Collie eye anomaly in dogs – CEA

Overview

CEA stands for Collie Eye Anomaly, describing a structural abnormality of a Collie's eye. The condition particularly affects development of the choroid and sclera at the back of the eye.

Blood vessels in the choroid support the supply of oxygen and nutrients to the outer retina. The retina is a layer of nerve tissue at the back of the eye involved in vision.

Changes usually affect both eyes, but their severity may differ between eyes. In a dog without symptoms, the developmental abnormality may only be found during examination of the back of the eye.

CEA particularly affects Collie-related breeds, but is also diagnosed in other breeds.

The optic disc is the point through which signals from retinal nerve cells leave towards the brain.

Causes

Development before birth and inheritance

An inherited change affecting eye development can disrupt formation of several tissue layers at the back of the eye. The CEA-CH form assessed by DNA testing has autosomal recessive inheritance.

An affected dog therefore receives the associated gene variant from both parents. A carrier has the altered variant in only one gene copy, and carrying it does not itself cause this recessive disease.

A clinically healthy-looking carrier can nevertheless pass the variant to offspring.

CH, coloboma and retinal detachment

CH, or choroidal hypoplasia, means a localised, congenital underdevelopment of the choroid. The same mild CEA change is also referred to as CRD in examination results.

In optic disc coloboma, the embryonic optic fissure does not close normally, leaving a tissue defect. An extensive coloboma can predispose the retina to detachment from its supporting tissue.

Coloboma can also occur as an independent finding, so not every coloboma is part of CEA.

Risk factors

CEA occurs in both Rough and Smooth Collies. Other recognised risk groups include Shetland Sheepdogs, Border Collies and Australian Shepherds.

The condition is also diagnosed in Lancashire Heelers and Nova Scotia Duck Tolling Retrievers. Miniature American Shepherds and Bearded Collies are also breeds in which CEA is recognised as an inherited eye disease.

One breed-club account describes mild CH as a fairly common eye developmental abnormality in Rough Collies. It reports a relatively better CEA situation in Smooth Collies than in Rough Collies.

The condition has also been described in Boykin Spaniels and Longhaired Whippets, so the name does not limit it to Collies.

Australian Kelpies and Hokkaidos are also breeds in which CEA has been identified as an inherited eye disease.

Typical symptoms

Mild CH is usually symptom-free, so the absence of signs at home does not rule out CEA. If vision deteriorates, the following general signs of a vision problem may be noticed:

• Your dog bumps into objects or people while moving around.

• Using stairs becomes uncertain or your dog avoids them.

• Your dog hesitates when jumping onto or down from a familiar surface.

• A normal walk no longer appeals as much as before.

• Your dog cannot find a toy or food bowl by sight.

• An unfamiliar environment makes your dog less confident than usual.

Some dogs with CEA have abnormally small eyeballs, called microphthalmia. The eyes may also appear more deeply set in their sockets than usual.

Loss of vision in one eye can impair depth judgement and cause collisions on only one side.

A dog with impaired sight may search for a treat mainly by smell until their nose touches it. Locating a thrown toy may depend on the sound of it landing.

Complications and consequences

Mild findings and severe structural abnormalities

Mild CH does not progress as the dog grows into adulthood. However, a large optic disc coloboma can significantly impair vision through its size alone.

More severe coloboma changes are described in about 10–20% of dogs with CEA. Retinal detachment associated with CEA is estimated to occur in about 2–5%.

Bleeding inside the eye is another possible complication. Complete retinal detachment blinds the affected eye.

However, coloboma does not inevitably lead to detachment, especially if the finding remains stable during the first year of life. Retinal degeneration may develop in the detached area even if the retina later reattaches.

Diagnosis at the vet

Puppy examination before changes become hidden

A vet experienced in eye examinations examines the back of the eye with an ophthalmoscope. Some official screening schemes require a vet approved for that examination.

Puppies should be microchipped before the recommended 6–8-week eye examination. Pigment may conceal an area of CH in a puppy over ten weeks old, even though the developmental disorder has not healed.

In some puppies, concealment occurs before six weeks, when DNA testing helps clarify the situation. Concealed CH may be called 'go normal', which refers to a change in visibility.

A small coloboma is not always detected during a puppy check, so the finding may become clearer after one year of age.

What do the examination and DNA test investigate?

Eye drops dilate the pupils so that the vet can assess the internal structures closely. Besides the back of the eye, the examination includes the front, lens and other visible structures.

CH may appear as a pale or pink area beside the optic disc. A DNA test identifies the genetic change being tested for even in a dog without clinical eye signs.

The test can distinguish a carrier from a genetically clear dog, which ordinary external inspection cannot do. An individual DNA test examines a particular variant, rather than every possible inherited eye disease.

