Telltale signs: squinting and red eyes: if untreated, corneal ulcers can develop serious complications, causing the permanent loss of sight.
Yet another telling sign is a discharge from the eye. This can range from tearing to a thick secretion. An opaque white, yellow or blue coloration may also be noticeable. Eventually, the discoloration and a cloudiness of the cornea can prevent light from entering the eye and result in blindness.
Healthy Cornea. "The cardinal signs of a corneal ulcer include discomfort, ocular discharge, redness of the white of the eye and the opacity of the cornea itself," says ophthalmologist Eric C. Ledbetter, DVM, DACVO, at Cornell University Hospital for Animals. "The cornea should be clear, and with an ulcer it often becomes opaque."
Left untreated, corneal ulcers can develop serious complications that may compromise visual acuity and permanently destroy a cat's sight if a veterinarian doesn't promptly treat it.
The cornea consists of the epithelium, which are the cells in the outermost layer; the stroma, which is comprised of connective tissue cells; the endothelium, a single layer of cells whose primary function is to maintain the cornea in a dehydrated state to help achieve optical clarity; and the Descemet's membrane, a thin, strong tissue that protects against infection and injury.
A corneal ulcer is an erosion of the epithelium into the stroma, where fluid from tears gives the cloudy appearance to the eye. If the erosion continues to Descemet's membrane, a deep ulcer called a descemetocele forms. Then the eye may leak and can collapse, Dr. Ledbetter says. At this stage, surgery and tissue grafting may be necessary. "The tissue is usually harvested from the cat's own eye, but synthetic and other biological graft materials are also available," he says. "Some eyes can be saved with surgery."
Corneal ulceration has many causes, but feline herpesvirus virus (FHV-1) is overwhelmingly the most common, Dr. Ledbetter says. The highly contagious virus is transmitted by contact with saliva, ocular or nasal secretions, such as sneeze droplets, shared food and litter. The virus replicates within corneal cells and destroys them, requiring treatment with topical drugs or antiviral medication.
FHV-1 infection typically occurs in kittens, with an estimated 80 percent progressing to latent infection, and 45 percent of those experiencing spontaneous reactivation of the virus later in life, according to a study published in 2010 in Journal of Feline Medicine and Surgery.
Among the many other causes of corneal ulcers in cats:
* External injury resulting from fights, accidents, thorns or other sharp or abrasive objects coming into contact with the eye. These injuries can reduce the cornea's anatomical and physiological defenses and result in secondary corneal infections.
* Facial nerve paralysis: This can cause a disorder in a cat's blink reflex--an important function in protecting the eye. Causes can include inflammation of the middle ear or petrous temporal bone, a dense pyramid-shaped bone at the base the skull, post-surgical complications or trauma.
* External irritation: According to the Cornell Feline Health Center, other causes include ingrown eyelashes, dirt trapped beneath the eyelid or exposure to caustic or harmful chemicals such as shampoos and household cleaners.
* Bacterial infection: A variety of bacteria can infect the eye, so a culture is often needed to determine the correct antibiotic to be used.
An ulcer's progress depends on a number of factors, especially how quickly a veterinarian attends to it. A corneal ulcer can heal in a week or less with medical care. Without it--or if a cat's immune system is weakened--the body tries to heal the cornea by sending blood vessels into the cornea. This can cause the cornea to swell and become susceptible to invading bacteria that can erode it.
Specific breeds are more susceptible to corneal ulcers, particularly short-faced cats bred to achieve a baby-like appearance, Dr. Ledbetter says. "Himalayans and Persians are kind of the poster children. They've been bred for a very specific facial look, which is more human-like and it's at the cost of protecting their eyes."
Other flat-faced breeds are the British Shorthair, Scottish Fold, Munchkin and Selkirk Rex. Their prominent eyes put them at risk of eye trauma when they run into an object or a sharp paw in a scuffle with another cat.
Testing for Tears. In an ophthalmic exam, veterinarians will stain the eye with fluorescein, an orange substance that fluoresces under a blue light to highlight foreign bodies and damage to the cornea. They might also test for tear production, obtain cultures and perform a microscopic examination of tissue.
Compared with dogs, the cause of feline corneal ulcers is more often viral, Dr. Ledbetter says. "Goal No. 1 of treatment should always be to identify and eliminate the underlying cause whenever possible."
After the cause is found and removed--or in the case of a wound, healed--the next step is to prevent secondary infections and apply a topical antibiotic or administer an antiviral medication if the cause is viral.
Antibiotic drops may be applied but are effective only for several hours. They must be applied frequently, so often longer-lasting ointments are applied. In some cases Dr. Ledbetter prescribes a drug called atropine to help control pain. A side effect is that it makes a cat light-sensitive, even for days after the medication is halted.
Atropine is known to have a bad taste, and if it gets in a cat's mouth during application, drooling can occur for a period of time. An uncomfortable cat can understandably make the next application more difficult.
The Follow-ups. A patient should be re-examined after two to three days of treatment to ensure that healing is progressing. If the ulcer isn't healing well, additional treatments or surgery may be necessary.
In addition to the cost of an Elizabethan collar as a protective measure, the fees for treating a cat with a corneal ulcer will vary from clinic to clinic, Dr. Ledbetter says. "The costs are much lower when getting appropriate treatment earlier than if treating secondary complications, such as infections. Then the costs will rise substantially."
As for recovery, he says, "In general, if it's an uncomplicated ulcer, then the prognosis is good. With secondary causes or if the problem is repetitive, then it can be guarded or poor. The critical message should be to seek appropriate care early."
THE ANATOMY OF THE CORNEA
The cornea, the clear coating of the eye that admits light, has layers of specialized skin cells, including:
* Epithelium, the outer layer of tissue covering the cornea, keeps foreign material, such as dust, water and bacteria, from entering the eye. It also absorbs oxygen and cell nutrients from tears and distributes them to the rest of the cornea. Its tiny nerve endings make the cornea sensitive to pain when rubbed or scratched.
* Stroma is connective tissue cells composed of water and flattened plates of collagen fibers that provide strength, elasticity and form to the cornea.
* The endothelium, a single layer of cells, mainly keeps the cornea dehydrated to maintain vision.
* Descemet's membrane, the "basement" of the endothelium, consists of transparent tissue--collagen fibers differing from those in the stroma --covering the inner surface of the cornea. It's named after the 18th-century physician Jean Descemet.
|Printer friendly Cite/link Email Feedback|
|Date:||Mar 1, 2015|
|Previous Article:||A cat on an underwater treadmill? Rehabilitation goes mainstream as Cornell offers therapies to promote mobility and manage pain.|
|Next Article:||A new biomarker detects kidney disease early on.|