It is quite common for cats to have eye irritation and eye mattering that comes and goes. In between those relapses, nothing more might persists than pinpoint or rounded milky-colored corneal scars – like my orange tabby cat on the top right. Do you see the two (. .) on the eye on the left?

Another cat’s scratch, a dusty environment, allergies, dry eyes, tear duct blockages, internal eye problems or an unhealthy amount of weight loss can all cause eye discharges or inflammation that looks quite similar. But more commonly it is due to persistent infections with microscopic organisms that irritate the clear surface of your cat’s eye (=its cornea = keratitis). The most common organism that causes that in cats is the Feline Herpes-1 virus (aka rhinotracheitis virus , cat flu). The second most common cause is probably infection with  Chlamydophila felis (aka Chlamydia felis), then Mycoplasma or a combination of two or more of any of them.

When these organisms infect your cat for the first time, they usually result in a generalized upper respiratory infections, perhaps with fever, weepy eyes, a crusty nose and sneezing (see Respiratory Infections In Your Cat). These infections usually clear up after a week or two with or without treatment. Most cats are never again bothered with the problem. But when your cat’s initial infection included the cat herpes-1 virus (a distant cousin of the human fever sore virus and chicken pox virus the virus never really leaves your cat’s body. A few virus live on in a dormant sleeping state in cells within your cat’s facial nerves  and perhaps elsewhere. We really do not know. In most cases, your cat’s anti-herpes antibodies persist and keep these dormant virus in check (from proliferating). But stress and other factors that weaken your cat’s immune system can allow the virus to awaken from its latency.

So a small percentage of cats that become infected with Herpes-1 virus relapse from time. In most cats, these relapses are limited to some nasal drainage, sinusitis or sneezing. Other cats (probably the majority) simple begin shedding the virus again without evidence of illness. But in some, virus relapses occur in the clear, superficial layers of your cat’s eyes (their corneas) with periodic drainage, inflammation and the formation of rounded milk white corneal scars- similar to the ones in the orange cat at the top of this article. Some vets call this condition Herpesvirus keratoconjunctivitis or Infectious feline keratoconjunctivitis.

You might wonder why this virus has an affinity for your cat’s eyes. It probably has to do with the unique characteristics of the tissue that makes up your cat’s cornea. To maintain transparency, your cat’s corneas have no blood vessels. Unlike other tissue, they receive their nutrients and antibodies only through the tears that bath them externally and blood elements that diffuse to them from deeper eye structures. To survive, corneal cells also rely on neurotropins supplied by the trigeminal nerves I already mentioned. 

Between episodes, corneal scars range in size from pinpoint and barely noticeable to over a centimeter in diameter. Although Herpes-1 of cats is in the same large herpes group of virus as the human herpes simplex virus, do not worry, the herpes virus of cats cannot infect you (or your dog) nor can human herpes virus infect them. (read here)   Even oysters have their own unique herpes issues. (read here)

Herpes virus flare-ups in cats are often associated with the stress of boarding, weather change, other disease issues that weaken immunity, new cats added to the family or new neighborhood cat rivalries. Adoption to a new home is a particularly stressful time for cats. During these virus-activation periods, portions of the outer coating of your cat’s cornea can be lost to the invading virus. Secondary bacterial and mycoplasmal infection of those vulnerable areas can lead to deep ulcers of the cornea if they are not tended to by your veterinarian. Occasionally they lead to sight-threatening penetration into the eye itself. That is another reason why deep corneal ulcers need immediate veterinary care.

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

Yes

As I mentioned, there are non-infectious conditions that can mimic this disease. These include allergic and eosinophilic eye disease (read more about that further down this page), sensitivity to eye medications, environmental irritants or traumatic eye injuries (cats rub eyes that are itchy for any reason and the result can be corneal tears and scrapes; sharp claws occasionally tear the cornea during cat fights). Misplaced eyelashes (distichiasis) can also be a cause. (read here)

Diseases that increase your cat’s intra-ocular (eye) pressure (= glaucoma) and inflammation of the forward (anterior) chamber of your cat’s eye (uveitis) can also cause damage and scaring of its cornea. Due to their head conformation, Persian cats are more susceptible to dry eyes. That can also result in corneal ulcers.

What Treatments Are Available For My Cat?

