Conjunctivitis in Dogs

Overview of Canine Conjunctivitis

Conjunctivitis is an inflammation of the conjunctiva, which is the tissue coating the eye and lining the eyelids. Normally, the conjunctiva is moist and glistening with tiny blood vessels coursing through the semilucent tissue. It serves as a protective barrier for the dog’s eye by trapping debris and helping to prevent invasion of viruses and bacteria.

Conjunctivitis is a common eye problem in dogs. It may be the only eye disease present, or may be associated with other diseases or eye problems.

Causes of Conjunctivitis in Dogs

• Viral infections that affect the eye, such as canine distemper
• Bacterial eye infections
• Certain parasites of the conjunctiva or eyelids
• Corneal diseases
• Disorders of the tear ducts or of tear production
• Eyelid infections or abnormalities
• Exposure to foreign material such as plant material, fibers, sand and chemicals
• Trauma
• Allergies
• Idiopathic, meaning that no cause is ever defined
• Other illnesses, such as skin diseases, that can affect the eyelids and conjunctiva

What to Watch For

• Redness of the eyes
• Eye discharge
• Swelling of the conjunctiva
• Squinting or excessive blinking
• Occasional pawing or rubbing at the eyes

Diagnosis of Conjunctivitis in Dogs

Conjunctivitis is usually diagnosed based on physical exam findings. Your veterinarian will probably perform the following tests:

• Fluorescein staining to detect superficial abrasions or ulcers on the cornea
• Schirmer tear test to determine if your dog is producing sufficient tears
• Thorough exam of the conjunctiva, external eyelids and the third eyelid

In some situations, additional tests may be recommended, such as:

• Bacterial cultures
• Tests for distemper virus
• Tonometry, which measures eye pressure (glaucoma test)
• Conjunctival scrapings to evaluate the cells of the conjunctiva
• Conjunctival biopsy (rarely performed)
• Certain blood tests if the animal is also ill

Treatment of Conjunctivitis in Dogs

Treatment involves symptomatic therapy for the conjunctivitis and specific therapy for any underlying causes.

• The eye may be thoroughly irrigated to remove any irritating substance.
• Foreign material should be removed.
• Tear production abnormalities are treated with medication.
• Eyelid infections and abnormalities may require either medication or surgery.
• Since secondary bacterial infections are a common concern, antibacterial eye ointment is frequently prescribed.
• In many cases, anti-inflammatory eye medications are also indicated.

Home Care and Prevention for Dogs with Conjunctivitis

If you suspect that your dog has foreign matter in the eye, flushing with sterile eye irrigation solution can help dislodge the offending material. If flushing the eye is not possible or effective, prompt examination by a veterinarian is recommended.

Once diagnosed and started on medications, the eyes should be checked frequently for improvement. Most cases of conjunctivitis improve within 24 to 48 hours after medication is begun. If you notice that your dog is not improving, consult your veterinarian.

Unfortunately, many causes of conjunctivitis are not preventable, but veterinary examination and treatment usually resolves the disease rapidly and maintains your dog’s eyes and vision. To prevent conjunctivitis due to foreign matter in the eye, try to prevent exposure to potentially damaging items. Be very careful when bathing your dog to prevent shampoo from getting in the eyes.

Information In-depth for Dogs with Conjunctivitis

Canine conjunctivitis is a common eye ailment. It may occur alone or secondary to another eye disease. Finding and treating the underlying eye problem can prevent or diminish future episodes of conjunctivitis. In some instances no cause is ever defined for the conjunctivitis, but there are a variety of diseases that can produce conjunctivitis.

• Keratoconjunctivitis sicca (KCS or dry eye). With KCS there is inadequate production of the watery component of the tears. As a result, the surface of the eye becomes dry, irritated, inflamed, and infected. Signs of dry eye include a thick, ropey mucus-type discharge, corneal scarring, and sometimes squinting. The conjunctiva is usually red and inflamed.
• Upper respiratory diseases, as with kennel cough. These infections involve both bacteria and viruses. Signs of conjunctivitis are often present in both eyes, and other signs such as coughing, sneezing, nasal discharge, lethargy, fever and decreased appetite may be noted.
• Mechanical irritation. Usually this chronic irritation is due to problems in the development of eyelid and eye lashes. Eyelids may be rolled inward, which causes the eyelashes to rub continuously against the cornea. Loose and drooping eyelids may not be able to close completely and may lead to dry eye. Some dogs may have eyelashes that grow in the wrong direction and rub against the cornea. Some dogs may even have eyelashes that grow from areas other than the eyelids, which may be directed at the cornea and cause constant irritation.
• Foreign matter. Pieces of sand, plastic, metal, or grass can lodge under the eyelids and create a profound irritation of the eye.
• Environmental irritants. Cigarette smoke, dust, exhaust fumes, household chemicals, lawn and garden sprays, pollen and other plant material, may cause conjunctivitis. Such irritants may cause a certain type of conjunctivitis, called follicular conjunctivitis, particularly in young, growing dogs.
• Infection and inflammation of the eyelids and cornea. Because the conjunctiva is physically adjacent to both the eyelids and the cornea, any infection or inflammation of these tissues may result in conjunctivitis. Examples include corneal ulcers, certain forms of keratitis, blepharitis (inflammation of the eyelids), and skin diseases that affect the eyelids.
• Allergies. Allergy-related conjunctivitis is common in the dog and is most often associated with atopy (inhalant allergies). With allergic conjunctivitis, the conjunctiva becomes red, the eyes are often itchy, and watery discharge may be seen.
• Parasites. Parasites on the surface of the eye are rare in North American, but occasionally the Cuterebra fly larva may grow near the eye, or small Thelazia worms may occur on the surface of the eye.
• Primary bacterial infections. Without associated eye disease, these infections are a rare cause of conjunctivitis. It is much more common for bacteria to take advantage of inflamed conjunctiva, and then to invade this inflamed tissue to create a secondary infection.
• Trauma to the conjunctiva, eyelids, cornea or eye itself.
• Inflammation from within the eye. Occasionally outward extension of inflammation can reach the conjunctiva, resulting in conjunctivitis. In these instances inflammation within the eye is the primary concern.
• Any illness. Conjunctivitis may also develop anytime a dog is ill and not feeling well. Discharge from the eyes is common in diseases causing lethargy and fever.

