Collie eye anomaly (CEA) is an inherited eye condition in dogs where parts of the eye, particularly the layer of tissue behind the retina, don’t develop properly during fetal growth. It ranges from mild, with little to no impact on vision, to severe cases involving retinal detachment and blindness. The condition is present at birth and cannot be cured, but early screening and genetic testing can identify affected dogs and guide breeding decisions.
How CEA Affects the Eye
The hallmark of CEA is underdevelopment of the choroid, the network of blood vessels that nourishes the retina. In mild cases, this thinning (called choroidal hypoplasia) is the only defect, and the dog’s vision remains functional. But CEA can also involve more serious structural problems. A coloboma, which is a gap or hole near the optic nerve, weakens the back of the eye and can lead to retinal detachment over time. Some affected dogs develop bleeding inside the eye or abnormally small eyeballs. In the most severe cases, these complications result in significant vision loss or complete blindness.
The severity a dog is born with generally stays stable throughout life. A dog with mild choroidal hypoplasia won’t progress to retinal detachment later. However, dogs born with colobomas carry a lifelong risk that the retina could detach, so periodic eye exams are worthwhile for those cases.
Which Breeds Are Affected
CEA is most common in Rough and Smooth Collies, where prevalence can be strikingly high. Studies have found rates of 40.6% in Collies in the Netherlands, 72% in Smooth Collies in the United Kingdom, and as high as 83.3% in Rough Collies in Thailand. Shetland Sheepdogs, Border Collies, and Australian Shepherds are also affected, though at lower rates. One study testing Shetland Sheepdogs found 10% were affected, with another 40% carrying the gene without showing signs.
The condition is so widespread in some Collie populations that finding completely unaffected breeding stock can be challenging, which is part of why genetic testing has become essential for breeders.
The Genetics Behind CEA
CEA follows an autosomal recessive inheritance pattern, meaning a dog needs two copies of the defective gene to be affected. Dogs with just one copy are carriers: they appear normal but can pass the gene to their offspring. The mutation involves a deletion in a gene called NHEJ1, and genetic testing can identify all three states (clear, carrier, affected) with 90 to 95% accuracy.
If two carriers are bred together, roughly 25% of the puppies will be affected, 50% will be carriers, and 25% will be clear. Because carriers show no outward signs of the condition, DNA testing is the only reliable way to identify them before breeding.
Early Screening and Diagnosis
Puppies can be screened by a veterinary ophthalmologist as early as 5 to 6 weeks of age, with the ideal window falling before 12 weeks. This timing matters because retinal folds, one of the visible signs of CEA, can flatten out and disappear as the puppy matures. A dog examined after 12 weeks might appear normal on an eye exam despite actually being affected. This phenomenon is sometimes called “going normal,” and it’s one reason why a clean eye exam in an older dog isn’t always conclusive.
During the exam, the ophthalmologist dilates the puppy’s pupils and looks at the back of the eye for signs of choroidal thinning, colobomas, or retinal abnormalities. The exam is painless and takes only a few minutes per puppy. For breeders and buyers who missed the early screening window, a DNA test fills the gap. A simple cheek swab sent to a genetics lab can confirm whether a dog is clear, a carrier, or affected regardless of age.
Living With a CEA-Affected Dog
Most dogs with CEA have the mild form and live completely normal lives. Choroidal hypoplasia alone rarely interferes with a dog’s ability to navigate their environment, play, or work. Many owners of mildly affected dogs never notice any visual issues at all.
Dogs with more significant defects, particularly colobomas or retinal detachment, may need some environmental accommodations. Keeping furniture in consistent locations, using verbal cues instead of hand signals, and avoiding sudden changes to the home layout can help a visually impaired dog feel confident. Dogs adapt remarkably well to partial or even complete vision loss, relying more heavily on hearing and smell.
There is no treatment that corrects the underlying developmental defect. In rare cases where retinal detachment or intraocular bleeding occurs, a veterinary ophthalmologist may be able to intervene surgically, but these are rescue measures for complications rather than fixes for the root condition.
Preventing CEA Through Breeding
Because CEA is entirely genetic, the only way to reduce its prevalence is through informed breeding decisions. Dogs who carry the abnormal gene should ideally not be bred with other carriers. In breeds where the carrier rate is extremely high, breeders sometimes pair a carrier with a clear dog, which ensures no affected puppies are produced while maintaining genetic diversity. Over time, this approach gradually reduces the frequency of the mutation in the population.
If you’re buying a puppy from a breed at risk for CEA, ask the breeder for documentation of both the eye exam (performed before 12 weeks) and DNA test results for both parents. Responsible breeders test routinely and are transparent about the genetic status of their dogs.