The conjunctiva is a mucous membrane, similar to that of the mouth and nose, that surrounds the eyeball forming a seal with the inner surface of the eyelids. The third eyelid is also covered by conjunctiva. In normal cats the conjunctiva is not readily visible and has a pale, salmon pink colour. Conjunctivitis is an inflammation of this membrane which becomes swollen and reddened often making it more visible. Conjunctivitis can affect one (unilateral) or both (bilateral) eyes.
Cats with conjunctivitis tend to have a discharge from their eye(s) which can be clear or thick and purulent. The conjunctiva is often more visible and reddened particular in the corner of the eye and can be swollen, partially covering the eye. Frequently the eye(s) are held half closed and the third eyelid is more prominent.
A number of different conditions will cause conjunctivitis, many are sudden in onset and easily treatable others cause a more chronic disease which can be more difficult to control.
- Mechanical and chemical irritants, trauma (e.g. cat fights) and foreign bodies tend to cause sudden onset (acute) conjunctivitis. In most cases treatment is rapidly effective once the exciting cause has been removed.
- Immune based diseases including some allergies can cause conjunctivitis. These diseases are rare in cats but can be difficult to treat, sometimes management of the symptoms is the only realistic option.
- The most common causes of conjunctivitis in cats are infectious agents these can be viruses (usually feline herpes virus type 1 – one of the cat flu viruses), bacteria (most commonly Chlamydia) and mycoplasmas (a group of organisms somewhat like bacteria).
In many cases, conjunctivitis will respond to topical symptomatic therapy using drops or ointment containing antibiotics. Other cases however, conjunctivitis do not respond well to topical therapy or appear to improve and then gets worse again once treatment has ceased. In such cases your veterinary surgeon may feel that a specific diagnosis is required. If the cause of the conjunctivitis is not infectious then a sample of cells from the conjunctiva can be helpful. A small number of cells are obtained by scraping the conjunctival surface with a cotton wool swab or spatula. If a larger sample is required then a surgical biopsy may be necessary. Special tests for Chlamydia can then be performed.
There are three options for treatment:
- Local administration using drops or ointments
- Local administration by injection under the conjunctiva – this technique is used in cats that are difficult to treat (e.g. feral cats) or would require very frequent administration of the drops/ointment
- Systemic treatment given by injection or by mouth is required to effectively treat some diseases e.g. Chlamydiosis, mycoplasmosis.
Regular treatment is essential, most ointments need to be administered at least twice a day, drops need to be given more frequently and so are less practical. Unfortunately, some treatments cause transient discomfort after administration, meaning two people are required, one to hold the cat and the other to give the treatment. Liquid preparations can be applied directly onto the surface of the eye, 1 or 2 drops per eye is usually sufficient. Ointment is applied across the surface of the eye, about half an inch per eye. The eyelids are then closed to spread the ointment over the entire surface of the eye. Generally ointments need to be given less frequently than drops as they persist for longer but some people find drops easier to administer. If you have any doubts as to how to give the medication prescribed then don’t be afraid to ask your veterinary surgeon or practice nurse to give a demonstration.
Discharges from the eyes are more common in long haired cats due to eyes being prominent and less well protected by the eye socket or abnormalities in tear drainage causing an overflow of tears.