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The many causes of conjunctivitis in dogs

The key is to recognize and treat the underlying condition

[From Tufts January 2011 Issue]

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Dry eye, a common cause of conjunctivitis known as keratoconjunctivitis sicca, is especially prevalent in miniature schnauzers.

Conjunctivitis is a common eye problem in dogs, but that doesn’t mean it’s necessarily a simple one to treat. Quite often, the condition is a symptom of a potentially more serious problem. It occurs when the conjunctiva, the very thin layer of clear tissue on the outer surface of the eye, becomes inflamed, resulting in what’s colloquially known as pink eye.

“The inflammation is usually secondary to another problem, often a lid abnormality or dry eye,” says ophthalmologist Chris Pirie, DVM, at Cummings School of Veterinary Medicine at Tufts University. “The key is to recognize and treat the underlying cause.”

While it might be readily apparent to owners when their dogs’ eyes become irritated, diagnosing the underlying cause requires a veterinary exam. The possible causes of conjunctivitis are numerous. They include:
- Eyelid abnormalities or infections
- Disorders affecting the tear ducts or tear production
- Bacterial or viral infections
- Allergies
- Exposure to eye irritants
- Trauma to the eye
-Diseases that can affect the conjunctiva itself

Generally speaking, conjunctivitis is not life threatening. However, certain underlying causes can be quite serious and can affect other structures in the eye, as well as other parts of the body. For example, severe infections or injuries to the eye could lead to vision loss. Likewise, conjunctivitis could be a symptom of serious systemic disease, such as canine distemper. Certain infectious causes of conjunctivitis can be transmitted to other dogs.

Due to the wide range of causes, Dr. Pirie says it’s nearly impossible to quantify how likely it is that a dog will develop conjunctivitis in his lifetime. But it’s safe to say that it is one of the most common conditions he sees in his patients.

Breed disposition
Cases of conjunctivitis aren’t confined to certain breeds; however, some types of dogs might be more likely to develop it. “The risk is dependent on what the underlying cause is, and there are breeds at risk for each possibility,” Dr. Pirie says.

For example, dry eye — formally known as keratoconjunctivitis sicca, or KCS — is a common cause of conjunctivitis, and the condition is particularly prevalent in cocker spaniels, bulldogs, miniature schnauzers and West Highland white terriers. Meanwhile, entropion — an inner rolling of the eyelid edges that often leads to conjunctivitis — affects chow chows, shar-peis and others.

During the diagnostic evaluation, the veterinarian might perform several tests, in addition to a general physical and a thorough examination of the conjunctiva and eyelids. For example, if the veterinarian suspects that a dog has an abrasion or ulcers of the cornea, a fluorescein eye stain test might be performed. Likewise, a Schirmer tear test might be done to gauge whether the dog’s eye is producing enough tears. Additional tests might include bacterial cultures, glaucoma tests or blood tests designed to detect other underlying diseases.

Treatment, of course, depends upon the cause the veterinarian uncovers. If allergies are suspected, anti-inflammatory medications will likely be prescribed. In the case of an infection, bactericidal or fungicidal ointments might need to be applied to the eye. Removal of an irritating foreign body might require a quick general anesthesia to allow the material to be removed without risk to the eye.

The costs and prognosis vary greatly, Dr. Pirie says. If the underlying cause of conjunctivitis is an eyelid abnormality like entropion, surgery might be required to correct the problem, in which case the cost of treatment could cost several hundreds of dollars.

Regardless, all cases of conjunctivitis should be treated as soon as possible. The quicker a dog receives veterinary care, the quicker he’ll be on the road to recovery and the less likely he is to develop serious complications that might arise as a result of the underlying problem.

Lori Luechtefeld is a writer in Los Angeles.