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Conjunctivitis at a glance
About: Conjunctivitis is the inflammation of the conjunctiva, which is the membrane covering the front of the eyeball.
Causes: There are a number of causes including infection, allergies, irritants, injury and foreign object in the eye.
Treatment: This depends on the underlying cause but may include antibiotics, anti-virals, and removal of the discharge.
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. It 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 as failure to do so could result in loss of vision.
The cause may be 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, kittens and cats in overcrowded environments such as shelters are most commonly affected.
- Calicivirus is another common upper respiratory infection which is most often seen in kittens, overcrowded environments or immunocompromised cats. FHV-1 and Calicivirus are responsible for 80-90% of upper respiratory infections in cats.
- Feline Chlamydophila is a bacterial infection characterised by mind rhinitis, fever, localised lymph node swelling and ocular discharge.
- Mycoplasma is 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).
- Injury (scratch).
- 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.
- Eye tumours.
- 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 is 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 and obtain a history from you. You may be asked the following questions:
- Your cat’s vaccination history.
- How have long symptoms been present?
- What other symptoms has your cat had?
Diagnostic tests may include:
- Conjunctival swab – A swab from the affected eye 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 – 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. Determining the causative agent where possible.
- Purulent conjunctivitis requires eye irrigations and warm saline soaks to loosen crusted eyelids.
- Antibiotic eye ointment (usually topical tetracyclines) applied several times a day to treat bacterial infections.
- Systemic antibiotics if your cat has Chlamydophila, recent research has revealed the pathogen may hide away in non-ocular sites.
- Antiviral eye medications.
- Antibiotics to treat secondary bacterial infections which can develop in cats with viral conjunctivitis.
- L-Lysine to suppress viral replication of the herpes virus.
- Other treatments for cats with chronic FHV-1 conjunctivitis may include topical or systemic interferon and systemic anti-virals such as aciclovir.
- Removal of the allergen where possible and anti-inflammatories to treat allergies.
- 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 to keep eyes moist for cats with dry eye.
- Cyclosporine is an immune modulating medication that can help suppress immune system inflammation of the tear glands.
- Entropion may require corrective surgery.
Once a cat has herpesvirus he has it for life. After an outbreak, the virus will lie dormant and may be shed intermittently, especially during times of stress or sickness.
Keep cats as stress-free as possible.
Isolate cats who have conjunctivitis due to infectious causes to avoid spreading the infection.
- Remove discharge from the eyes with a cotton ball gently soaked in warm water.
- Administer all medications as prescribed by your veterinarian and always complete the course.
- Wash hands with warm soapy water before and after handling a cat with conjunctivitis.
- Keep your cat indoors while he is receiving treatment.
There are routine vaccinations available for FHV-1, Calicivirus and Feline Chlamydophila.
Image courtesy of Nottingham Vet School