Keratitis in Cats: Corneal Inflammation — Causes, Signs, and Treatment

Oct 22 • 10 min read

Your cat's eye has developed a strange white or pink patch on the surface, and it doesn't look like a typical scratch. Or maybe the whole cornea has gone hazy and blue-white, and you can't tell if she's in pain or not. The clear surface of the eye is supposed to stay, well, clear, and something has clearly disrupted it.

Keratitis simply means inflammation of the cornea, the clear front surface of the eye. It's a common and often painful eye condition in cats, and it can be triggered by trauma, infection, dry eye, or an unusual immune-mediated condition unique to cats and horses called eosinophilic keratitis. Treatment depends entirely on identifying the underlying cause, since some medications that help one type of keratitis can seriously worsen another.

Key Takeaways

Keratitis means inflammation of the cornea, and it can be either ulcerative (with a break in the corneal surface) or non-ulcerative (without one).
Ulcerative keratitis is most commonly caused by trauma or feline herpesvirus-1 (FHV-1).
Non-ulcerative keratitis includes eosinophilic keratitis, a unique immune-mediated condition often linked to FHV-1, along with dry eye and other causes.
Signs include cloudiness, redness, squinting, discharge, and visible plaques or lesions on the cornea's surface.
Diagnosis almost always starts with a fluorescein stain test, since treatment differs dramatically depending on whether an ulcer is present.
Never use steroid-containing eye medication on a cat's eye without veterinary confirmation that no ulcer is present, since steroids can make an ulcer significantly worse.

What Is Keratitis in Cats?

Diagram comparing ulcerative and non-ulcerative keratitis in cats

Keratitis is the general medical term for inflammation of the cornea, the clear, dome-shaped layer at the very front of the eye that protects the inner structures and helps focus light. When the cornea becomes inflamed, it can lose its normal transparency, taking on a cloudy, white, pink, or hazy appearance that affects both how the eye looks and how well your cat can see.

Vets generally divide keratitis into two broad categories, and figuring out which one your cat has completely changes the treatment approach:

Ulcerative keratitis means there is an actual break or erosion in the corneal surface, essentially a corneal ulcer. This form is usually quite painful, since the cornea is packed with nerve endings, and cats with it tend to squint hard, tear excessively, and rub at the eye.

Non-ulcerative keratitis means the cornea is inflamed without any break in its surface. This category includes conditions like eosinophilic keratitis, a distinctive immune-mediated condition, along with inflammation related to dry eye, viral disease, or other underlying causes. Non-ulcerative keratitis can sometimes be less obviously painful than the ulcerative form, though it still needs treatment.

Importantly, one form can turn into the other. Non-ulcerative keratitis that goes untreated can eventually develop an ulcer on top of it, which is one of several reasons why any ongoing corneal inflammation deserves veterinary attention rather than a wait-and-see approach.

Signs of Keratitis in Cats

Watch for the following signs, which can appear in different combinations depending on the underlying cause:

Cloudiness, haziness, or a blue-white color change on the eye's surface
Redness of the eye or surrounding tissue
Squinting or holding one eye partly or fully closed
Excessive tearing or discharge, which can be watery, mucoid, or thicker
Visible white, pink, tan, or gray raised plaques on the cornea's surface
New blood vessels growing across the edge of the cornea
Pawing at the eye or rubbing the face against furniture
Light sensitivity
A gritty or rough-looking texture developing on chronic lesions

Eosinophilic keratitis specifically often starts as raised pink, tan, white, or gray lesions near the edge of the cornea, sometimes extending from behind the third eyelid, that can gradually spread to cover more of the corneal surface over time. Ulcerative keratitis, by contrast, tends to come with more obvious pain signs from the start.

What Causes Keratitis in Cats?

Trauma is the most common cause of ulcerative keratitis. This includes scratches from another cat during play or a fight, plant material or debris getting into the eye, or self-inflicted damage from rubbing an already irritated eye.

Feline herpesvirus-1 (FHV-1) is an especially important cause in cats, and it's linked to both major types of keratitis. It's a very common trigger for corneal ulcers, and it's also strongly associated with eosinophilic keratitis specifically, with studies finding the virus present in a large majority of cats diagnosed with that condition. Because FHV-1 is so common in the general cat population, many vets approach keratitis in cats with the assumption that herpesvirus involvement is possible until proven otherwise.

Eosinophilic keratitis is a distinctive, immune-mediated form of non-ulcerative keratitis where a type of white blood cell called an eosinophil, normally involved in allergic responses, invades the cornea. The exact trigger isn't fully understood, but the strong association with FHV-1 suggests the virus plays some role, even though the details of that connection remain unclear.

Dry eye (keratoconjunctivitis sicca) is another cause of non-ulcerative keratitis, where reduced tear production leaves the corneal surface without enough protection and lubrication, leading to chronic irritation and inflammation over time.

Other causes include bacterial, fungal, or parasitic infection, immune-mediated disease, and exposure-related irritation, particularly in cats whose eyelids don't fully close or protect the eye.

How Is Keratitis Diagnosed?

Diagnosis always starts with a thorough eye exam. Your vet will look closely at the cornea's clarity, texture, and any visible lesions, along with the eyelids, conjunctiva, and tear film.

