Also known as “pinkeye“, conjunctivitis is a common disease in cats characterised by inflammation and pinkness of the conjunctiva (the pink membrane which covers the front of the eyeball and the inside of the eyelids). Conjunctivitis can affect one eye (unilateral) or both eyes (bilateral) and covers a broad range of possible conditions. Conjunctival inflammation can be acute or chronic, infectious or non-infectious. It is extremely important to seek veterinary care when it comes to eye conditions. Failure to do so could result in loss of vision.
There are many possible causes of conjunctivitis in cats which can loosely be divided into infectious or non-infectious. The most common causes of conjunctivitis in cats are FHV-1, Calicivirus and Feline Chlamydophilia. All of which produce flu-like symptoms.
Feline herpesvirus (FHV-1) is an acute upper respiratory tract infection. It is seen most often in kittens and overcrowded environments such as shelters.
Calicivirus is another common upper respiratory infection which is most often seen in kittens, overcrowded environments or immunocompromised cats. Between 80-90% of upper respiratory infections are caused by FHV-1 or Calicivirus.
Feline Chlamydophila is a bacterial infection characterised by mind rhinitis, fever, localised lymph node swelling and ocular discharge.
Mycoplasma are an unusual class of bacteria which lack cell walls.
Bartonella is the bacteria responsible for cat scratch disease in cats. Infected cats generally have mild and self-limiting symptoms including fever, swollen lymph nodes, uveitis and conjunctivitis.
Most bacterial infections occur secondary to viral infections when irritation or damage to the sensitive tissues of the eyes expose them to opportunistic bacterial infections, common pathogens include Streptococci and Staphylococci.
Allergies (plants, pollens etc).
Blepharitis is an inflammation of the eyelid, which causes swelling and discomfort. Swelling can lead to irritation of the underlying conjunctiva.
Foreign object (grass seed, hair, sand, eyelash).
Irritants (eg; smoke, fumes, dust).
Entropion is a condition in which the eyelids fold inwards, this causes the eyelashes to rub against the eye, which causes irritation. Persians and Exotics are particularly at risk of this.
Keratoconjunctivitis sicca (KCS/dry eye) – This is an inflammation of both the cornea and the conjunctiva and sicca means dry. This is caused by a lack of tears reaching the surface of the eyes which is caused by trauma, inflammation of the conjunctival glands and ducts, scarring etc. 
Keratitis is an inflammation of the cornea, there are a number of causes including infectious and non-infectious. It is possible for inflammation to progress to the conjunctiva.
The most common symptoms of conjunctivitis in cats are eye discharge along with a meaty like appearance to the eye (as you can see in the image above).
Ocular (eye) discharge. This will vary depending on the cause of conjunctivitis. It may either be clear and watery or thick, containing mucus or pus. Thick and purulent discharge are more often due to bacterial infection (primary or secondary), watery discharge is more likely to be due to allergy or irritants.
The conjunctiva becomes red and swollen.
Pawing and rubbing at the eye.
Third eye protrusion.
Ulceration of the eye may also occur in cats infected with FHV-1.
This is a mild condition in which the conjunctiva looks pink and swollen. Discharge is clear and watery. Common causes include the wind, dust and allergens.
This often starts out as serous conjunctivitis which becomes purulent. Thick secretions crust the lids and the discharge contains mucus or pus. Bacterial infections are often the cause
Other symptoms may also be present depending on the underlying disease. The most common causes of conjunctivitis are feline herpes virus and chlamydopilia, both of which typically produce flu-like symptoms such as fever, nasal discharge, and sneezing along with conjunctivitis.
Cats with chlamydophilia may develop conjunctivitis in one eye which then progresses to the second eye a few days later.
Your veterinarian will perform a physical examination including looking closely at the eyes and type of discharge (watery, thick etc.) and obtain a history from you including how long your cat’s eye(s) have been like this, his vaccination history, other symptoms you may have noticed. He may be able to diagnose the cause based on signs and symptoms.
He may wish to perform some tests including:
Thorough examination of your cat’s eye to look for foreign body.
Conjunctival swab – Your veterinarian may take an eye swab from an infected cat which will be sent to a laboratory for testing. There are several tests which can be performed, including PCR (polymerase chain reaction), Immunofluorescent assay (IFA) or bacterial culture.
Fluorescein staining – This is a dye which is used to stain and demonstrate ulcerations of the cornea.
Treatment depends on the cause of conjunctivitis. Mild cases of conjunctivitis may only require flushing of the eye with a saline solution. Ideally the causative agent will have been determined.
Purulent conjunctivitis requires eye irrigations and warm saline soaks to loosen crusted eyelids.
Antibiotic eye ointment (usually topical tetracyclins) applied several times a day to treat bacterial infections.
Systemic antibiotics may also be prescribed if your cat has Chlamydophila as recent research has revealed the pathogen may hide away in non-ocular sites.
Antiviral eye medications for viral conjunctivitis. Even if the cause is viral, your veterinarian may prescribe broad spectrum antibiotics to treat or prevent secondary bacterial infections.
L-Lysine has been shown to suppress viral replication and inhibit cytopathogenicity for cats with feline herpes.
Other treatments for cats with chronic FHV-1 conjunctivitis may include topical or systemic interferon and systemic anti-virals such as aciclovor.
If allergy is the cause, anti-inflammatories may be prescribed as well as removal of the allergen if possible.
If a foreign object is the cause, removal should solve the problem. This usually involves irrigating the eye with a saline solution to dislodge the object.
Artificial tears will be used to keep eyes moist for cats with dry eye along with Cyclosporine which is an immune modulating medication which can help suppress immune system inflammation of the tear glands.
Surgery may be required to correct entropion.
Once a cat has herpesvirus he has it for life. After an outbreak it will lie dormant and be shed intermittently. Shedding is precipitated by stress, and as such, the cat should be kept as stress free as possible. Cats who have conjunctivitis due to infectious causes should be isolated from other cats until they have recovered to avoid spreading the infection.