Conjunctivitis (Pinkeye) in Cats

Conjunctivitis is an inflammation of the membrane covering the back of the eyelids and surface of the eyeball up to the cornea. It is one of the most common eye problems in cats. Conjunctivitis in cats almost always has an underlying infectious cause. The most common cause is the herpesvirus (FHV-1), and the second most common is chlamydophila. 

Signs:

• red eye
• discharge 
• pawing at the eye to relieve itching
• The conjunctival tissues may be red and swollen. 

Untreated conjunctivitis may progress to vision-threatening problems. Conjunctivitis is not painful-although it is itchy. If the eye is red, irritated, and painful to touch, consider the possibility of keratitis, uveitis, or glaucoma. Delay in treating these conditions could result in loss of vision.

Serous Conjunctivitis

This is a mild condition in which the membrane looks pink and somewhat swollen. The discharge is clear and watery and is caused by physical irritants such as wind, cold weather, dust, or various allergens. This condition must be distinguished from a tearing problem.

Serous conjunctivitis may be the first sign of a feline viral respiratory disease or a chlamydophila infection. Eye worms are a rare cause of conjunctivitis.

Treatment: Mild, irritating forms of conjunctivitis can be treated at home. The eye should be cleansed with a dilute solution of boric acid for ophthalmic use, artificial tears, or a sterile ophthalmic irrigating solution that can be purchased over the counter and used as directed for people. You should see definite improvement within 24 hours. If not, bring your cat to the veterinarian.

Purulent Conjunctivitis

Purulent conjunctivitis begins as serous conjunctivitis that becomes purulent. Thick secretions crust the eyelids. The eye discharge contains mucus or pus. This suggests secondary bacterial infection.

When the discharge involves both eyes simultaneously, suspect a virus. This could be herpesvirus or calicivirus. When it involves one eye at first and progresses to the other eye several days later, suspect chlamydophila or mycoplasma. These microorganisms can be detected under a microscope by your veterinarian, in scrapings taken from the conjunctival membrane. Ulcers on the cornea are diagnostic for herpesvirus conjunctivitis.

Conjunctivitis due to fungal infection is rare and requires special laboratory aid for diagnosis.

Treatment: Purulent conjunctivitis requires eye irrigations and sometimes warm soaks to loosen crusted eyelids. Antibiotics are applied to the eye surface several times a day. They should be continued for seven days beyond apparent cure. An ointment containing a combination of neomycin, bacitracin, and polymyxin (such as Neosporin ophthalmic ointment) often works well.

If the condition is caused by chlamydophila or mycoplasma, eyedrops containing tetracycline or chloramphenicol are the antibiotics of choice. Chlamydophila conjunctivitis can result from cats shedding organisms in their stool or urine after the infection appears to be cleared. This carrier state can be treated by your veterinarian with a three-week course of doxycycline or a week of azithromycin.

Deep-seated infections are difficult to clear up. In such cases, you should suspect involvement of the tear drainage system. Repeated cleansing of the eye, correction of any underlying problem, and specific topical and oral antibiotics tailored to cultures and sensitivities form the primary approach to this problem.

Antiviral eye medications are available for the treatment of viral conjunctivitis. They must be prescribed by a veterinarian. Cats with herpesvirus often have chronic recurrent conjunctivitis and may periodically be a source of infection for other cats. Research at Colorado State University is using a new antiviral drug, cidofovir, to treat cats with herpes conjunctivitis. This medication needs to be given twice a day and is not as irritating to the cat as other antiviral medications.

Follicular Conjunctivitis

This is a condition in which the small mucous glands (also called follicles) on the underside of the nictitating membrane form a rough, cobblestone surface that irritates the eye and produces a mucoid discharge. Various pollens, allergens, and infective agents are implicated as causes. After the initiating factor has been removed, these follicles may remain enlarged. The roughened surface of the conjunctiva then acts as a persistent irritant to the eye.

Treatment: A steroid-based eye ointment can be used to decrease the size of the follicles and smooth the surface. If steroids are not effective, your veterinarian can mechanically or chemically cauterize the follicles. Steroids should not be used unless an infectious cause has been ruled out.