A fluorescein stain test is a critical step, since it's the primary way to determine whether an ulcer is present. This distinction matters enormously for treatment, because some medications used for non-ulcerative keratitis, particularly steroid eye drops, can significantly worsen an ulcer if one is present and undiagnosed.

Flowchart showing the diagnostic pathway for keratitis in cats

If eosinophilic keratitis is suspected based on the classic appearance of raised plaques, your vet may recommend a corneal cytology sample, collected gently with a special brush or the blunt edge of a tool, to look for eosinophils under the microscope and confirm the diagnosis. A Schirmer tear test may also be used to check tear production if dry eye is a possibility.

"Cats with keratitis should be assumed to have herpesvirus until proven otherwise." — Today's Veterinary Nurse, What Is Wrong With My Patient's Cornea? Nonulcerative Keratitis in Veterinary Medicine

Treatment Options for Keratitis in Cats

Infographic comparing ulcerative and non-ulcerative keratitis causes and treatment in cats

Treatment for keratitis depends entirely on which type your cat has and what's driving it.

For ulcerative keratitis (corneal ulcers), treatment typically includes a topical antibiotic to prevent or treat secondary infection, pain control, and an e-collar to prevent rubbing that could worsen the injury. If feline herpesvirus is suspected as the trigger, an antiviral medication like famciclovir may be added. Steroid-containing medications are avoided until the ulcer has healed, since they can interfere with corneal healing and worsen the ulcer.

For non-ulcerative keratitis, including eosinophilic keratitis, treatment often centers on topical anti-inflammatory medication, most commonly a steroid, once your vet has confirmed through fluorescein staining that no ulcer is present. In some cases, oral or injectable steroids are used for more severe or widespread disease. Because eosinophilic keratitis is frequently linked to FHV-1, antiviral medication or lysine may also be part of the plan, depending on your vet's assessment. If an ulcer is found at the edges of an eosinophilic lesion, which does happen, antibiotics are typically added first before any steroid is introduced.

For dry eye-related keratitis, treatment focuses on restoring tear film support, which may include lubricating eye drops, medications aimed at stimulating tear production, or addressing an underlying cause if one is identified.

Because these treatment paths can be quite different from one another, and because using the wrong medication for the wrong type of keratitis can genuinely make things worse, an accurate diagnosis really does need to come before treatment starts.

Why Steroid Eye Drops Require Extra Caution

It's worth repeating clearly: steroid-containing eye medications are genuinely useful for certain types of keratitis, particularly eosinophilic keratitis, but they can be harmful if a corneal ulcer is present and undiagnosed. This is exactly why your vet needs to perform a fluorescein stain before starting any steroid treatment, and why using leftover eye drops at home, even ones that worked for a previous eye problem, carries real risk. Never start or continue a steroid eye medication on your cat without a current veterinary exam confirming it's the right choice for what's happening in that eye right now.

Living With Recurrent Keratitis

Because feline herpesvirus is such a common underlying factor, some cats experience keratitis that returns periodically, particularly during periods of stress. A few things can help manage this over the long term:

Keep all recheck appointments so your vet can confirm healing and catch any recurrence early
Reduce stress at home where possible, since stress is a known trigger for herpesvirus reactivation
Ask your vet whether ongoing antiviral support or lysine makes sense for your cat's specific pattern of flare-ups
Watch for early signs of a new episode, such as squinting, redness, or a return of cloudiness, and don't wait to have it checked
Keep an e-collar on hand for future flare-ups, since preventing rubbing helps protect a healing or inflamed cornea

FAQ Section

Is keratitis in cats painful?
It depends on the type. Ulcerative keratitis, involving an actual break in the corneal surface, is usually quite painful and causes obvious squinting and discomfort. Non-ulcerative forms like eosinophilic keratitis can sometimes be less obviously painful, especially early on, though this varies between cats.

What is eosinophilic keratitis in cats?
Eosinophilic keratitis is a distinctive, immune-mediated form of non-ulcerative keratitis where a type of white blood cell called an eosinophil invades the cornea, creating raised white, pink, tan, or gray plaques. It's strongly linked to feline herpesvirus-1, though the exact relationship isn't fully understood.

Can I use my cat's old eye drops if her eye looks inflamed again?
No. Never use leftover eye medication, especially anything containing a steroid, without a current veterinary exam. The right treatment depends on whether a corneal ulcer is present, and using the wrong medication, particularly a steroid on an undiagnosed ulcer, can make the problem significantly worse.

How is keratitis different from a corneal ulcer?
A corneal ulcer is one specific cause of keratitis, specifically the ulcerative type, where there's an actual break in the corneal surface. Keratitis is the broader term for corneal inflammation and also includes non-ulcerative forms, like eosinophilic keratitis, where the surface isn't broken but the cornea is still inflamed.

Is keratitis in cats linked to feline herpesvirus?
Very often, yes. FHV-1 is a leading cause of ulcerative keratitis (corneal ulcers) in cats, and it's also strongly associated with eosinophilic keratitis, a form of non-ulcerative keratitis. Because the virus is so widespread in cats generally, many vets consider herpesvirus involvement likely in keratitis cases until it's ruled out.