Conjunctivitis, sometimes called red eye or pink eye, is an inflammation of the conjunctival membrane that covers the back of the eyelids and the surface of the eyeball, up to the cornea. It is one of the most common eye problems in dogs.
The classic signs of conjunctivitis are a red eye with a discharge. Conjunctivitis is not usually painful. If the eye is red and the dog is squinting and shutting the eye, consider the possibility of keratitis, uveitis, or glaucoma. Any delay in treating these conditions can lead to blindness.
When the discharge involves both eyes, suspect an allergy or a systemic disease such as canine distemper. When it involves only one eye, consider a local predisposing cause such as a foreign body in the eye or hair rubbing on the eye.
The eye discharge in conjunctivitis may be clear (serous), mucuslike (mucoid), or puslike (purulent). A stringy, mucoid discharge suggests the dog may have inadequate tear volume, a problem associated with keratoconjunctivitis sicca. In fact, this is the most common cause of conjunctivitis in dogs.
Serous conjunctivitis is a mild condition in which the membranes look pink and somewhat swollen. The discharge is clear and watery. Serous conjunctivitis is caused by physical irritants such as wind, cold, dust, and various allergens such as those that cause allergic blepharitis. Allergic conjunctivitis is often accompanied by itching, and the dog will rub his face. Some viral agents will cause a clear discharge as well.
Follicular (mucoid) conjunctivitis is a condition in which the small mucous glands (follicles) on the underside of the nictitating membrane react to an eye irritant or infection by forming a rough, cobblestone surface that irritates the eye and produces a mucoid discharge. After the inciting factor has been treated, the follicles may persist and the rough surface acts as a chronic irritant.
Purulent conjunctivitis is serous conjunctivitis that becomes infected. The usual culprits are the bacteria Streptococcus and Staphylococcus. The conjunctiva is red and swollen. The eye discharge contains mucus and pus. Thick secretions may crust the eyelids.
Treatment: Any underlying cause of conjunctivitis should be corrected. Dogs with recurrent or persistent conjunctivitis should be tested for keratoconjunctivitis sicca.
Serous conjunctivitis can be treated at home. Flush the eye three or four times a day with an over-the-counter sterile saline eyewash or artificial tears. Notify your veterinarian if the eye appears to be getting worse.
Mild cases of follicular conjunctivitis respond to antibiotic and corticosteroid eye ointments prescribed by your veterinarian. In resistant cases, the follicles may need to be destroyed by chemical cauterization.
Purulent conjunctivitis requires veterinary examination and treatment. It is important to remove mucus and pus from the eyes, as well as pus and crusts that adhere to the eyelids. Moisten a cotton ball with sterile eyewash and gently cleanse the eye. Warm, moist packs may help loosen crusts. Repeat as necessary and apply topical antibiotics as prescribed by your veterinarian (see How to Apply Eye Medicines). Continue topical antibiotics for several days beyond apparent cure.
Note that corticosteroids and eye medications containing corticosteroids should not be used in dogs with purulent conjunctivitis because they impair the local inflammatory response that fights infection. Bacterial culture and sensitivity tests are indicated if the conjunctivitis does not improve.