‘Collie Eye Anomaly’ (CEA), also known as ‘collie eye defect,’ is a congenital condition in dogs. Whilst this disease may arise in many dog breeds, it is typically over-represented in collies, hence the name given. This condition presents challenges to those affected including eye defects or visual impairment. This article will explain what CEA is, what the clinical signs are, how it is diagnosed and how we test for it.
What is CEA?
Firstly, CEA is a genetically inherited condition, meaning that affected dogs pass this trait onto their offspring. Don’t worry, I won’t go into the ins and outs of genetics in this article! The problem starts during the early stages of development and CEA manifests because there is a mutation in the chromosomes partially responsible for the development of the eye. These mutated chromosomes lead to an underdevelopment of the back of the eye (the choroid and retina). The choroid layer especially contains the main blood vessels of the eye and it plays an important role in providing nourishment to the retina, ensuring optimum vision and ocular health.
Abnormal development of the choroid is the most common problem found in CEA patients. When the blood vessels in this part of the eye do not develop, this results in the nutrients and blood supply to the eye being dramatically impaired. This problem is known as ‘choroidal hypoplasia.’
In CEA patients, there may also be other ocular abnormalities which develop and there are sometimes more severe consequences, including retinal detachment. Retinal detachment is where their retina (the thin light-sensitive layer) at the back of their eye becomes loose, and unfortunately this can lead to complete blindness.
CEA is usually a bilateral condition, meaning that both eyes are usually affected.
What are the clinical signs?
- Vision impairment is the main clinical sign of CEA which you may see in your dog. However, the degree of vision loss is very much dependant on the severity of the condition and this can vary.
- Sometimes, dogs experience a sudden onset blindness and there may be no warning signs leading up to this. Blindness is the most common clinical sign of CEA. Signs of sudden onset blindness can often be really distressing for both your beloved dog and also you as the owner. Your dog may suddenly start to bump into objects/walls and may suddenly be hesitant to move around normally. I won’t discuss in too much detail in this article about how to manage a blind canine, however, it is extremely important to minimise changes in their environment and to provide ongoing support.
- A cloudy eye appearance can also be a sign of CEA.
- CEA can also lead to dogs being born with microphthalmia (abnormally small eyeballs) or enophthalmia (sunken in eyeballs).
How is it diagnosed?
Your vet will initially perform a full clinical examination and they will examine your dog’s eye with an ophthalmoscope, assessing all the layers of the eye. Furthermore, your vet may advise a referral to a Veterinary Ophthalmologist for further investigations. A definitive diagnosis is not possible without the aid of genetic testing, which thankfully is now available. Speak to your local vet to discuss what is involved with genetic testing and to explore this option further. If your dog is found to be carrying the genetic mutation responsible for CEA, it goes without saying that breeding these individuals is strongly advised against.
Is CEA treatable?
Sadly, CEA is not treatable and there is no known treatment to reverse this condition. This is why genetic testing is so important because we should be doing everything possible by breeding responsibly to reduce the risk of this genetic trait. Surgery may be performed by an ophthalmic surgeon to prevent or attempt to treat retinal detachment if this complication occurs.
Fortunately, CEA is not a life-threatening disease, but the presence of CEA will certainly affect the lives of both the dog affected and their owner. Dogs affected will require lifelong supportive care, lifestyle adaptations and regular vet visits.
Which dogs are affected?
Through genetic testing and awareness of the condition, the percentage of collies affected by this condition has dramatically reduced. It was estimated that 50 years ago, 90% of collies carried this genetic mutation (Yu-Speight, 2021). As mentioned earlier, this condition is still even today over-represented in collies, however, other dog breeds are known to be affected. Interestingly, these affected breeds include Australian shepherds, Shetland sheepdogs and Lancashire heelers. Some puppies are born with this condition, whereas in other dogs the signs and disease may manifest later in life.
To conclude, it is imperative to stress the importance and the value of genetic testing/screening prior to breeding at-risk dogs. We know that prevention is always better than cure in any scenario. Certain consequences of the condition can be managed, but once the disease has manifested there sadly isn’t a cure and affected canines will require lifelong support, hopefully this is an area likely to be explored even further within future veterinary research.