Collie Eye Anomaly

TL;DR. Collie Eye Anomaly is a congenital, inherited eye condition in Collies and Shetland Sheepdogs that causes abnormal development of the choroid (the eye's vascular layer), sometimes leading to vision impairment or retinal complications.

Collie Eye Anomaly is a congenital condition that primarily affects herding breeds like Collies.

What is it?

Collie Eye Anomaly (CEA), also known as Collie eye syndrome, is a heritable congenital ocular defect. This means affected dogs are born with the condition due to genetic factors. The disease primarily impacts the development of the back of the eye, specifically the choroid, which is the vital layer of blood vessels that lies between the retina and the white of the eye (the sclera).

In a healthy dog, the choroid plays a crucial role in maintaining vision. As noted in a leading veterinary anatomy textbook:

"form the middle-sized vessel layer, which leads to and empties the choroidal capillary layer, which in turn nourishes the outer layers of the retina."

In dogs with Collie Eye Anomaly, this vascular layer fails to develop normally. This underdevelopment is called choroidal hypoplasia. Because the choroid is thin and lacks its normal network of blood vessels, the retina does not receive proper nourishment in the affected areas. Additionally, the disease is characterized by defects in the choroidal vasculature (abnormal, malformed blood vessels) and colobomata—pits or holes in the structures of the eye, such as the optic disc, which result from the failure of the embryonic optic fissure to close completely during development.

To understand how this occurs, it helps to look at how a dog's eye forms in the womb. Early in embryonic development, the eye begins as a simple structure:

"The first indication of the formation of the eye is seen as an optic sulcus on the neural fold rostral to the notochord on each side. The neuroectoderm surrounding this sulcus proliferates rostrolaterally to form the optic vesicle, a hollow diverticulum of the prosencephalon."

If the subsequent closure of the optic fissure is disrupted, a coloboma forms. Depending on the severity of these developmental errors, a dog may have normal vision, mild nearsightedness, or, in severe cases, complete blindness due to retinal detachment or bleeding inside the eye.

Causes & risk factors

Collie Eye Anomaly is a strictly hereditary condition. It is caused by an autosomal recessive genetic mutation, meaning a puppy must inherit a copy of the mutated gene from both parents to be affected.

Because it is a genetic defect present from conception, there are no environmental triggers or lifestyle factors that cause CEA. The primary risk factor is breed pedigree. The condition is highly prevalent in specific herding breeds, most notably:

• Collies (both Rough and Smooth varieties)
• Shetland Sheepdogs (Shelties)

Dogs carrying only one copy of the mutated gene (carriers) will not show clinical signs of the disease but can pass the mutation on to their offspring. If two carriers are bred, there is a 25% chance that each puppy in the litter will be clinically affected by CEA.

Signs to watch for

Because Collie Eye Anomaly is congenital, the structural defects are present at birth. However, because many affected dogs have mild forms of the disease, they may show no outward signs of vision loss. Owners often do not realize their dog has the condition unless a veterinary ophthalmologist performs a specialized exam.

When symptoms do manifest, they can include:

• Choroidal vasculature defect (Cardinal): Malformed, twisted, or sparse blood vessels in the back of the eye, visible only during an eye exam.
• Choroidal hypoplasia (Common): Pale, thin areas in the back of the eye where the underlying sclera (the white outer coat of the eyeball) shows through the underdeveloped choroid.
• Coloboma (Common): Pits or holes in the optic nerve or adjacent tissues. Large colobomas can severely compromise the structural integrity of the eye.
• Myopia (Occasional): Nearsightedness. Affected dogs may have difficulty focusing on distant objects. In the canine eye, focusing relies on the lens changing shape:

"The lens is the only structure capable of changing its refractive power. The most widely espoused paradigm for mammals is as follows: In the resting state, the lens is maintained in a relatively flattened configuration by the intrinsic elastic tension exerted on its equator by the ciliary body acting through the zonular fibers."

Structural distortions in the back of the eye caused by CEA can alter the eye's shape, leading to refractive errors like myopia.

An ophthalmoscopic exam reveals the abnormal blood vessels and pale patches characteristic of Collie Eye Anomaly.

While mild CEA is non-progressive (it does not get worse as the dog ages), severe cases can lead to secondary, vision-threatening complications. Emergency signs that require immediate veterinary attention include:

• Sudden blindness or apparent disorientation
• Dilated pupils that do not shrink when exposed to light
• Bumping into walls or furniture
• Visible blood inside the front chamber of the eye (hyphema)
• Signs of eye pain, such as squinting, tearing, or rubbing at the face

These acute signs typically point to a retinal detachment or intraocular hemorrhage, which are severe complications of large colobomas.

How vets diagnose it

Your vet or a veterinary ophthalmologist will diagnose Collie Eye Anomaly using ophthalmoscopy. This is a non-invasive examination of the interior of the eye using an ophthalmoscope, which allows the practitioner to visualize the retina, optic nerve, and underlying choroid.

To perform a thorough exam, the vet will first apply dilating eye drops to widen your dog's pupils. Once the pupils are dilated, the vet will use an indirect ophthalmoscope and a handheld lens to examine the fundus (the back of the eye). They will look for the classic hallmarks of CEA: pale patches of underdeveloped choroid, abnormal blood vessels, and colobomas.

