Ron Hines DVM PhD
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The clear outer capsule of your pet's eye is called the cornea. Corneal cells are the only cells in the body that are transparent.
Instead of being nourished by blood vesicles, the clear cornea is bathed in a nourishing protective liquid, the tears. Because of its delicate nature, and its position on the outermost edge of the eye, your pet's cornea is subject to scratches, scrapes and ulceration.
When the scrape or scratch is shallow, the cornea heal very rapidly. These shallow scrapes and scratechs are most common in young active animals.
But older dogs and Persian cats are more subject to slower-healing erosions of the cornea called ulcers. The most common cause of these ulcers is a lack of protective tears - but they can also be due to bacterial and fungal infection. Adult cats also develop these ulcers due to infection with feline herpesvirus-1. Left untreated, corneal ulcers can develop serious complications that can destroy vision.
Ulcers of the cornea may be shallow or deep. They result from everything from pawing to bee stings, the scratch of a thorn or an infectious bacteria. Once the outermost layer of the cornea has been torn, the area becomes irritated and painful. This causes the pet to squint and the eye to tear. We call this reflex blepharospasm.
Corneal ulcers are quite painful and they itch. In response, your pet will rub the affected eye causing the problem to become worse. A discharge may accumulate in the corner of the eye nearest the nose and the blood vesicles of the white of the eye (sclera) enlarge with blood. If the damaging object is no longer in the eye and the ulcer is not deep it will heal.
However if an infection is present, the ulcer may progress to affect the deeper layers of the cornea. Once much of the cornea has been eroded away a bulge may form similar to a sidewall blowout on a tire. Such a bulge is called a descemetocele. If a descemetocele bursts, the anterior portion of the eye will collapse and the contents will spill out destroying the eye. This is why all corneal ulcers need to be observed closely and frequently by your veterinarian.
Large, corneal abrasion, and ulcers causes the entire cornea to swell with fluid (edema) and the cornea to turn white in color. If the eye is normal, within a few days tiny blood vessels will form in the cornea to aid in the healing process.
Corneal ulcers are graded according to their depth. If only the outer layer is lost the lesion is called a superficial corneal ulcer. When more than one half the thickness of the cornea is lost it is called a deep corneal ulcer. Superficial ulcers in health eyes heal in a matter of days. Deep ulcers may take several weeks to heal. Deep ulcers require new blood vesicles to grow into the area. They may also leave a corneal scar. When there are underlying causes for the ulcer, some refuse to heal or heal only to re-ulcerate again.
How Do We Diagnose Corneal Ulcers?
Corneal Ulcers Due To Accidents:
Scraping and puncture wounds of the eye are the most common cause of corneal ulcers in dogs. Cats are less likely to poke their eyes with blunt or sharp objects or to damage the cornea with their claws while scratching. These ulcers are often linear or oblong in shape. If they are not deep they tend to heal quite rapidly.
Corneal Ulcers Due To Eye Conformation:
Dogs and cats with bulging eyes are more susceptible to corneal ulcers. This is because bulging eyes are more likely to be scraped and scratched. Misplaced eyelashes (dystrichiasis) and eyelids that curl inwardly (entropion) or outwardly (ectropion) can also cause corneal ulcers. Shar pei and Chow Chows commonly suffer from entropion. Hound breeds are prone to ectropion.
Corneal Ulcers Due To Dry Eyes:
film of tears over protruding eyes often does not reach the center.
Dryness of the eye is sufficient to cause ulceration. Other pets
are born with deficient tear production. Tear flow over the eye
can be increased using cyclosporin ophthalmic drops or corrective
surgery. The use of antibiotics of the sulfa class has also been
associated with dry eye syndrome. The medical term for dry eye is
keratoconjunctivitis sicca (KCS).
Corneal Ulcers In Cats Due To Herpesvirus-1 Infection:
The rhinotracheitis or herpes-1 virus can form a carrier state in the eyes of cats causing periodic corneal ulcers. These ulcers come and go with stress. When inactive, the cornea is left with milky white rounded scars. If this disease is suspected and the signs are severe and persistant, the cat should recieve topical antiviral drugs such as diluted trifluridine(Viroptic,trifluorothymidine).
