Collie eye anomaly (CEA for short), also known as Choroidal Hypoplasia, is a genetic condition that can lead to vision impairment and blindness in Collies and other herding dogs. CEA in dogs is caused by a mutation in the gene that is responsible for eye formation and development in the womb, and can cause vision problems down the road for those dogs who have the gene.
Breeds who are affected by this mutation include rough and smooth-coated Collies, Border Collies, Australian Shepherds, Shetland Sheepdogs, Lancashire Heelers, and Nova Scotia Duck Tolling Retrievers.
What Is Collie Eye Anomaly?
As mentioned above, CEA is caused by an inherited genetic mutation that reduces the development of blood vessels in the eye that support the retina. The retina is a layer of tissue at the back of the eye which receives light and sends signals to the brain for visual recognition. A dog eyes diagram can illustrate the anatomy of the dog eye and the location of the retina and choroid at the back of the eye.
CEA is usually not diagnosed until the pet shows signs and symptoms, and as the disease progresses, it can lead to blindness. When a dog has CEA, it always occurs in both eyes (bilateral CEA) but may be less severe in one eye than the other.
CEA in dogs can be associated with several other abnormalities of the eye, and some are listed below:
- Microphthalmia. This condition occurs when the eyeball is smaller than normal. Microphthalmia in dogs can affect one or both eyes.
- Enophthalmia. This anomaly happens when the eyeballs are positioned deep into the eye sockets, giving a sunken appearance.
- Mineralization of the cornea. The cornea covers the front surface of the eye, and functions to refract or bend light. When the cornea is mineralized, there will be observable cloudiness over the eye.
- Detached retina. As blood flow through the eye is reduced, the retina does not receive adequate blood flow, and in some advanced cases can become detached from the rest of the eye. In some cases a detached retina in dogs can be corrected with surgery.
- Coloboma/Staphyloma/Ectasia: These terms all describe a bulging in the eyeball that usually occurs in the area of the optic disc.
Coloboma occurs during development where a seam called the optic fissure does not close completely.
Staphyloma is an abnormal protrusion of tissue through a weak point in the eyeball and occurs due to the weakening of the outer layer of the eye.
Ectasia happens when the inner layers of the cornea are weakened and bulge, distorting vision.
The severity of these conditions depends on the location of the bulge, and how it affects the dog’s vision. However, large colobomas or severe ectasia of the sclera (the white portion of the eye) can lead to retinal detachment.
What Can I Do For Collie Eye Anomaly?
Unfortunately, there is no cure for CEA. In Collies who have coloboma, laser surgery is an option to minimize the advancement of the condition. In cases of a detached retina, surgery may be an option as well. However, many dogs with this condition learn to adapt and can go on to live happy and healthy lives.
Can CEA Be Prevented?
Since CEA is a genetic disease, the best prevention is to avoid breeding dogs who carry the mutation. The good news is that there are tests available for CEA, which can be very useful for breeders. Although CEA typically leads to vision problems and blindness, many of these dogs adapt quite well to their vision loss, and it is possible to make some lifestyle changes to offer them assistance while navigating around the home.
How Is CEA Passed On?
CEA dogs have a mutation on chromosome 37. The mutation that carries the CEA gene is also recessive, meaning that it is a gene that must be present in both parent’s DNA to be passed on to the puppies. In these cases, chances are good that both parents will pass on the CEA gene to at least half of their offspring, but researchers are unsure of how the severity of symptoms is influenced.
Since the mutation is recessive, both parents may not be affected by the mutation, and may not show any signs or symptoms. However, they can pass it on to their offspring. There is speculation that other genes may be involved in CEA, which would explain why this disease can be more severe in some Collies and not so much in others.
What Are The Signs And Symptoms Of CEA?
CEA signs and symptoms vary according to the individual dog, but in some dogs vision changes are minor, whereas for others it leads to blindness or holes in different layers of the eye. If a dog experiences holes or spots, vision loss depends on the size and location of the holes and spots. Many owners may not notice any changes until vision has already been affected, but, a poorly developed choroid (the vascular layer of the eye) can be spotted as early as 5-8 weeks by a veterinarian.
Puppies and young dogs with Collie eye anomaly can show the following symptoms:
- Optic nerve coloboma
- Bilateral lesions on one or both eyes
- Corneal stromal mineralization
- Microphthalmos (small eye) or enopthalmos (posterior displacement of the eyeball)
- Retinal vessel tortuosity (dilated or twisted blood vessels)
- Retinals detachment, folds with or without intraocular hemorrhage
How Is CEA Diagnosed?
As mentioned above, a veterinary ophthalmologist can detect a thinning choroid in young puppies by using an ophthalmoscope (an instrument that can view the eye and all of its structures). For this reason, it’s important to have young puppies examined as early as possible. Thinning of the choroid, the presence of holes and spots, as well as retinal changes are best detected early since as puppies grow, these anomalies are harder to recognize.
Interestingly, blue merle varieties of Collies, Border Collies and Australian Shepherds typically lack pigment in the choroidal eye layer, and this can present a challenge to veterinarians as far as diagnosing CEA. These dogs are said to possess “merle eyes,” (which should not be confused with “blue eye” or “wall eye”). A wall eye is an eye with a streaked or opaque white iris. Merle eye is a color change in the iris, and can appear in a dogs with normal irises as well as in walled eyed dogs, or in dogs with blue irises.
What Is The Treatment For CEA?
If your dog shows the signs and symptoms of CEA, and vision loss, your veterinarian will perform a complete physical exam, a thorough eye exam, and may refer you to a veterinary ophthalmologist for additional evaluation and treatment. Unfortunately, there is no cure for CEA, but in some cases, laser therapy for coloboma, or surgery for a detached retina can be considered.
How Do I Manage CEA In My Dog?
For some conditions, such as coloboma or retinal changes, your dog should be monitored closely during the first 12 months of life, and every year after that to track any changes or possible retinal detachment. Regular examinations are important to track the progression of CEA, and your veterinarian can recommend how to effectively manage the disease, and how to keep your best friend as comfortable as possible.
Conclusion
Collie eye anomaly (CEA) is a genetic mutation that affects vision in Collies, Australian Shepherds, Shetland Sheepdogs, and a variety of other herding breeds. The mutation adversely affects the development of blood vessels in the eye and can be detected in puppies as early as in utero (still in the womb).
Although there is no cure for CEA, breeders are encouraged to have breeding pairs tested for the mutation, and to have all puppies evaluated by a veterinary ophthalmologist as young as 5 weeks. The good news is that many dogs with CEA can adapt quite well to the condition, and can live healthy and happy lives. If you have any questions about CEA, contact your veterinarian for more information.
