Eosinophilic Keratitis in Cats

By Malcolm Weir, DVM, MSc, MPH; Catherine Barnette, DVM

Close-up of cornea ulcer in a cat

What is eosinophilic keratitis?

Feline eosinophilic keratitis is a chronic inflammatory disease of the cornea. In cats with eosinophilic keratitis, eosinophils (a type of white blood cell) invade the cornea, giving the surface of the eye a pink, white, and/or chalky appearance. Eosinophils may also invade the undersides of the eyelids and the thin conjunctival membrane that covers the sclera (white of the eye), creating even more widespread inflammation within the eye.

Eosinophils are cells that are typically involved in allergic reactions, as well as the body’s immune reaction to parasites.

What causes eosinophilic keratitis in cats?

The cause of feline eosinophilic keratitis or why the eosinophils invade the eye in these cats is currently unknown. Researchers have observed that up to 75% of cats with eosinophilic keratitis also have feline herpesvirus (an upper respiratory infection that can affect the eye); this suggests a possible link between the two conditions, but the details of this association are unknown.

Eosinophilic keratitis is most common in cats four years of age or younger. Additionally, the condition appears to be more common in neutered males, though the reason for this connection is unknown. Eosinophilic keratitis has been observed in domestic shorthair, domestic longhair, and purebred cats.

What are the clinical signs of eosinophilic keratitis?

Cats with eosinophilic keratitis develop characteristic raised pink, tan, white, or grey lesions on the surface of the cornea. These lesions may affect one or both eyes. Owners may initially notice the formation of new blood vessels at the edge of the cornea, soon followed by a white/grey film that develops on the surface of the cornea. Lesions are often first noticed at the edge of the cornea, sometimes extending from behind the third eyelid, but they will gradually spread across the cornea. Over time, the entire surface of the cornea may be affected.

"Over time, the entire surface of the cornea may be affected."

Chronic lesions may sometimes develop a gritty texture, due to calcium deposits within the lesions. The underside of the eyelids, as well as the third eyelid, may also become inflamed and thickened. Squinting and pain may develop, due to irritation from blinking and rubbing the eyelids across these raised, gritty lesions. Affected cats often develop thick ocular discharge, which may cling to the surface of the eye, and may also have constricted pupils (due to pain) and sensitivity to light.

How is eosinophilic keratitis diagnosed?

Diagnosis is often based largely on clinical signs. Confirming the diagnosis requires corneal cytology, which involves scraping a small sample off the surface of the eye and using a microscope to assess for the presence of eosinophils and mast cells (another type of inflammatory cell). Further testing may also be required to rule out other possible causes of corneal inflammation such as glaucoma, corneal ulceration, and inadequate tear production.

How is eosinophilic keratitis treated?

Eosinophilic keratitis is typically treated with topical steroid medication, though oral or injectable steroids may be required in severe cases. Because steroids can worsen corneal ulcers, they will need to be treated with antibiotics before starting steroids. Some cats may also receive topical medications to decrease pain and pupillary spasms. Because eosinophilic keratitis is often associated with feline herpes infection, antiviral medications may be used to decrease viral activity. Oral famciclovir (Famvir®) is sometimes prescribed, and cidofovir is used topically in the eye. Lysine, an oral antiviral medication that may suppress feline herpes infection, is also sometimes used.

"Surgical approaches have also been used to remove the abnormal tissue from the cornea of severely affected cats, but there are no clinical studies to support the use of this procedure."

Surgical approaches have also been used to remove the abnormal tissue from the cornea of severely affected cats, but there are no clinical studies to support the use of this procedure. Additionally, surgery requires that cats go through a period without steroid treatment, which may lead to worsening of the disease.

Frequent rechecks are often needed to monitor your cat’s response to therapy and adjust the treatment plan as needed. Medications will be tapered to the lowest effective dose; however, your cat will likely remain on lifelong therapy to prevent recurrence. If the eye was severely affected prior to starting treatment, corneal scarring or deposits may persist; however, it is often possible to provide good vision and quality of life for even severely affected cats if the medications are maintained as directed.

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