The conjunctiva is the moist membrane that surrounds the eyeball and lines the inside of the eyelids. The third eyelid is also covered by conjunctiva.
Conjunctivitis is inflammation of this membrane, which becomes swollen and reddened. One or both eyes may be affected. Cats with conjunctivitis tend to have ocular discharge, which can be clear or purulent (yellow). Frequently, the eye(s) are held half-closed and the third eyelid is more prominent.
WHAT CAUSES CONJUNCTIVITIS?
There are many causes of conjunctivitis. In cats, infectious agents are the most common cause – viruses (usually Feline Herpes Virus 1, which is one of the “cat flu” viruses), bacteria (most commonly Chlamydia) and Mycoplasma (organisms which are similar to bacteria). Trauma eg. cat fights, chemical irritation eg. shampoos and foreign bodies eg. grass seeds will cause acute conjunctivitis. Allergies and other immune-mediated diseases will occasionally cause conjunctivitis in cats.
HOW IS CONJUNCTIVITIS DIAGNOSED?
Conjunctivitis is usually diagnosed on the basis of the clinical signs. However, if the condition does not respond well to treatment, or is recurrent, further tests may be recommended. Swabs for culture, scrapings for examination of conjunctival cells or surgical biopsies for tissue examination may be taken.
HOW IS CONJUNCTIVITIS TREATED?
Treatment usually involves application of drops or ointment to the eyes. Most ointments need to be applied at least three times daily and drops usually even more frequently. Unfortunately, some medications cause transient discomfort after application, so cats rapidly learn to try to avoid treatment. Usually two people will be needed, one to hold the cat and one to apply the medication. The eyelids must be open and the drops or ointment applied to the eye itself, not just to the outside of the eyelids. (Please ask your veterinary surgeon or nurse to show you if you are uncertain).
Sometimes systemic treatment, by oral or injectable medications, is necessary, for example, for treatment of conjunctivitis caused by Chlamydia or Mycoplasma.