Conjunctivitis in Dogs

What is conjunctivitis?

Conjunctivitis refers to inflammation of this conjunctiva tissue. The conjunctiva is a mucous membrane, similar to the lining of the mouth and nose. This membrane, a layer of epithelial cells with mucus-secreting cells, covers the eyeball and lines the eyelids.

Dogs have a third eyelid, or nictitating membrane, in the inner corner of the eye, which is also covered by conjunctiva. In healthy dog, the conjunctiva of the eyelids is not readily visible and has a pale, pink color. When conjunctivitis occurs, the conjunctival membranes become red and swollen.  

What are the clinical signs associated with conjunctivitis?

The most common clinical signs of conjunctivitis include discharge from the eyes (cloudy, yellow, or greenish), squinting or excessive blinking, and redness or swelling around the eyes. Conjunctivitis often involves both eyes, but only one eye may be affected in certain conditions. Conjunctivitis may occur with other clinical signs such as nasal discharge, sneezing, or coughing.

What causes conjunctivitis?

Specific causes of conjunctivitis include:

• Viral infections such as canine distemper virus.

• Immune-mediated disorders such as allergic conjunctivitis (especially common in pets with inhalant or seasonal allergies), plasma cell conjunctivitis (especially German Shepherds), and pemphigus (an autoimmune skin disorder).

• Tumors of the eyelids and conjunctiva.

• Breed-associated conditions such as nodular episcleritis in Collies and Collie crosses.

• Tear film deficiency such as keratoconjunctivitis sicca (KCS or dry eye).

• Eyelid abnormalities such as entropion or ectropion and eyelash disorders such as distichiasis and ectopic cilia often cause secondary conjunctivitis.

• Obstructed nasolacrimal or tear ducts can cause inflammation of the tissues surrounding the globe of the eye.

• Trauma to the eye or irritation from foreign bodies, smoke, or environmental pollutants can cause inflammatory conjunctivitis.

• Other eye disorders such as ulcerative keratitis, anterior uveitis, and glaucoma.

How is conjunctivitis diagnosed?

The main goal of diagnosis is to determine if the conjunctivitis is a primary or secondary problem, if there is additional disease or damage to the eye, if the condition is allergic, or if it involves the tissues of the eye itself (sclera). In order to differentiate many of these conditions, a complete and detailed ophthalmic examination must be performed. This will include detailed examination of the surrounding eye structures (eyelids, eyelashes, tear ducts, third eyelid, etc.), tear production tests (Schirmer tear production test), corneal stain tests to ensure that the cornea is not damaged, and measurement of intraocular pressure to rule out glaucoma or uveitis.

Additional tests and procedures that may be performed include nasolacrimal duct flushing, bacterial culture and sensitivity tests, conjunctival cytology or biopsy, and allergy testing.

How is conjunctivitis treated?

Treatment is directed at the specific cause and may include both topical and oral medications. Some dogs will receive medications containing anti-inflammatory agents. In dogs that have secondary conjunctivitis, oral antibiotics or anti- inflammatory medications may also be used. Dogs diagnosed with KCS will usually require medications lifelong to replace tear production.

Will my dog recover from conjunctivitis?

Most dogs have an excellent prognosis in most cases of conjunctivitis. Severe, chronic, or recurrent conjunctivitis may have a guarded prognosis, depending on the definitive diagnosis. Conditions such as KCS and immune-mediated disorders may require lifelong therapy.