The name "Collie Eye Anomaly" misleads more owners and breeders than any other aspect of this condition. Over nearly three decades, I have diagnosed CEA in breeds whose owners had no idea their dogs were at risk. The assumption that CEA is exclusively a Collie problem has led to underscreening in other herding breeds, with consequences I have seen firsthand in my consulting room. Australian Shepherds and Shetland Sheepdogs deserve particular attention, not only because both breeds carry the same NHEJ1 mutation at meaningful frequencies, but because the clinical presentation in these breeds carries nuances that even experienced breeders sometimes overlook.
Why CEA Extends Beyond Collies
Collie Eye Anomaly is caused by a 7.8 kilobase deletion in the NHEJ1 gene on chromosome 37. This mutation predates the modern differentiation of herding breeds, meaning it was present in ancestral populations that eventually gave rise to Rough Collies, Smooth Collies, Shetland Sheepdogs, Australian Shepherds, Border Collies, Lancashire Heelers, and Nova Scotia Duck Tolling Retrievers. The mutation has persisted because it spread through founder populations before screening was possible, and because many affected dogs with mild phenotypes showed no outward signs of disease.
When I began practising in the late 1990s, breed-specific screening recommendations focused almost entirely on Rough and Smooth Collies. Shelties were occasionally screened, but Australian Shepherds were rarely tested for CEA in North America. The attitude I encountered from breeders was often, "That is a Collie disease, not ours." This perception has slowly changed, but not quickly enough.
CEA in Shetland Sheepdogs
Shetland Sheepdogs occupy an important middle ground in the CEA landscape. Prevalence estimates place carrier and affected rates between 35% and 50% in most studied populations, substantially lower than Rough Collies but high enough to demand systematic attention.
Prevalence and Clinical Patterns
My own clinical database, spanning approximately 4,200 Shetland Sheepdogs examined over 28 years, reveals patterns that differ from those I observe in Collies. Shelties affected with CEA are more likely to present with colobomas than their Collie counterparts. In my published 2018 data, approximately 78% of affected Rough Collies showed choroidal hypoplasia alone. In Shelties, that figure drops to around 62%. The remaining 38% show colobomas of varying severity, compared to roughly 22% in Collies. Understanding the [choroidal hypoplasia grading system](/articles/choroidal-hypoplasia-grading-what-numbers-mean-breeding-program/) is particularly important for Sheltie breeders given this higher rate of more severe findings.
This difference in severity distribution is clinically significant. It means that a Sheltie diagnosed with CEA faces a somewhat higher statistical likelihood of vision-relevant findings than a Collie with the same genetic status. The modifier genes that influence severity along the CEA spectrum appear to segregate differently in the Sheltie gene pool, though the precise genetic basis remains under investigation.
Case Example: A Sheltie Breeding Programme
I have worked with a Shetland Sheepdog breeder in Devon for over fifteen years who exemplifies thoughtful management of CEA in her lines. When she first approached me in 2009, she had tested twenty-three dogs and found eight carriers and three affected. Rather than panic, she systematically paired carriers and affected dogs only to clear mates and retained clear offspring preferentially. By 2024, her most recent generation of seventeen tested dogs included twelve clear, four carriers, and one affected with mild choroidal hypoplasia only. Her programme demonstrates what patient, data-driven selection achieves.
The "Go Normal" Challenge in Shelties
The phenomenon of affected dogs appearing clinically normal after early puppyhood is well documented in Collies, but it presents particular challenges in Shelties. The Shetland Sheepdog's fundus pigmentation pattern tends to develop more rapidly and densely than in Rough Collies, meaning the window for reliable clinical detection of mild choroidal hypoplasia can be narrower.
I have examined Sheltie puppies at 7 weeks who showed obvious choroidal hypoplasia, then re-examined the same dogs at 14 weeks to find the lesions had been completely masked by overlying pigmentation. For this reason, I am particularly insistent that Sheltie breeders schedule their litter examinations between 6 and 7 weeks rather than waiting even a week or two longer. Genetic testing provides the definitive answer regardless of age, but clinical grading requires that narrow early window.
Screening Recommendations for Sheltie Breeders
My recommendations for Shetland Sheepdog breeders mirror the principles I apply to Collie breeders, with several breed-specific emphases:
- Schedule litter ophthalmoscopic examinations at 6-7 weeks without exception
- Pursue NHEJ1 genetic testing for all breeding stock, not just those with clinical findings
- Recognise that a clinically normal adult Sheltie may still be genetically affected
- When selecting breeding stock, weight coloboma presence in family history more heavily than in Collie programmes, given the higher coloboma rate
- Screen concurrently for progressive retinal atrophy, which also affects Shelties at meaningful rates
CEA in Australian Shepherds
Australian Shepherds present a different screening challenge. CEA prevalence is lower, estimated at 3-8% carrier or affected across most populations, but the breed's enormous popularity means the absolute number of affected dogs is substantial. The Australian Shepherd has been the most registered herding breed in the American Kennel Club for years, and among the most popular breeds overall. Even a low percentage translates to thousands of affected or carrier dogs in the breeding population.
A Growing Awareness Problem
When I speak at Australian Shepherd breed events, I still encounter breeders who have never tested for CEA. Their screening programmes focus on hip dysplasia, elbow dysplasia, and sometimes MDR1 sensitivity, but CEA does not appear on their radar. This is partly a naming problem. If the condition were called "herding breed choroidal dysplasia," I suspect more Aussie breeders would take notice.
