The most common infections of that can cause this are Feline Herpes-1 virus (rhinotracheitis virus) and infection with Chlamydia psittaci or mycoplasma.

When these organisms first infect cats they result in generalized upper respiratory infections with fever, weepy eyes, crusty nose and sneezing (see article: Respiratory Infections In Your Cat). These infections clear up after a few weeks with or without treatment, and most cats are never again bothered with the problem.

But a small percentage of cats that become infected with Herpes virus 1, become chronic carriers of the virus and relapse from time. In most cats, these relapses are limited to nasal drainage or sinusitis. In some, relapses occur in the eyes with periodic drainage, inflammation and the formation of rounded milk white corneal scars. The condition is then called Infectious Feline Keratoconjunctivitis.

Between episodes, this virus resides in the nerves of the face. Corneal scars range in size from pinpoint to over a centimeter in diameter are common. Herpes-1 of cats is similar to herpes simplex, the causes of fever sores in humans. However, do not worry, the herpes virus of cats can not infect you. Both these viruses live in the nerves and relapse during periods of stress. During relapse cats tend to hold their eye(s) partially shut.

Usually flare-ups are associated with the stress of boarding, weather change, other disease or new cats in the family or neighborhood. During this period the outer coating of the cornea is lost to the invading virus. Secondary bacterial and mycoplasmal infection of these areas can lead to deep ulcers of the cornea and occasionally to eye-threatening penetration of the eye itself. Deep ulcers need immediate veterinary care.

Can Other Problems Be Confused With Viral Or Bacterial Eye Infections?

There are non-infectious conditions that mimic this disease. These include allergic and eosinophilic conjunctivitis and sensitivity to eye medications, environmental irritants and trauma. Cats rub eyes that itch for any reason and the result can be corneal tears and scrapes.

Diseases that increased ocular pressure (glaucoma) and inflammation of the forward chamber of the eye (uveitis) can also cause damage and scaring of the cornea. Persian cats are susceptible to dry eyes, which can also cause corneal ulcers.

What Treatment Is Available?

Diagnosis of Herpes-1 eye infection based on gross examination of the eye is difficult. We often do so only by ruling out other causes. So we often medicate these eyes with a number of agents that are effective against secondary invaders like mycoplasma and chlamydia but not against Herpes-1.

The amino acid, l-lysine, has been found to help many cases of rhinotracheitis resolve. This amino acid reduces the amount of another amino acid, arginine, that is present in the cat's body. Arginine is thought to be necessary for herpesvirus to reproduce. The suggested lysine dose is 250-500 mg per day sprinkled on canned cat food. I would give this supplement until the acute flare-up has resolved. But many cat owners continue the supplement indefinitely. Lysine can be purchased at health food stores. Pick a brand that is propylene glycol-free.

Eosinophilic keratitis (corneal inflammation) is diagnosed by staining a preparation of corneal cells. Treatment of that condition utilizes corticosteroid eye drops. Eye irritation due to environmental contaminants and allergies also respond well to corticosteroids. But if steroids are given to Herpes-1 carrier cats the problem can actually get worse.

Dry eyes are diagnosed with the Schirmer tear test, a test that gauges the amount of tears that are produced.

Cats that are squinting should have their eyes stained with fluorescein dye. This allows us to see early corneal ulcers and gauge their depth. Deep ulcers sometimes need a temporary emergency corneal patch. I have found that Herpes-1 cats respond better to simple T.L.C. than to all the medications I can dispense. Since I am never one hundred percent certain which agents are involved I put all these cats on Tetracycline (Terramycin) or chloramphenicol ophthalmic ointment. Although this does not affect the virus, it does eliminate secondary bacterial infections. If the condition does not begin to resolve within two weeks, I place the cats on trifluorothymidine (Viroptic) eye drops or Trifluridine eye ointment. Because both these products can irritate the eye I give the body’s own immune system time to eliminate the virus on its own before resorting to these medications Chicken soup is an excellent first-line treatment for Herpes-1 virus. It can be fed through a dropper if need be to prevent dehydration and tempt depressed cats and those with eye problems into eating. Sometimes pungent foods like sardines and tuna will be accepted when all else fails.

How Can I Prevent This Problem?

A portion of the cats that have this problem test positive for feline leukemia or feline immunodeficiency virus. When these have been ruled out, lowering the stresses in a cats life is the best preventative. Some of these cats do much better in a single cat family. Diets rich in vitamin A may also decrease the frequency and severity of relapses. Good vaccines are available to prevent this disease. I give them to kittens at 9, 12 and 14 weeks of age. The problem is that many kittens are already infected with herpes-1 virus before they leave their mothers and come to see me. The stress of pregnancy, and more so nursing, causes these carrier mothers to relapse and infect their kittens. Many cats from shelters are in the middle of a relapse infection when I first see them. In these instances the vaccines will not work. Until recently, vaccinations were given yearly to cats in the United States. There is evidence that rhinotracheitis and Calicivirus vaccines do not need to be given that frequently. When they are given they should be administered through 25-guage needles on the anterior side of a rear leg and the injection site should then be vigorously massaged. This may decrease the very rare instances where tumors forms at injection sites in cats.

Recently, it was found that a large number of cats with eye problems were positive for Bartonella. Bartonella responded well to treatment with doxycycline, azithromycin or rifampin antibiotics. When using capsules or tablets you should follow the pill or with a considerable amount of water to keep it from lodging in your pet's throat.

Within the last few years,veterinarians have been given a tremendous tool for sorting out the various organisms that can cause chronic eye problem in your cat.(ref) Sophisticated central laboratory services are now available throughout the United States to do this. All utilize a very sensitive test, the Polymerase Chain Reaction or PCR test to look for six of the most common causes of upper respiratory and/or chronic eye problems in cats( Bordetella, Chlamydia, calicivirus, Herpes 1,influenza and mycoplasma). If your kitty has a persistent eye problem, some of these organisms are not the likely cause; but the panel tests for all of them. Its limitation is that the most common cause, the Herpes-1 (rhinotracheitis virus) is so stealthy that it can avoid detection with the PCR test when the cat is not experiencing a virus flare-up. So if the PCR test is positive for herpes-1, your cat is definitely a carrier of the virus. But if it is negative, the virus might still be sleeping somewhere deep in the cat's nerve cells. So if the test found no likely cause of your cat's chronic eye problem, it should be repeated at a later date - preferably during a flare-up.

Two of the laboratories offering this panel are Idexx Laboratories and Zoologix Laboratories. You can read their test descriptions through the company name links I provided.