Your veterinarian’s visual inspection of your cat’s eyes can’t be 100% certain in diagnosing a corneal herpes-1 virus problem. But your veterinarian knows  that there are very few other common explanations for the distinctive scars this virus often leaves behind. So your vet might add some other tests (such as fluorescein dye examination, swab cultures and cytology) to help rule out other causes or cases that might have multiple causes. PCR tests for feline herpes virus do exist. ( see here: ) However with so many cats shedding this virus, one cannot be certain that the herpes virus is the underlying cause of your cat’s eye issues even when the test results are positive. When multiple pathogens are detected or suspected, your veterinarian might add antibiotics or anti-fungal agents to the treatment plan. Antibiotics and antifungal medications are effective against secondary invaders like mycoplasma, chlamydia and yeast, but not specifically against Herpes-1. When that is not the case, most cats get better when their stress levels are reduced. When the viral relapses linger or when large portions of your cat’s cornea are involved, the most effective treatment is famciclovir (Famvir®). Read more about that medication here. Older, less expensive, topicals like idoxuridine eye drops (Herplex®) might also be effective – but you have to give them frequently throughout the day and side effects are unpredictable. (read here  &  here) If you work schedule or hesitancy prevents that, 0.5% custom-compounded cidofovir eye drops given twice a day might be effective as well. ( read here )

For many years, the amino acid, lysine, administered orally twice a day, was thought to help cases of Herpes-1/rhinotracheitis in cats to resolve and perhaps to even decrease the frequency of relapses. This amino acid was thought to reduce the amount of another amino acid, arginine, that is present in the cat’s body (although experiments to document that had mixed results). Arginine is thought to be necessary for herpesvirus to reproduce. Most veterinary texts suggested a lysine dose of 250-500 mg per day. I gave this supplement until the acute flare-up had resolved and I knew of many cat owners that continued the supplement indefinitely. However more recent better-designed  studies have found lysine to be ineffective in treating herpes infections in cats or in people. (read here  &  here)  Lysine can still be purchased at health food stores. If you or your veterinarian still choose to give it, pick a brand that is propylene glycol-free. Cats seem to dislike the taste of lysine when given alone. So most owners mix it with a small amount of food.

Some cats appear to be uncomfortable or experience eye pain during relapses, but many do not. If your cat is squinting or the eye is noticeably inflamed, atropine eye drops can be helpful during recovery. Cats on that medication (it dilates their pupils) seem more comfortable in subdued light – just as you do after an eye exam.

Most cats experience periodic herpes-1 relapses with no permanent eye damage other than the small white scars on their corneas that brought you to this page. But a few develop corneal flaps (tags) or non-healing areas that need to be surgically scraped and leveled to encourage proper healing. Some cats are left with long term tearing that persists even after the cornea has healed. A very few cats in which the eyelid experienced long-term inflammation, end up with hairs pointing toward the eye rather than away from it (entropion).

Eosinophilic Keratitis (aka keratitis – corneal inflammation)

Eosinophils are one of your cat’s immune system’s defensive cells. Eosinophilic keratitis (corneal damage) is one part of the many eosinophil-related diseases that affect cats. All result from your cat’s immune system making a mistake. (read here) When your cat’s eye(s) is involved, the eosinophils of your pet’s immune system increase in number within the several layers of the cornea – what should be the clear covering of the eye. When that happens, whitish raised plaques  – singular or multiple – become visible on the cornea of the affected eye. There is usually considerable mucus accumulation at the inner corner of the cat’s eye (its medial canthus) as well. Its 3rd eyelid is often more noticeable, extended and inflamed. Your veterinarian diagnoses eosinophilic keratitis by staining a gently-scraped preparation of your cat’s corneal cells and finding large numbers of eosinophils when the preparation is examined under a microscope. Untreated, this problem can lead to blindness. Treatment of eosinophilic keratitis is usually successful utilizing corticosteroid eye drops as well as medications that eliminate underlying secondary eye infections by mycoplasma and bacteria. When the problem is resistant, oral megestrol acetate (Megace®) can be effective – as it is in the other eosinophil-related diseases of cats. However, transient (or permanent) diabetes, weight gain, increased risk of mammary tumors, uterine infections in non-spayed females and liver toxicity are sometimes associated with that medication. Some veterinarians believe that herpes-1 eye infections are an underlying cause of eosinophilic keratitis. So if topical or oral corticosteroids are given to the cat to resolve eosinophilic keratitis, the cat needs to be closely monitored for a herpes-1 relapse because those same medication have been associated with reactivation of herpes-1. Eye irritation due to environmental contaminants and allergies also respond well to corticosteroid-containing eye drops – but the same cautions apply.

