anomaly is a birth defect, also known as a congenital defect. It is bilateral disease that affects the retina, choroid, and sclera. It is caused by an autosomal recessive gene defect. In genetics, dominance is the phenomenon of one variant. The second one is recessive. The terms autosomal dominant or autosomal recessive are used to describe gene variants on non-sex chromosomes.
CEA is caused by the improper development of the eye. What happens is the cells of the posterior portion of the optic vesicles fail to express growth hormones. This affects the differentiation of other cells of the eye. The degree of these abnormalities varies between individual dogs, and even between the same dog’s eyes. This disease has a proportion of individuals carrying the variant as high as 100%. This is why severe cases can lead to blindness.
The most common symptom or sign of CEA in dogs is blindness. The amount of vision that the dog has will depend on the severity of the developmental defects. There is a possibility that some dogs may have normal vision but eventually even in these dogs, vision loss or blindness can occur, especially if the dog’s retinas are detached.
There are other conditions that are linked to CEA. These include Microphthalmia and Enophthalmia. The former is when the eyeballs appear smaller than normal and the latter is when eyeballs are sunken deep into the eye sockets. Some patients with a minor defect may also develop pigment across the affected area but will appear normal.
The cause of collie eye anomaly is a defect in chromosome 37. It is strictly an inherited condition that occurs when animals have a parent, or parents, carry the genetic mutation. There is a possibility that the parent may not have the disease but just be carrying the mutation. In this case, the offspring can be very well affected. Especially when both parents contain 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 others.
A thorough examination of the eyes to determine the extent of the defect would be conducted by your vet. It is recommended that it be done when the dog is still in his/her young age. In the first year of the puppy with this defect, retinal detachment is a common symptom. This can be contained if diagnosed at an early age itself. Initially, the effects of the disease won’t be major unless there is a hole in the lens, choroid, retina, iris, or optic disc. This is called a ‘coloboma’ which 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.
It can occur in any breed of dog, where the parents are carrying the gene mutation. But statistics-wise, it has been found that there are some breeds that are more prone to the disease than others. These include –
The frequency has been found higher in Collies and Shetland Sheepdogs but low in Border Collies.
Unfortunately, there is no cure or prevention found for this disease as it is purely a genetic one. In the case of coloboma-induced partial retinal detachment, laser surgery may be attempted to re-attach the retina if the condition is detected early. The good thing is that coloboma won’t always lead to a retinal detachment. If the dog has survived without a retinal
detachment in the first year of the disease detection, then there are high chances it won’t happen in the lifetime.
The only way to stop this disease is to stop preventing the breeding of dogs with the mutation. There are now several genetic tests for CEA. It is better to consult your vet before breeding your dog to check if there are some tests necessary.
CEA is an inherited disease found majorly in Collies. There is no prevention or cure as such. But as a responsible and loving parent, you can take measures to conduct a test in the early ages of the dog itself. Early examination of your collie (or herd dog) in the first six to eight weeks of life is highly recommended. Also read about Autoimmune Thyroiditis in Dogs & Epilepsy In Dogs
Happy Mood and Health to your Dog and lots of Love and Licks to you!
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