The amino acid, l-lysine, has been found to help many cases of rhinotracheitis conjunctivitis 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 suplement until the acute flare-up has resolved. But many cat owners continue the suplement indefinitely. Lysine can be purchased at health food stores. Pick a brand that is propylene glycol-free.
Please also read: http://www.2ndchance.info/respiratorydiscat.htm and http://www.2ndchance.info/cateye.htm and http://www.2ndchance.info/cough.htm and http://www.2ndchance.info/rhinotracheitis.htm and http://www.2ndchance.info/sneezing.htm ).
This rare condition is characterized by abnormal deposits within the cornea, which contain calcium and cholesterol. It is sometimes associated with hypothyroidism.
Boston Terriers and Boxers have corneas that just do not seem to heal well. When these breeds develop corneal ulcers vitamin E solution may hasten healing.
Corneal Ulcers Due To Bacterial Or Fungal Infection:
Certain bacteria have an affinity for the eye causing redness and itching. Self-trauma in these cases can cause corneal ulcers. These cases need to be placed on antibiotic or antifungal eye drops.
Indolent ulcers are ulcers that refuse to heal. These can occur when a ledge of dead corneal tissue surrounds the ulcer. These ulcers can be encouraged to heal if this dead tissue is scraped away. Other causes are persistent dry eye, infection, or concurrent disease in your pet that slows the healing process. These long-standing ulcers also respond when the third eyelid is sutured across the defect in a procedure called tarsorrhapy.
Corneal Ulcers That Progress To A Descemetocele:
Some corneal ulcers become so deep that the inner lining, Descemet’s membrane, balloons out forming a descemetocele, which is similar to sidewall damage on a tire. If this structure ruptures, fluid from the anterior chamber of the eye leaks out over the cornea and the eye collapses. The iris in these eyes becomes sticky and will often stick to or protrude through the defect. When these eyes heal the normal anatomy of the eye does not recover. Distortions of the iris in these eyes often leads to glaucoma and loss of vision or the eye when the iridocorneal angle is changed (see diagram).
Cats Positive For Bartonella Infection
A high percentage of cats with inflammations of the eye are also positive for bartonella. These cats often get better when they are given azithromycin, doxycycline antibiotic, or rifampin. Azithromycin is probably the best choice because it also kills other organisms that can be involved in these conditions (mycoplasma). When giving these medications in solid form to cats, you should follow by giving the pet water so that the medication does not lodge in the throat.
General Treatment Of Corneal Ulcers:
The treatment I prescribes for dogs and cats with corneal ulcers depends on the severity of the ulcer, how long it has been present and what I feel is the underlying cause of the problem.
I focus on treating and preventing secondary infection, controlling inflammation and pain , preventing additional corneal damage, and minimizing damage to the cornea by limiting scar formation.
Cats with persistent viral-induced corneal ulcers receive anti-viral ointments or drops.
Deep corneal ulcers need more complicated treatment. Since these cases can be medical emergencies I usually hospitalize these pets. If Descemet’s membrane is bulging through the ulcer I anesthetize these pets. As much tissue as possible is replaced through the ulcer. I will often reinforce the area of the ulcer with very fine suture material and then sew a patch composed of an attached slice (flap) of the third eyelid over the ulcer to shield it and bring it a blood supply. When I am through with this surgery I suture the lower lid over the eye to protect it. After three weeks these ulcers have usually healed sufficiently for the patch to be removed. If Descemet’s membrane has burst and the eye has already leaked its contents, the outcome of this surgery is less successful. Some of these eyes cannot be saved. Short-faced (bracheocephalic) breeds of dogs such as Pekingese and Lhasa Apsos are particularly prone to this condition.
Ointments and drops need to be applied very frequently to affected eyes. I generally suggest every two to four hours in newly treated eyes. During this time the pet must be observed closely so that it does not rub or scratch the eye.
the pet developed an ulcer because of insufficient tears (keratoconjunctivitis
sicca) or a bulging eye I often place them on cyclophosphomide eye
drops or artificial tears. An alternative to this is surgical transplantation
of the duct of the salivary gland.
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 cats.(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.