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It is quite common for cats to have eye irritation and eye mattering that comes and goes. In between relapses, nothing more might persists than pinpoint, rounded, milky corneal scars - like the orange tabby cat on the right. Do you see the two (. .) on the eye on the left ?
A scratch, dusty environment, allergies, dry eyes, tear duct or internal eye problems or unhealthy weight loss can all cause eye discharge or inflammation - but more commonly, it is due to persistent infections with 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 infection with Chlamydophila felis (aka Chlamydia
psittaci). Mycoplasma or a combination of two or more of any of them can also be involved.
When these organisms first infect your cat, they usually result in a generalized upper respiratory infections with fever, weepy eyes, crusty nose and sneezing (see Respiratory Infections In Your Cat). These infections usually clear up after a week or so with or without treatment, and most cats are never again bothered with the problem. But when the initial infection was with the cat herpes-1 virus (like human fever sore virus and chicken pox both other types of herpesvirus and both of which also remain dormant in our bodies) the virus never really leaves the cat's body. A few virus remnants remain dormant - but alive - sleeping in nerve tissue. In most cases, the cat's antibodies against them keep the virus in check. But stress and other factors that weaken the cat's immune system can allow the virus to awaken from its latency.
A small percentage of cats that become infected with Herpes-1 virus relapse from time. In most cats, these relapses are limited to nasal drainage, sinusitis or sneezing. Other cats simple begin shedding the virus again without evidence of illness. But in some, relapses occur in the clear, superficial layers of the eye (the cornea) with periodic drainage, inflammation and the formation of rounded milk white corneal scars- similar to the ones in the cat at the top of this article or more actively inflamed like this one. Some vets call this condition Herpesvirus keratoconjunctivitis or Infectious feline keratoconjunctivitis.
Between these episodes, the virus resides in the nerves of the face. Between episodes, 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 (or your dog) nor can human herpes infect them.
Flare-ups are often associated with the stress of boarding, weather change, other disease, new cats added to the family or new neighborhood cat rivalries. During these active virus periods 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 if they are not tended to and occasionally to sight-threatening penetration into the eye itself. That is why deep ulcers need immediate veterinary examination and care.
Can Other Problems Be Confused With Viral Or Bacterial Eye Infections ?
As I mentioned, there are non-infectious conditions that can mimic this disease. These include allergic and eosinophilic eye disease (read more about it further down), sensitivity to eye medications, environmental irritants or traumatic eye injuries (cats rub eyes that itch for any reason and the result can be corneal tears and scrapes; sharp claws occasionally tear the cornea during cat fights).
Diseases that increased ocular (eye) pressure or blood 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 Treatments Are Available For My Cat ?
Your veterinarian's visual inspection of your cat's eyes won't be 100% certain in diagnosing a herpes-1 viral problem - but there are very few other explanations for the distinctive scars this virus often leaves behind. So your veterinarian might add some other tests (like fluorescein dye examinations, swab cultures and cytology) to help rule out other causes or cases that might have multiple causes. When multiple pathogens are detected or suspected, your veterinarian might add antibiotics or anti-fungal agents that 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 stress levels are reduced. When the viral relapses linger - or when large portions of your cat's cornea are involved, the most effective treatment in 2015 still appears to be famciclovir (Famvir®), given by mouth 3 times a day. (ref) Older, less expensive, topical idoxuridine eye drops (Herplex®) are also effective - but you have to give them frequently throughout the day. (ref1, ref2) If you work schedule prevents that, 0.5% custom-compounded cidofovir eye drops given twice a day might be quite effective as well. (ref)
For many years, the amino acid, l-lysine, given twice a day, was thought to help many cases of Herpes-1/rhinotracheitis in cats to resolve and to, perhaps, 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. (ref1, ref2, ref3, ref4) I will probably no longer do that. In 2016, a review of the previously published information (the article links just above this and others) found that lysine may not possess the beneficial effects veterinarians thought it had ; and textbooks and mindsets are being revised to reflect that. (ref).
