Conjunctivitis in Cats

March 7, 2020

What is conjunctivitis?

The conjunctiva is a thin mucous membrane composed of epithelial and mucus-secreting cells that covers the anterior sclera and eyelids including the third eyelid located at the inner corner of the eye. In normal cats, the conjunctiva of the eyelids is not readily visible and has a pale, pink color. When inflamed (conjunctivitis), the conjunctival blood vessels dilate to become red (hyperemia) and swollen (chemosis).  Discharge can vary from watery (serous) to thick and clear (mucoid) to thick and yellow (purulent). Conjunctivitis can affect one (unilateral) or both (bilateral) eyes. Your cat may squint or keep its eyes closed, because of either discomfort or photophobia (a reluctance to be in bright light) or, in severe cases, the conjunctival tissue or the third eyelid may be so swollen that it may partially or fully cover the eye.

What are some causes of conjunctivitis?

The most common causes of conjunctivitis can be divided into two categories: infectious diseases and non-infectious conditions including allergies, hereditary conditions and tumors. Conjunctivitis in commonly a secondary sign of another eye disease including glaucoma, uveitis, corneal disease, and scleritis.

Infectious Causes of Conjunctivitis

Infectious agents such as bacteria, viruses, and fungi are the most common causes of conjunctivitis in cats. In many cases, viruses such as Feline Viral Rhinotracheitis (FVR), also known as feline herpesvirus (FHV-1) or Feline Calicivirus are the initial cause of inflammation. Primary viral infections are often complicated by secondary bacterial infections with a variety of bacteria including Streptococci and Staphylococci. Two additional organisms, Chlamydophila felis and Mycoplasma, are also capable of initiating primary conjunctivitis.

Non-infectious Causes of Conjunctivitis

Breeds such as Persians, Himalayans and other longhaired breeds may manifest with entropion which causes corneal irritation as the eyelashes constantly rub against the eyeball. Foreign bodies such as dust or sand may become trapped inside the eyelids, or exposure to irritant chemicals may initiate conjunctivitis that may become secondarily infected Allergies are believed to be a common cause of conjunctivitis, but the specific allergens can sometimes be difficult to identify or avoid. Conjunctivitis is a common symptom of eye tumors. Eosinophilic conjunctivitis is presumed immune-mediated and is discussed elsewhere as a separate topic. And, in certain geographic areas Thelazia spp. may be found in the fornix

How is conjunctivitis diagnosed?

A tentative diagnosis of conjunctivitis is made after your veterinarian rules out other conditions such as a foreign body in the eye, scleritis, obstructed or infected tear duct preventing normal drainage of tears, or a corneal ulcer or other injury to the eye.


Since secondary bacterial infections cause many of the symptoms, and because there is a need to reduce the immediate pain and inflammation, antimicrobial treatment is usually begun based on this tentative diagnosis of infectious conjunctivitis, Most bacterial and viral infections will resolve within five to fourteen days. In cases that are not improving or where there are other animals at risk, further testing may be performed to reach a definitive diagnosis.

Specific tests maybe performed, based on the medical history and results of an examination of the eye and surrounding tissues. Your veterinarian may measure the tear production and intraocular pressure (pressure within the eyes) for each eye. The cornea may be stained with fluorescein dye to look for underlying corneal injuries or ulcers, and conjunctival scrapings or biopsies may be obtained and sent to a diagnostic laboratory for specialized testing. The nasolacrimal or tear ducts may be flushed to ensure proper drainage. Blood tests will be performed to determine if the conjunctivitis is related to a systemic condition.

The general approach to non-specific conjunctivitis is to use ophthalmic preparations containing a combination of broad-spectrum antibiotics to control the secondary bacterial infection and anti-inflammatory drugs to reduce the inflammation. These preparations come as either drops or ointment for instilling into the eyes. Local treatment may need to be supplemented with injections and pills.

If a specific diagnosis has been reached, one of the following treatment regimens may be considered:

Herpesvirus conjunctivitis

Although these infections are usually mild and self-limiting, the infected cat remains a carrier of the virus, and may experience intermittent relapses.

  • Antiviral medications are used in severe or poorly responsive cases. FHV-1 is a systemic disease and is treated with oral famciclovir 40 mg/kg 2X daily X 2-3 wks.
  • L-lysine may be used to promote healing, and may be used for life as an immune-stimulant for cats that have recurrent problems
  • Antibiotics are often used if a secondary bacterial infection is present
  • Interferon-alpha may be used as an immune stimulant

Chlamydophila or mycoplasma conjunctivitis

  • Tetracycline ophthalmic ointment
  • Azithromycin oral antibiotic

Eosinophilic or Allergic conjunctivitis

  • Topical corticosteroid ointment or drops
  • Refractory cases or if animals are difficult to treat may be administered
  • oral anti-imflammatory medication
  • Topical medications to stop temper the allergic reaction

How do I administer eye medications?

Topical. Regular and frequent treatment is essential in successfully treating conjunctivitis. Most ophthalmic drops need to be administered three to six times a day at the start of treatment. Ointments may require less frequent administration, but may be more difficult to administer and more irritating to the patient. Two people may be necessary; one to hold the cat and the other to administer the eye medication, at least until the discomfort and sensitivity of the eyes has decreased. Apply 1/4 to 1/2 inch (0.6 to 1.25 cm) of ointment to each eye and then close the lids to smear the ointment across the eyeball.

Liquid preparations can be applied directly onto the surface of the eye; one or two drops per eye are usually sufficient. If you have any doubts as to how to give your cat’s medication, please ask us to demonstrate the proper procedure for you.

When should I expect a response?

Normally you will see a rapid improvement within a few days. However, even if the conjunctivitis has resolved, do not stop treatment until the end of the prescribed period. Stopping your cat’s medication early may allow a resurgence of the infection and make it harder to eliminate the next time.

What is the prognosis for a cat diagnosed with conjunctivitis?

The prognosis depends on the specific diagnosis. With some non-infectious causes, if the underlying cause is not removed the conjunctivitis will recur and long-term management, titred to effect, is required. Some of the viruses that cause infectious conjunctivitis are “incurable” and may persist in a quiescent form (called a carrier state), with flare-ups from time to time, especially during periods of stress or illness. The therapeutic goal for these patients is to minimize the frequency and severity of recurrences through optimum nutrition, appropriate vaccination against preventable causes of disease and medical management when indicated.