Dry Eyes =keratoconjunctivitis sicca

Eyes that lack sufficient tears can also be the underlying cause of superficial eye inflammation in cats. It can be diagnosed through a Schirmer tear test, a test that gauges the quantity of tears that are produced. As in humans, cats that do not produce enough tears are more subject to eye infections and corneal disease. (read here)

Cats that are squinting should have their eye(s) stained with fluorescein dye. That test allows your veterinarian to see early corneal ulcers and any cuts or abrasions and gauge their depth. Deep ulcers sometimes need a temporary emergency corneal “patch”.

How Can I Lessen The Likelihood Of Some OF These Problems Occurring In My Cat?

Some of the cats that suffer from these recurring eye problems test positive for  feline leukemia  or  feline immunodeficiency virus. So verify that your cat is both FLV and FIV negative. If it isn’t, your cat may be more subject to eye relapses and it may take longer and require more medications to help it recover. When those two underlying problems have been ruled out, lowering stresses in your cat’s life is the best preventative you have within your control. Hard as it is for many to accept, some of these cats will just be happier and do better in a single-cat household. Diets rich in vitamin A might also decrease the frequency and severity of relapses – but remember that too much vitamin A is also undesirable. Moderate portions of oily fish ( mackerel, salmon and tuna in that order) are probably the best natural sources.

Effective vaccines against herpes-1 are available. But to be effective, these vaccines must be given before this common virus infects a cat. That can be quite difficult because many kittens are already infected by their virus-shedding mother – even before their eyes open. The stress of pregnancy, and nursing, often causes these herpes-carrying mothers to relapse and pass the virus on to their kittens. The immaturity of the immune system of tiny kittens makes vaccines given at this early age unlikely to be effective. The vaccines used are part of the combination vaccines all veterinarians give to kittens at about 8-9 and 10-12 weeks of age. Many give a third booster at  ~14 weeks of age. The suggested timing differs slightly between manufacturers. Many cats from shelters are in the middle of a stress-induced relapse infection when I first see them. In those cats the vaccines is also likely to be less effective. Yearly booster vaccination against herpes-1/rhinotracheitis are probably unnecessary. There is quite a bit of evidence that herpes-1/rhinotracheitis, calicivirus and panleukopenia vaccines do not need to be given frequently or throughout your cat’s life. (read here)

All medications that turn down (lessen) the effectiveness of your cat’s immune system have the potential to allow feline herpes-1 virus to reactivate. Those medications include prenisolone, triamcinolone and other corticosteroids, cyclosporin (Atopica©), given to cats to help control skin allergies or to treat eosinophilic granuloma or to prevent organ rejection in cats that underwent kidney transplants.  This applies to all corticosteroids used to treat a variety of cat ailments – including asthma. (read here) Progestational drugs like megesterol can have similar effects. The diseases veterinarians opt to treat with those medications can be quite serious. So the small risk that these drugs might cause a herpes relapse in your cat is often preferable to withholding the medications. Similar corneal herpes reactivation due to corticosteroid or stress-related life events occur in people. (read here & here) However topical corticosteroid eye drops do not pose that reactivation risk – at least not in humans. In humans they actually speeded healing. (read here)

Bartonella

The bartonella organism can affect cats in many ways. (read here) It has been found that some cats with eye problems are positive for Bartonella. However just because your cat is PCR-positive for Bartonella does not mean that bartonella is the cause of its eye problem because so many cats carry bartonella (~6% in Illinois 33% in Florida, 40% in Poland). (read here) Bartonella responded well to treatment with doxycycline, azithromycin or rifampin antibiotics. When giving your cat capsules or tablets you should always follow the pill, capsule or tablet with a considerable amount of water or meat broth to keep capsules and pills from lodging in your cat’s throat (esophagus) and causing a stricture (=a scarred contraction causing swallowing difficulties).

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