Depending on the laboratory, a sample may be blood or cells collected from the inside of the cheek. Incorrect labelling of DNA samples is a possible source of error, particularly when testing several dogs at once.

Careful sampling must prevent cheek-cell samples from becoming contaminated with another dog's DNA.

Official eye screening records

The dog's identification is checked during the examination so that the report is linked to the correct animal.

The report records the location and nature of findings so that later examinations can compare them with earlier observations.

Other tests for impaired vision

If corneal or lens opacity prevents a view of the back of the eye, ultrasound can examine the retina. In suspected acute detachment, blood pressure measurement and a general health examination help assess other possible causes.

CEA differs from progressive retinal atrophy, or PRA, in which cells involved in vision degenerate. Retinal detachment developing later may result from high blood pressure or eye trauma, for example, rather than CEA.

Treatment

Medication cannot correct the developmental disorder

Treatment cannot restore congenital CEA structural abnormalities to normal.

Treating retinal detachment

If retinal detachment develops, the vet chooses treatment according to its type and cause. An early, partial detachment associated with coloboma may be treated with laser surgery in some cases.

Laser can create a supporting boundary around a small retinal hole, a procedure called retinopexy. Repair of a detachment associated with a tear may require more complex surgery inside the eye.

Some tear-related detachments are repaired using cold treatment or an internal supporting fill as well as laser. Prompt treatment may reduce retinal damage caused by detachment.

If vision has been lost

Many visually impaired dogs adapt well and can enjoy a fulfilling daily life. Sudden sight loss may be a much harder change for a dog than gradually deteriorating vision.

If a blind eye remains painful, the vet may consider removing it to end the pain.

Prevention

Preventing CEA relies on breeding choices. DNA testing can identify carriers of the recessive variant before a mating is planned.

A carrier may be used cautiously only with a mate confirmed genetically clear for that particular variant. Removing all carriers from breeding at once can narrow a breed's genetic diversity and increase the importance of other inherited diseases.

Some breed-club guidance allows breeding from a dog with mild CH, preferably with an unaffected mate. Breeding from a dog with coloboma or retinal detachment is not recommended.

A CEA DNA test does not remove the need to examine a breeding dog's eyes for other conditions. Some Collie breeding health schemes require an eye examination in adulthood.

Eye examinations of dogs that will not be bred from also help identify inherited eye diseases within a breed.

Important for dog owners

Examination records and sampling

Keep the puppy eye examination report for later checks. Note which eye is affected and what the report says: CH, coloboma and detachment mean different things.

CEA diagnosed in puppyhood but later hidden is still recorded as affected, even when the finding is no longer visible.

In some screening reports, an 'undetermined' result means that findings may suggest the condition but are insufficient for definite classification.

A 'suspicious' result means slight findings that are nevertheless characteristic of that eye disease.

The recommended repeat examination depends on the finding; an uncertain finding in an adult may be reassessed after 12 months.

Follow the chosen laboratory's DNA sampling instructions, because its test may require a particular sample type.

Safe daily life for a visually impaired dog

Keeping furniture and routes unchanged at home makes navigation easier for a visually impaired dog.

Keep food and water bowls in the same places so that your dog can find them as usual.

Gates can prevent access to hazardous parts of the home.

Speak before touching your dog so that unexpected handling does not startle them.

Outdoors, a visually impaired dog is safest on a lead and should only be let off in a secure, fenced area.

Games based on smell and sound can support a visually impaired dog's activities.

Remove trip hazards from routes through the home and pad sharp corners if your dog can no longer see them.

If the layout must change, guide your dog along the new route several times to help them learn it.

Frequently asked questions

Does every dog with CEA go blind?

Mild choroidal hypoplasia, or CH, does not usually substantially impair vision, so a CEA finding does not automatically mean blindness. A large coloboma and retinal detachment are more serious findings that can impair vision or blind an eye.

Why are eyes examined when a puppy is so young?

CEA puppy screening is recommended at 6–8 weeks, when mild CH can often still be seen at the back of the eye. Later pigment accumulation may hide it, so a normal adult eye examination does not reliably establish that CH was absent earlier.

Does a DNA test replace an eye examination?

A DNA test checks a particular genetic variant; it is not a combined test for every eye disease. A clinical eye examination remains necessary because Collies can have other eye conditions besides CEA that must be considered in breeding.

Can a carrier be a healthy pet?

A carrier of the recessive CEA variant does not develop the disease because of that carrier status, although they can pass the variant to puppies. For breeding, a mate genetically clear for this variant is chosen, allowing use of the carrier to be balanced with disease prevention.

Can CEA be treated with surgery?

CEA's congenital structural abnormality cannot be restored to normal, so surgery does not cure the whole condition. Laser treatment may be considered in some cases of early partial retinal detachment associated with coloboma; the vet assesses suitability from the eye findings.