Diagnosis In-depth of Canine Conjunctivitis

Diagnosing conjunctivitis is based on the physical exam finding of a red, inflamed conjunctiva with associated tearing or other eye discharge. Diagnosing the underlying cause in order to provide correct treatment is sometimes difficult. Your veterinarian will probably perform the following:

• A thorough eye exam to detect any foreign material such as sand, plastic or grass. It can also detect any abnormal eyelid conformation, abnormal eyelashes, eyelid inflammation and disorders of the cornea.
• An eye pressure test to detect glaucoma. This eye disease produces enlargement of the blood vessels under the conjunctiva and can easily be mistaken for conjunctivitis.
• Schirmer tear test to determine if your dog’s eyes produce an adequate amount of tears. Inadequate tear production results in keratoconjunctivitis sicca (dry eye), which causes conjunctivitis.
• Fluorescein staining to reveal corneal lesions. The test is done by placing a drop of dye on the surface of the eye, then flushing so the eye can be examined. If stain is present on the surface of the eye, there has been disruption of the cornea, such as an abrasion, scratch or ulcer.

In addition to these tests, your veterinarian may recommend additional tests.

• Conjunctival scraping and examination of the conjunctival cells to help identify the type of inflammation present
• Bacterial cultures
• Certain blood tests if the animal is acting ill

Treatment of Canine Conjunctivitis

Since many cases of conjunctivitis are mild and respond to topical anti-inflammatory medications, your veterinarian may chose to prescribe such a drug before proceeding with additional diagnostics. If the conjunctivitis does not resolve in five to seven days, or if it recurs immediately after the medication is stopped, further tests may be needed.

IF an exact cause can be determined, the specific treatment is instituted for that cause.

• For keratoconjunctivitis sicca or dry eye, artificial tears and lubricants are started. Topical antibiotics may also be needed initially to resolve any bacterial infection or concurrent corneal ulcer. In some cases, tear production can be increased with the use of topical cyclosporine. Treatment for dry eye is typically long term and repeated episodes of conjunctivitis may occur.
• Conjunctivitis associated with upper respiratory infections are usually treated with topical antibacterial medications. Supportive care and oral antibiotics may be indicated for other symptoms.
• Abnormal eyelid conformation usually requires corrective surgery. After surgery, the eye disease and conjunctivitis usually do not recur.
• Abnormal eyelashes are treated with surgery, freezing or a form of cautery. Simply plucking the offending eyelash is not recommended as the eyelash will grow back and may grow in longer and more rigid than before.
• Eye irritants such as pieces of sand, plastic, or grass can be flushed out of the eye using copious amount of sterile eye irrigation fluid. After removal of the offending foreign matter, a brief course of antibiotics and anti-inflammatories usually resolve the conjunctivitis.
• Conjunctivitis due to environmental irritants can be difficult to treat unless the irritant can be removed. Owner’s should avoid smoking around the dog, should avoid the use of spray carpet cleaners and other agents that might linger in the environment. Furnace and air-conditioning filters should be changed regularly, and air filter or humidifiers may be helpful in some cases. Follicular conjunctivitis usually responds to topical corticosteroids and the disease usually subsides as the dogs mature.
• Corneal ulcers are generally treated with topical antibiotics and possibly pupil dilators. Many corneal ulcers heal within three to five days.
• Allergy associated conjunctivitis is treated with topical antihistamines or topical steroids. This can alleviate some of the redness and inflammation. Removal of the item your dog is allergic to can also help eliminate the disease, but frequently this is not possible.
• Inflammation of the eyelids and cornea must also be addressed.
• Conjunctivitis associated with systemic illness in the dog often resolves as the dog’s primary problem is corrected and the dog starts feeling better.