CONDITION
Eosinophilic Keratitis in Cats
Eosinophilic keratitis is an inflammatory condition of the cornea—the clear surface of the eye—in which a particular type of immune cell, the eosinophil, accumulates in the tissue. This typically produces pink, white, or chalky raised areas on the cornea, often accompanied by thick discharge that may cling to the eye. The condition can affect one eye or both, tends to appear in adult cats (often around five years of age), and may come and go over time. Owners often notice a change in the appearance of the eye itself—an opaque patch or plaque that was not there before—or persistent discharge that does not clear with routine cleaning. The underlying cause remains uncertain, though the condition is considered immune-mediated and has been observed alongside feline herpesvirus infection in many cases, without proof that the virus directly triggers the corneal change. This page explores what eosinophilic keratitis may look like in practice, the mechanisms thought to be involved, how the condition is investigated (including sampling cells from the cornea), and the range of approaches used to manage inflammation and reduce recurrence. Long-term control, rather than cure, is often the realistic frame.
Why this matters now
Eosinophilic keratitis tends to appear in young to middle-aged cats, most often between two and nine years of age, with many cases presenting around five or six years. There is no established breed predisposition, though domestic shorthair cats make up the majority of reported cases, likely reflecting their prevalence in the general cat population. The condition can develop in cats of any breed, sex, or neuter status, though some studies have observed it more frequently in neutered males.
The condition often begins with a small, raised patch on the surface of the cornea, typically appearing at the outer upper edge of the eye and then spreading inward over weeks to months. The rate of progression varies considerably between individuals; in some cats the lesion remains relatively stable for long periods, while in others the pink or white tissue can gradually extend across more of the cornea, potentially affecting visual clarity if the central area becomes involved. Without intervention, the process tends to continue, though the pace and extent differ from case to case.
Signals & patterns
Early signals
Small cloudy or pink patch
A localised area of the normally clear cornea may develop a hazy, pinkish, or slightly raised appearance, often near the outer edge of the eye. This can look like a film or roughened texture on the surface that was not present before.
Mild squinting or blinking
The affected eye may appear slightly irritated, with the cat squinting more often than usual or blinking repeatedly on one side. This can be subtle and intermittent, particularly in the early stages.
Increased tearing or discharge
A small amount of clear or slightly cloudy discharge may appear at the corner of the eye, or the fur below the eye may look damp. This occurs as the surface of the eye responds to the underlying inflammation.
Change in eye colour or clarity
The eye may look less bright or clear than the other, with a faint white, pink, or chalky quality visible on part of the cornea when viewed from certain angles. Owners often notice this when comparing both eyes side by side.
Later signals
Spreading corneal lesion
The initial patch may extend across a larger portion of the cornea, sometimes covering much of the visible surface with a granular, fleshy, or velvety texture. This progression can unfold over several months and may affect one or both eyes.
Visible blood vessels on cornea
Fine blood vessels may become visible growing across the surface of the cornea toward or within the affected area, appearing as delicate red lines against the normally clear tissue. These represent the body's attempt to support the inflamed region.
Reduced vision or navigation changes
As more of the cornea becomes involved, the cat may show subtle changes in how it moves through familiar spaces, particularly if both eyes are affected or if the central visual axis is obscured. Many cats adapt well, especially when the change has been gradual.
Click to read about the biological mechanisms
How this is usually investigated
The diagnosis of eosinophilic keratitis typically begins with a detailed history and careful examination of the eye, particularly the cornea. The characteristic appearance—a pink or vascular raised lesion, often starting at the temporal limbus—can be strongly suggestive, but further investigation helps to confirm the presence of eosinophils, rule out other causes of corneal opacity, and identify any underlying or concurrent conditions that may influence management.
Physical examination
Cytology
Fluorescein staining
Histopathology
Herpesvirus testing
Options & trade-offs
Management of eosinophilic keratitis is typically ongoing rather than curative, with the aim of reducing inflammation, slowing lesion progression, and preserving corneal clarity and comfort. Most cats are managed with a combination of topical medications, and the choice of agents, frequency, and duration is tailored to the individual's response and the owner's ability to administer treatment. Different combinations suit different households, and what works well in one cat may need adjustment in another.
Topical corticosteroids
Corticosteroid eye drops or ointments—such as prednisolone acetate or dexamethasone—are often used to reduce the inflammatory response and eosinophil activity in the cornea. They are typically applied multiple times daily initially, with the frequency tapered as the lesion stabilises. Many cats show a reduction in the size, colour, and vascularity of the lesion within weeks to months of starting treatment.
Trade-offs: Long-term or frequent use of topical steroids can increase the risk of secondary bacterial or fungal infection, delay healing if ulceration is present, and in some individuals may contribute to glaucoma or cataract formation over time. They are generally avoided if there is an active corneal ulcer until the epithelium has healed.
Topical ciclosporin or tacrolimus
Topical immunomodulators such as ciclosporin or tacrolimus eye drops work by dampening the local immune response and reducing eosinophil infiltration without the broader effects of corticosteroids. These agents are often used as monotherapy or in combination with steroids, and may be particularly useful for cats requiring long-term control or those in which steroid side effects are a concern.