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 the cat is squinting or the eye is noticeably inflamed, atropine eye drops can help during recovery. Cats on that medication (it dilates the pupil) 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 small white scars on their corneas. But a few develop corneal flaps (tags) or non-healing areas that need to be surgically scraped and leveled for proper healing. Some cats are left with long term tearing that persists even after the cornea has healed and a very few cats in which the eyelid experienced long term inflammation, end up with hairs pointing into the eye rather than away from it (entropion).
Eosinophilic Keratitis (keratitis = corneal inflammation)
Eosinophilic keratitis is probably a part of the many eosinophil-related diseases that cats are susceptible to. (ref1, ref2) When the cat's eye(s) is involved, these cells of the cat's immune system increase in number within the several layers of the cornea - the clear covering of the eye. Whitish raised plaques - singular or multiple - are visible on the cornea of the affected eye. There is usually considerable mucus accumulation at the inner corner of the eye (the medial canthus) as well and the cat's 3rd eyelid is often more noticeable and inflamed. Your veterinarian diagnoses eosinophilic keratitis by staining a preparation of the cat's corneal cells and finding large numbers of eosinophils when the preparation is examined under a microscope. Untreated, the problem can lead to blindness. Treatment of the condition is usually successful utilizing corticosteroid eye drops as well as medications to eliminate underlying problems such as mycoplasma or bacteria. When the problem is resistant, oral megestrol (Megace®) can be effective - as it is in the other eosinophil-related diseases of cats. However, transient diabetes, weight gain, increased risk of mammary tumors, uterine infections and liver toxicity are sometimes associated with that medication. Some veterinarians believe that herpes-1 eye infections are a common underlying cause of eosinphilic 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 the same medication has been associated with reactivation of herpes-1. Eye irritation due to environmental contaminants and allergies also respond well to corticosteroid-containing eye drops.
that are squinting should have their eyes stained with fluorescein
dye. This allows veterinarians to see early corneal ulcers and gauge their
depth. Deep ulcers sometimes need a temporary emergency corneal
How Can I Lessen The Likelihood Of This Problem In My Cat ?
A portion of the cats that have these recurring eye problems have tested positive for feline leukemia or feline immunodeficiency virus. So verify that your cat is both flv and fiv negative. If it isn't, the 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 the stresses in your cat's life is the best preventative you have that is within your control. Hard as it is to accept, some of these cats will just be happier and do better in a single-cat family. Diets rich in vitamin A may also decrease the frequency and severity of relapses - but too much vitamin A is also undesirable. Effective vaccines against herpes-1 are available. But to be effective, the vaccine must be given before this common virus infects the cat. That is quite difficult because many cats are already infected from their virus-shedding mother - even before their eyes open. The stress of pregnancy, and more so nursing, causes these carrier mothers to relapse and infect their kittens. The vaccine is part of the combination vaccine all vets give to kittens at 12 and 14 and 16 weeks of age. Many cats from shelters are in the middle of a stress-induced relapse infection when I first see them. In these instances the vaccines will also not work. Yearly booster vaccination against herpes-1/rhinotracheitis is ineffective and unnecessary. There is plenty of evidence that herpes-1/rhinotracheitis and Calicivirus vaccines do not need to be given throughout life. (ref)
All medications that lessen the effectiveness of your cat's immune system have the potential to allow feline herpes-1 virus to reactivate. Those medications include cyclosporin (Atopica©), given to cats to help control skin allergies, eosinophilic granuloma or to prevent organ rejection. It applies to all corticosteroids used to treat a variety of cat ailments - including asthma. (ref) Progestational drugs like megesterol can have a similar effect. The diseases veterinarians treat with those medications can be quite serious. So the small risk that these drugs might cause a herpes relapse is often preferable to withholding the medications.
The bartonella organism can affect cats in many ways. (ref) Recently, it was found that some 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 or meat broth to keep capsules and pills from lodging in your cat's throat and causing a stricture (a scarred contraction, swallowing blockage ).
Newer Diagnostic Tests
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 [ref1 , ref2] ). If your kitty has only a persistent eye problem, some of these organisms are not likely to be the cause; but the panel tests for all of them. Its limitation is that the most common cause, the Herpes-1 (rhinotracheitis virus/cat flu) 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.