Conjunctivitis (cats)

Conjunctivitis is any inflammation of the conjunctiva (lining of the eyelids).
Signs of conjunctivitis include hyperaemia (red eye), mucopurulent ocular discharge (build up of infected matter), epiphora (weeping) and discomfort. The condition may involve one or both eyes.
The list of underlying causes is extensive.

Cats differ from dogs in that the main causes of conjunctivitis are viral, mycoplasma or chlamydial infection as opposed to bacterial infection.
Chlamydia infections usually start in one eye and then spread to the other eye within 10 days. Owners with multiple cats should assume that all cats within the house have become infected, even though only 1 may be showing signs. To confirm infection it is possible to perform a Polymerase Chain Reaction (PCR) test, which will need to be performed by a specialist laboratory. Treatment of chlamydia will require a drug called doxycycline for at least 3 weeks and all the cats within a house should be treated. Recurrences of infection are common and owners should be aware that chlamydia has a low zoonotic risk (humans can become infected).

The principle viral cause is the Feline Herpes Virus (FHV). Apart from the conjunctivitis FHV may also cause rhinitis (infection in the nose), sneezing, respiratory infection and blepharospasm (spasm of the eyelid). Drugs used to treat FHV infections include lysine and a combination of acyclovir and interferon. A definitive diagnosis of FHV is difficult because the virus lives inside nerves and therefore samples of the eye tissue may show nothing.

Mycoplasma infections can be diagnosed based on culture of a sample taken from the eye and are generally treated with tetracycline type antibiotics.

Trauma, toxic chemicals or soap will require an examination to assess the damage and then irrigation to flush the eye.

Foreign bodies such as grass seeds can become lodged inside the eyelids producing sudden severe inflammation.