What is conjunctivitis?
Conjunctivitis refers to inflammation of the conjunctiva tissue. The conjunctiva is a mucous membrane like the lining of the mouth and nose. This membrane covers the white part of 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 dogs, 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 clinical signs of conjunctivitis are 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 or canine herpesvirus.
- Bacterial infections such as Staphylococci; may be primary or secondary.
- Immune-mediated disorders such as allergic conjunctivitis (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 (turning in of the eyelids), ectropion (turning out of the eyelids), and eyelash disorders such as distichiasis and ectopic cilia often cause secondary conjunctivitis due to irritation from hairs rubbing on the eye.
- Obstructed tear ducts can cause inflammation of the tissues surrounding the globe of the eye.
- Other eye disorders such as corneal ulcers, anterior uveitis (inflammation inside the eye), and glaucoma (high pressures inside the eye).
- Trauma to the eye or irritation from foreign bodies, smoke, or environmental pollutants.
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 or eyelids, it may be a secondary problem. To differentiate many of these conditions, a complete and detailed ophthalmic examination must be performed by your veterinarian, often using an ophthalmoscope. This will include detailed examination of the eye and surrounding structures (eyelids, eyelashes, tear ducts, third eyelid, etc.).
Specific tests may be performed based on the examination and history.
- Your veterinarian may measure tear production (Schirmer tear test).
- Your veterinarian may measure intraocular pressure to rule out glaucoma or uveitis.
- The cornea may be stained with fluorescein dye to look for underlying corneal injuries or ulcers.
- 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. Topical, antibiotic eye ointments or drops are commonly prescribed. Some dogs will receive medication containing anti-inflammatory agents such as topical steroids. Allergic conjunctivitis may be improved by identifying and eliminating allergic triggers if possible (e.g., environmental irritants such as cigarette smoke, dust, and harsh chemicals).
In dogs that have secondary conjunctivitis, treatment will be directed to the primary problem. Dogs diagnosed with KCS usually require medications such as cyclosporine or tacrolimus to stimulate tear-production, as well as lubricants. Dogs with eyelid or eyelash abnormalities will require surgical correction. Dogs with corneal ulcers, glaucoma, or uveitis often require multiple different eye and oral medications.
Will my dog recover from conjunctivitis?
Most cases of conjunctivitis have a very good prognosis. Severe, chronic, or recurrent conjunctivitis may have a guarded prognosis, depending on the diagnosis. Conditions such as KCS and immune-mediated disorders may require lifelong therapy. If a surgical condition is identified and treated, prognosis is excellent; however, if surgery is not pursued, then long-term complications can occur.