Conjunctivitis is a general term for inflammation of the conjunctivae, the anatomic structures that constitute the fleshy mucous membrane-lined tissues surrounding the eyes.
Conjunctivitis is widely perceived by pet owners as akin to "pink eye" in humans and, as such, an infectious condition of bacterial origin. However, this is only rarely the case in dogs and cats.
In fact, bacterial conjunctival infections in dogs typically occur secondary to a condition known as "dry eye" (keratoconjunctivitis sicca or "KCS") or allergies. In cats, conjunctivitis usually originates as a virus, with the development of bacterial conjunctivitis only secondarily.
Conformational issues such as distichiasis (hair from the lids poking into the eyes), entropion (curling in of the eyelids), and ectropion (sagging of the eyelids) may also create conditions favorable to conjunctivitis. Indeed, any condition that leads to ocular irritation (including traumatic conditions and/or painful diseases of the cornea) can also lead to conjunctivitis.
Symptoms and Identification
Dogs and cats with conjunctivitis may show one or more of the following:
Redness of the eyes
Swelling of the conjunctivae and sometimes the eyelids
Rubbing or pawing at the eyes
Swelling of the mucous membranes
Excessive clear ocular discharge ("tearing")
Opaque ocular discharge (yellow to greenish is common)
The following tests are commonly undertaken as part of the diagnosis of conjunctivitis:
Fluorescein dye test (to assess corneal integrity)
Schirmer tear test (for dry eye diagnosis)
Culture and sensitivity of discharge
Cytology of conjunctival scraping
Breeds of dogs and cats predisposed to dry eye, allergies, or recurrent viral infections are genetically predisposed. Those who suffer from hereditary conformational issues are similarly overrepresented.
Administration of topical ophthalmic antibiotics is necessary in most cases of secondary bacterial conjunctivitis. Steroid-containing medications may also be deemed necessary. The type and frequency of the medications will correspond to the cause, severity, and complications of the disease process.
Identifying and treating the underlying condition, however, is fundamental to the long-term success of conjunctivitis treatment.
The cost of diagnosis and treatment of conjunctivitis is considered quite manageable by most pet owners. Treatment of the underlying conditions, however, may prove less affordable -- particularly should surgical solutions play a leading role.
Limiting the breeding of dogs and cats affected by heritable conditions that predispose them to conjunctivitis is the ideal means of prevention. In pets already affected by these conditions, treating the underlying disease processes that lead to conjunctivitis is the next best approach to its prevention.
Lourenco-Martins, A.M.; Delgado, E.; Neto, I.; Conceicao Peleteiro, M.; Morais-Almeida, M.; Duarte Correia, J.H. Allergic conjunctivitis and conjunctival provocation tests in atopic dogs. Veterinary Ophthalmology (July 2011), 14 (4), pg. 248-256
Hsuing, G.D.; Eads, F.E., Stafseth, H.J. Penicillin ointment in the treatment of conjunctivitis in dogs. Journal Cornell Veterinarian 1950 Vol. 40 pp. 4-10