Collie Eye Anomaly (CEA): What Every Herding Breed Breeder Needs to Know

CEA ranges from minor structural abnormalities to blindness — and DNA testing lets breeders prevent it

Collie Eye Anomaly (CEA) is one of the most common inherited eye conditions in herding breeds. It has been present in Collie populations for generations and has spread to related breeds. While many affected dogs have mild cases that do not significantly impair vision, severe cases can cause blindness. Understanding CEA genetics allows breeders to make informed decisions and reduce its prevalence over generations.

What Is CEA?

CEA is a congenital condition — dogs are born with it — affecting the development of the choroid, the layer of blood vessels that nourishes the retina. The underlying cause is a mutation in the NHEJ1 gene (also sometimes referred to as the CEA gene or choroidal hypoplasia mutation), which disrupts normal choroid development during fetal development.

CEA is always bilateral — it affects both eyes — though severity may differ between the two eyes.

CEA Severity Grades

CEA exists on a spectrum:

Choroidal Hypoplasia (CH) — The mildest form. The choroid is thinner than normal, with fewer blood vessels. In mild cases, this causes no functional vision impairment. Most dogs with CH-only CEA lead normal lives. CH is the most common form.

Coloboma — A pit or hole in the optic disc or surrounding area. Ranges from small and inconsequential to large and vision-affecting. Posterior colobomas can be serious.

Retinal Detachment — The retina separates from the choroid. Can cause significant vision loss to complete blindness in the affected eye. This is the most serious CEA complication.

Optic Nerve Hypoplasia — Underdevelopment of the optic nerve. Can cause vision deficits.

Most CEA-affected dogs have mild CH only and are not visually impaired. A smaller percentage have colobomas, and a small fraction experience retinal detachment.

The "Go Normal" Phenomenon

One of the most confusing aspects of CEA is the so-called "go normal" phenomenon. In puppies with very mild CH, the choroidal hypoplasia may become invisible on ophthalmoscopic exam as the puppy matures — not because the condition resolved, but because increasing pigmentation in the tapetum covers the lesions.

This is why CAER (previously CERF) eye exams for CEA should be performed at 6-8 weeks of age in puppies before the tapetum matures and obscures mild lesions. A dog that "goes normal" by adulthood is still genetically affected and can still pass CEA to offspring. DNA testing does not have this limitation — it reveals genetic status at any age.

Breeds Affected by CEA

CEA is most prevalent in:

• Rough and Smooth Collies — CEA is extremely widespread; prevalence has historically been very high
• Shetland Sheepdogs (Shelties)
• Border Collies
• Australian Shepherds
• Bearded Collies
• Lancashire Heelers
• Nova Scotia Duck Tolling Retrievers (a different mutation)

Genetics and Inheritance

CEA is autosomal recessive:

• Normal (N/N) — No copies of the CEA mutation. Will not develop CEA. Cannot pass the mutation.
• Carrier (N/CEA) — One copy. Eyes are normal. Can pass CEA to 50% of offspring.
• Affected (CEA/CEA) — Two copies. Will have some degree of choroidal hypoplasia at minimum.

Because carrier frequency is very high in Collies and Shelties (historically estimated above 80% in some populations), completely eliminating CEA from these breeds while maintaining genetic diversity is not practically achievable in the short term. The focus for most breed clubs is on preventing severely affected dogs while gradually working toward lower overall prevalence.

DNA Testing for CEA

DNA testing (Embark, Paw Print Genetics, Optigen) detects the NHEJ1 mutation reliably in Collies, Shelties, Border Collies, and Australian Shepherds. The test can be performed at any age from a blood or swab sample, and it is not affected by the "go normal" phenomenon.

Results:

• Normal — No copies; will not develop CEA; cannot pass mutation
• Carrier — One copy; eyes normal; can pass mutation
• Affected — Two copies; will have CEA changes in the eyes

Breeding Recommendations

Clear to Clear — Ideal; produces all Normal or Carrier offspring (if one parent was a carrier), or all Clear offspring (if both are truly N/N).

Clear to Carrier — Acceptable; produces approximately 50% Normal, 50% Carrier, no Affected.

Carrier to Carrier — Produces approximately 25% Normal, 50% Carrier, 25% Affected. Avoid.

Affected to Any — Avoid; produces Carrier or Affected offspring entirely.

Summary

CEA is a congenital eye condition caused by a mutation in NHEJ1, affecting choroid development in herding breeds. Most affected dogs have mild CH only and retain good vision; severe cases cause colobomas or retinal detachment. Early puppy eye exams (6-8 weeks) are important because mild lesions can become invisible as dogs mature. DNA testing is not affected by this "go normal" issue. Test breeding dogs, breed Clear to Clear or Clear to Carrier, and gradually reduce CEA prevalence in your program.