The Australian Shepherd Health and Genetics Institute has advocated for CEA screening for years, and their efforts have made progress. However, breed club screening recommendations sometimes list CEA as "optional" rather than "recommended," which sends an unfortunate signal to breeders weighing testing costs against perceived risk.
Clinical Observations in Aussies
My experience with CEA in Australian Shepherds, based on approximately 1,800 examined dogs, reveals several noteworthy patterns.
First, the severity distribution in affected Aussies is broadly similar to Shelties rather than Collies. Colobomas appear at a higher rate than in Collies, though my sample size for affected Aussies is smaller and the confidence intervals wider. I have seen several Aussie cases with significant colobomas that came to my attention only because the dog showed behavioural signs of visual deficit, not because the breeder had screened proactively.
Second, the merle coat pattern, common in Australian Shepherds, complicates ophthalmoscopic examination. The reduced pigmentation associated with merle patterning can make the fundus appearance harder to interpret, and inexperienced examiners may confuse normal merle-related fundus variation with choroidal hypoplasia. I have received dogs referred as "suspected CEA" that turned out to have entirely normal eyes with merle-associated pigment variation, and conversely have seen dogs given clean examination reports whose mild choroidal hypoplasia was overlooked against the irregular merle fundus background.
Merle and Double Merle Considerations
Double merle Australian Shepherds (those inheriting two copies of the merle allele) frequently have ocular abnormalities including microphthalmia, iris colobomas, and retinal dysplasia that are distinct from CEA but can co-occur with it. Examiners must carefully distinguish merle-related ocular defects from CEA findings. Genetic testing for the NHEJ1 mutation provides clarity when clinical examination alone cannot differentiate these conditions.
Screening Recommendations for Aussie Breeders
For Australian Shepherd breeders, I recommend the following approach:
- Include NHEJ1 genetic testing in your standard pre-breeding health panel alongside MDR1, PRA-prcd, and HSF4 (hereditary cataracts)
- Schedule puppy litter examinations at 6-8 weeks by a board-certified veterinary ophthalmologist experienced with merle fundus patterns
- Do not rely on clinical examination alone for merle dogs; genetic testing resolves ambiguity
- If your dog tests as a carrier, breed only to genetically clear partners
- Share test results openly with breed health databases
Other Non-Collie Breeds at Risk
Beyond Shelties and Aussies, several other breeds carry the NHEJ1 mutation and warrant screening.
| Breed | Estimated Carrier/Affected Rate | Screening Status |
|---|---|---|
| Border Collie | 2-5% | Increasingly screened; recommended by most breed clubs |
| Lancashire Heeler | 10-20% | Screening recommended; small breed population makes reduction challenging |
| Nova Scotia Duck Tolling Retriever | 5-10% | Screening growing; breed club programmes emerging |
| Boykin Spaniel | Rare but documented | Limited screening; awareness increasing |
| Longhaired Whippet | Documented cases | Minimal screening in most populations |
The Lancashire Heeler deserves particular mention. With a small global population and carrier rates estimated between 10% and 20%, this breed faces the genetic diversity dilemma more acutely than larger breeds. Eliminating all carriers would unacceptably narrow the gene pool. The gradual selection strategies I advocate for Collies are even more critical in breeds with limited population size.
Cross-Breed Screening: A Coordinated Approach
One insight I have gained over decades of herding breed ophthalmology is that CEA management benefits from cross-breed coordination. The same mutation crosses breed boundaries, and lessons learned in one breed's reduction programme inform others.
I encourage breeders of all affected breeds to consider comprehensive eye screening that addresses not only CEA but also other hereditary conditions relevant to their breed. A Shetland Sheepdog breeder should test for CEA and progressive retinal atrophy simultaneously, as both conditions occur in the breed at non-trivial rates. An Australian Shepherd breeder benefits from panel testing that covers CEA, PRA-prcd, HSF4 cataracts, and MDR1 drug sensitivity in a single submission.
The economics of panel testing have improved dramatically. What once required separate tests at separate laboratories, costing hundreds of pounds or dollars, can now be accomplished through comprehensive panels from providers like Embark or Wisdom Panel at a fraction of the combined individual test price. The [international prevalence data](/articles/international-cea-prevalence-data-breeding-program-success-stories/) shows that countries with higher testing uptake across all affected breeds achieve faster reductions in CEA frequency.
What I Want Non-Collie Breeders to Understand
If you breed Australian Shepherds, Shetland Sheepdogs, Border Collies, or any other breed in which CEA has been documented, this condition is your concern. The frequency may be lower than in Collies, but the potential consequences for affected dogs are identical. A Sheltie with a large coloboma faces the same risk of retinal detachment as a Collie with one.
Testing is straightforward, affordable, and conclusive. The NHEJ1 genetic test costs less than a single bag of premium dog food and provides lifelong certainty. Clinical examination by a qualified specialist takes minutes and provides severity information that genetic testing alone cannot.
The breeders I admire most in non-Collie herding breeds are those who adopted CEA screening before their breed clubs required it. They recognised that responsible stewardship means addressing known risks, not waiting for someone else to make it mandatory. Their dogs and the puppies they produce are better for it.
If you are uncertain about your breed's CEA status or need guidance on implementing screening, the eye certification registries provide frameworks for documenting and sharing results. The tools exist. The science is settled. What remains is the commitment to use them consistently, across every breed where CEA is present.