Collie Eye Anomaly
Collie Eye Anomaly (CEA) is an autosomal recessive inherited eye disease that affects many of the collie breeds, and is extremely prevalent in Rough and Smooth Collies, between 70 to 97% carry at least one mutation. (source: Animal Genetics UK) and the rate of affected dogs can be as high as 85-90%+. (source: OptiGen) CEA causes underdevelopment, or hypoplasia, in the eye under the retina (choroid). As such, all dogs with CEA have a degree of choroidal hypoplasia (CH) - which causes the choroid to appear pale due to thinning when viewed, leaving the sclera and vessels underneath visable.
Dogs with CEA will experience eyesight issues for the entirety of their life. Examples range in severity, with puppies who are affected often being tested clinically before 8 weeks and graded. This is often quoted as 'severe' CEA, 'mild' CEA, or 'clear' - however do not mix up clinically clear for genetically clear - clinically 'clear' dogs are still affected by CEA, but to a lesser extent at time of testing.
It is not a degenerative condition, though complications can occur, usually in the first few years of life. These can cause degeneration in eyesight or even blindness.
Some dogs affected with CEA may have colobomas around the optic nerve, caused by 'pits' in the tissue. In around 5-10% of dogs with CEA, retinal detachment or haemorrhage of blood vessels can even occur, which can cause blindness. (source: OptiGen)
A veterinary ophthalmologist usually diagnoses CEA clinically by observing the back of the eye in puppies under 8 weeks. Abnormalities such as CH and colobomas can then be observed.
At the age of 3 months, the retina becomes its final 'adult' colour, and this can hide the issues in the choroid (this is commonly observed in dogs said to 'go normal'). It is important to note this, and the importance of clinical tests before the dog reaches the age of 3 months. One study retested as adults puppies that were diagnosed with mild CEA before 3 months, and 68% had a fundus (back of eye) with normal appearance. (source: BVA, Hereditary Eye Disease in Dogs, 2017)
The BVA have a document with some fantastic images of the CEA affected eye, which can be found here.
A genetic test is also available to determine which dogs are affected by the trait.
There is no treatment or cure for CEA.
Labs can test for CEA in various ways, including buccal swab, blood tests (EDTA tube), or dewclaw samples. Check with your preferred lab which samples they require for this test.
CEA is a recessive disease, meaning dogs need two copies (homozygous mutant) of the mutant CEA gene to express the associated disorder. Carriers (Heterozygous) will not express the disease but can pass it onto offspring.
The below chart is a theoretical breeding calculator for CEA. Results in bold are results where the puppy will be affected by CEA. Results that are 'around' a percentage means that each puppy has the quoted percentage chance of that result. It does not mean that EXACTLY that percentage of the litter will have the result.
RESULTS IN PRACTICE
Although it can seem like the most ethical thing to do would be to never breed from affected dogs, erasing the majority of the gene pool would have a devastating result (please see Genetic Diversity section). Instead, ensure your breeding stock is tested, and work towards eliminating the condition with subsequent generations of dogs.