Timing is critical for this diagnostic exam. The gold standard is to screen puppies between 5 and 8 weeks of age. During this brief window, the puppy's eyes are "optically clear." As dogs mature, pigment develops in the retina and a reflective layer called the tapetum lucidum matures. In mildly affected dogs, this normal development can mask the underlying choroidal hypoplasia—a phenomenon known as "go-normal." While these dogs still have the genetic defect and the underlying structural anomalies, they can no longer be diagnosed via visual examination later in life.

In dogs with naturally low pigment, the structures remain easier to see throughout life, as noted in veterinary anatomy literature:

"The short posterior ciliary arteries pass through the sclera adjacent to the optic nerve and ramify in the choroid... In dogs with poorly pigmented ocular fundi, the choroidal vessels are more easily visualized."

However, early screening remains the most reliable clinical method to identify affected puppies.

Treatment options

Currently, there is no treatment or cure that can reverse the primary developmental defects of Collie Eye Anomaly. The choroidal hypoplasia and colobomas a puppy is born with will remain for the rest of its life.

Monitoring and Support

For the vast majority of dogs with mild CEA, no treatment is necessary. These dogs typically retain excellent, functional vision and adapt perfectly to their mild structural defects. Regular annual veterinary eye exams are recommended to monitor for any signs of progression or complications.

Surgical Intervention for Complications

In severe cases where large colobomas put the dog at high risk for retinal detachment, advanced interventions may be considered. A veterinary ophthalmologist may utilize:

• Laser surgery (photocoagulation): Used to create tiny scars around a partial retinal tear to prevent it from progressing to a full detachment.
• Cryosurgery (freezing therapy): Similarly used to secure the retina to the underlying tissues.

If a complete retinal detachment or severe intraocular bleeding occurs, surgery is rarely successful in restoring vision, and therapy focuses on maintaining comfort. If a blind eye becomes painful or develops secondary glaucoma, surgical removal of the eye (enucleation) may be required to ensure the dog's quality of life.

Prognosis

Specific long-term prognosis statistics and quantitative survival data for Collie Eye Anomaly are limited in official records. However, the general clinical outlook for dogs diagnosed with CEA is highly favorable.

Because the primary lesions of CEA are congenital and non-progressive, a dog diagnosed with mild choroidal hypoplasia at 6 weeks of age will generally have the same mild defect at 10 years of age. Their vision is unlikely to deteriorate over time, and they will live a normal lifespan with an excellent quality of life.

For the small percentage of dogs born with severe colobomas, the prognosis for vision is guarded. These dogs are at risk for retinal detachment and hemorrhage, which usually occur within the first two years of life. Even if vision is lost in one or both eyes, blind dogs can navigate their home environments remarkably well and live happy, pain-free lives with appropriate environmental modifications.

Prevention

Because Collie Eye Anomaly is an inherited genetic disease, it cannot be prevented through lifestyle changes, vaccines, or diet. Prevention relies entirely on responsible breeding practices.

Genetic Testing

A highly accurate DNA test is commercially available to detect the mutation responsible for CEA. This test can identify:

• Clear dogs: Those with two normal genes.
• Carrier dogs: Those with one normal gene and one mutated gene (they will not show symptoms but can pass the gene to offspring).
• Affected dogs: Those with two mutated genes.

Breeders should perform DNA testing on all breeding stock. Carriers should only be bred to clear dogs to ensure that no affected puppies are produced. Affected dogs should be removed from breeding programs entirely.

Puppy Screening

All Collie and Shetland Sheepdog litters should undergo ophthalmoscopic screening by a board-certified veterinary ophthalmologist between 5 and 8 weeks of age. This ensures that even "go-normal" dogs are identified and documented before their adult eye pigmentation masks the defect.

When to call your vet

If you own a Collie, Shetland Sheepdog, or a mix of these breeds, you should schedule a routine ophthalmic exam to establish whether they are affected by CEA.

You must contact your vet immediately or seek emergency veterinary care if you notice any of the following red flags:

• Sudden loss of vision (your dog starts bumping into walls, cannot find their food bowl, or seems hesitant to move in low light)
• A cloudy or bluish appearance to the eye
• Visible blood inside the eye
• Squinting, rubbing at the eye, or keeping the eye tightly shut
• One or both pupils remaining widely dilated even in bright light

These signs can indicate acute retinal detachment or internal bleeding, which require immediate medical assessment to manage pain and preserve remaining vision.

For specific breeds

Collie Eye Anomaly is deeply tied to the history of the Collie and the Shetland Sheepdog. In these breeds, the mutation has historically been highly prevalent, with some estimates suggesting a significant portion of the population carried at least one copy of the gene before genetic testing became widely available.

If you are purchasing a Collie or Sheltie puppy, always ask the breeder for the CEA genetic test results of the parents, as well as the veterinary ophthalmologist's screening report for the litter. Reputable breeders will gladly provide this documentation to prove their puppies are free from severe congenital eye defects.

Sources

• Miller and Evans, Anatomy of the Dog, 5th Edition, p. 1686 (Embryonic eye development and the optic vesicle).
• Miller and Evans, Anatomy of the Dog, 5th Edition, p. 1708 (Structure of the choroid and retinal nourishment).
• Miller and Evans, Anatomy of the Dog, 5th Edition, p. 1730 (Lens physiology and accommodation).
• Miller and Evans, Anatomy of the Dog, 5th Edition, p. 1773 (Choroidal vasculature and ocular fundus pigmentation).