Trade-offs: Response can be slower than with corticosteroids, and some cats may require several weeks to months of consistent treatment before improvement is seen. The preparations can be more costly and may need to be compounded, and a small number of cats show irritation or discomfort with initial application.
Oral or topical megestrol acetate
Megestrol acetate is a progestogen that has been used in some cases to reduce eosinophil activity and inflammation, available as an oral tablet or as a 0.5% topical ophthalmic formulation. It has been documented in veterinary ophthalmology literature as an option for cats with eosinophilic keratitis, particularly when other treatments have been insufficient or poorly tolerated.
Trade-offs: Prolonged use of systemic progestogens can carry risks including diabetes mellitus, adrenal suppression, mammary hyperplasia, and behavioural changes, so this approach tends to be reserved for selected cases and used at the lowest effective dose for the shortest necessary duration. Topical formulations may reduce systemic exposure but are not widely available in all regions.
Topical antiviral agents
If there is concurrent evidence of feline herpesvirus infection or a strong clinical suspicion based on history and examination, an oral antiviral such as famciclovir (given by mouth, not as drops), or a topical antiviral such as idoxuridine, may be added to the treatment regimen. The rationale is to reduce viral replication that might be contributing to ongoing corneal inflammation.
Trade-offs: The evidence linking herpesvirus directly to eosinophilic keratitis is not definitive, so the benefit of antivirals in this specific context is uncertain. They add to the medication burden and cost, and their use is often guided by the presence of other herpetic signs rather than the corneal lesion alone.
Surgical debulking or superficial keratectomy
In cases where the lesion is large, raised, or causing significant visual impairment, surgical removal of the affected tissue—either by gentle debulking or a superficial keratectomy—can reduce the physical bulk of the lesion and may improve clarity. This is typically followed by ongoing medical management to prevent recurrence.
Trade-offs: Surgery requires general anaesthesia and carries the usual perioperative risks, and the lesion often recurs unless long-term topical treatment is continued. It can be a useful adjunct in selected cases but is not a standalone solution, and not all cats are suitable candidates depending on age, health, and extent of disease.
Common misconceptions
"Once the pink lesion has cleared, treatment can be stopped permanently."
Eosinophilic keratitis tends to be a chronic condition with a tendency to recur if medication is withdrawn. Many cats require long-term, sometimes lifelong, topical therapy at a reduced frequency to maintain control, and stopping treatment abruptly often leads to regrowth of the lesion within weeks to months.
"This condition will eventually cause complete blindness if left untreated."
Whilst untreated eosinophilic keratitis can lead to significant corneal opacity and reduced vision in the affected eye, total blindness from this condition alone is uncommon. Many cats retain functional vision, particularly if only one eye is affected or if the lesion progresses slowly. That said, ongoing inflammation and corneal change can affect quality of life and comfort, which is why management is often pursued.
"Eosinophilic keratitis is contagious to other cats in the household."
The condition itself is not contagious, as it represents an immune-mediated process within the individual cat's cornea rather than an infectious disease. Whilst some cats with eosinophilic keratitis may also carry feline herpesvirus, which can be transmitted, the corneal lesion itself does not spread directly from one animal to another.
Related conditions
Eosinophilic Granuloma Complex in Cats
Eosinophilic granuloma complex and eosinophilic keratitis share a common underlying pattern in which eosinophils infiltrate tissue and drive inflammation, though the former affects skin and mouth rather than the cornea. Both conditions can occur in the same individual cat and may respond to similar immunomodulatory approaches, though the triggers and tissue targets differ.
Corneal Ulcers
Corneal ulcers can develop as a consequence of eosinophilic keratitis when the inflamed, irregular corneal surface is injured through rubbing or secondary irritation. Distinguishing between the two is important, as an ulcer requires specific treatment to protect the corneal surface while the underlying immune process is managed.
Pemphigus
Uveitis may occur alongside eosinophilic keratitis in some cats, particularly when inflammation extends beyond the corneal surface or when a broader immune or infectious process is active. Both conditions can cause visible changes to the eye and discomfort, and uveitis may require additional investigation and treatment to prevent complications deeper within the eye.
Corneal Sequestrum in Cats
Corneal sequestrum can occasionally develop in eyes affected by chronic eosinophilic keratitis, as persistent inflammation and surface irregularity may create an environment in which areas of corneal tissue die and become isolated. The two conditions produce different appearances—sequestra are typically dark brown or black—but both involve chronic corneal disease in cats.
Keratoconjunctivitis Sicca (Dry Eye)
Keratoconjunctivitis sicca can be considered when investigating corneal changes in cats, as reduced tear production may lead to corneal inflammation that shares some features with eosinophilic keratitis. The two are distinguished by tear measurement and microscopic examination, and dry eye is far less common in cats than in dogs.
Because eosinophilic keratitis can coexist with other immune-mediated or allergic conditions, some owners find it useful to explore the broader patterns of immune and inflammatory health in their cat, particularly if there are signs affecting other body systems. The condition also raises questions about the role of chronic viral infection, environmental triggers, and the balance between controlling inflammation and minimising medication burden over time—themes that may be relevant in conversations at routine appointments or when planning long-term care.