Follicular conjunctivitis in a dog

Photo by Dr. Andrea Weidner

Conjunctivitis is inflammation of the conjunctiva in the eye. The conjunctiva is a pinkish mucous-secreting membrane, similar to the lining of your mouth and nose, that covers the eyeball and lines the inner surface of the eyelids. The conjunctiva also covers the third eyelid, or nictitating membrane, that dogs and cats have but you do not. Inflammation, as indicated by the suffix ‘-itis’, is tissue that is red, warm, swollen, and usually painful as a result of disease or injury.  

In conjunctivitis those membranes become red and swollen. Dogs and cats with conjunctivitis normally have cloudy, yellow, or greenish discharge from the eyes; a lot of blinking or squinting; and redness and swelling around the eye. Green or yellow discharge often indicates a bacterial infection; clear or whitish discharge is more likely to be caused by allergies or a bit of debris in the eye. Usually both eyes are affected, but not always. Sometimes other signs are seen, such as itching, hairlessness around the eye, discharge from the nose, sneezing, or coughing.

What we normally call “pink eye” in people is a type of conjunctivitis. The condition can be caused by several reasons, such as bacteria, herpes virus or allergies.

Any breed of dog or cat may develop allergic conjunctivitis. All breeds predisposed to atopic dermatitis, a hypersensitivity or over-reaction to a variety of commonplace and otherwise harmless substances like pollen, are also predisposed to allergic conjunctivitis. Allergic conjunctivitis is most common in young adults but can occur at any age.

In this allergic condition, the following are frequent contributors:

• Allergies
• Atopy (genetic tendency towards allergies)
• Dust
• Food allergy
• House dust, molds

Treatment

Allergic conjunctivitis is most commonly treated with eyedrops or ointments containing corticosteroids, such as dexamethasone or hydrocortisone. Your veterinarian may check first for a scratch on the cornea (called a corneal ulcer) by instilling a yellow dye called fluorescein. If the eye has a scratch, medication without steroids is used, as steroids can delay healing of the scratch. Oral corticosteroids and/or antihistamines may also be helpful, especially in those pets with associated skin disease. Over-the-counter topical antihistamines may be beneficial, particularly in itchy dogs, but ask your veterinarian which one is best for your pet’s situation. However, topical mast cell stabilizers and antihistamines have variable clinical results.

A sterile saline eye wash can be used once or twice a day to clean the eyes and remove the accumulated discharge. Saline may also reduce surface irritation by flushing dirt, dust, debris, and pollens away from the eye.

Preventing damage to the eye is important as pets with allergic conjunctivitis may scratch at their eye with their paws or rub their face on furniture. This rubbing can lead to a corneal ulcer and associated pain and damage to the eye. Using an Elizabethan collar to prevent scratching may be part of the treatment plan from your veterinarian. This is especially important in short-faced breeds like pugs and shih-tzus, who are particularly prone to eye injuries. A recheck examination may be recommended by your veterinarian after treatment. If signs have not improved, your veterinarian may suggest sending your pet to a veterinary dermatologist or ophthalmologist for a work-up or recommending allergen testing to try and determine what your pet is allergic to. This step is usually reserved for dogs or cats with severe allergies.

Prevention

Allergic conjunctivitis is caused by allergies, so the best way to prevent it from happening again is to remove whatever your pet is allergic to from your home, if possible. Even if you can figure out what allergen they are reacting to and remove it or deal with it, you may not be able to eliminate it. If dust is found to be a cause, keep household dust to a minimum, and consider using an air purifier to filter out dust.

Allergic skin testing or food trials may be needed to find out the cause of the inflammation. In those cases, you may be able to determine if your dog or cat is reacting to something like dust or an ingredient in their food.

In many cases, allergic conjunctivitis can’t be cured, but with the help of your veterinarian (and perhaps a few steps taken around the house) it can be managed and you can make your pet more comfortable.