Keratitis in Cats: Symptoms, Causes, Treatment & Emerging Therapies

What Is Keratitis in Cats?

Keratitis is inflammation of the cornea, the clear, dome-shaped window at the front of your cat's eye, and it is one of the most important eye conditions owners should learn to recognize. ^{[1, 2, 3]}

Unlike conjunctivitis, which affects the pink membranes around the eyeball, keratitis targets the cornea itself, the transparent layer that lets light reach the retina ^{[2, 3]}. Because the cornea must stay crystal-clear to focus light properly, any inflammation can cause cloudiness, the growth of new blood vessels into the cornea, and even permanent pigment deposits that block vision ^[1].

Vets typically classify keratitis in two main ways: by whether the corneal surface is broken (ulcerative) or intact (non-ulcerative), and by whether the disease is short-term (acute) or long-standing (chronic) ^{[1, 4]}. Both classifications matter because they dictate treatment, so getting the right diagnosis quickly is essential to protecting your cat's sight.

Types of Keratitis in Cats

There is no single form of feline keratitis, the umbrella term covers several distinct diseases with different causes, appearances, and treatments. Understanding which type your cat has is the first step toward the right care.

Ulcerative keratitis is the form where the corneal epithelium (the thin surface layer) has been eroded, exposing the underlying stroma. Ulcers are graded by depth, superficial, deep stromal, or descemetocele (a very deep ulcer exposing the innermost corneal layer), and by their healing behavior, with "indolent" or non-healing ulcers being particularly stubborn. Persistent ulcers can progress to corneal sequestrum (a discolored, dead patch of cornea) or even perforation if not addressed ^{[5, 3]}.

Non-ulcerative keratitis describes inflammation that occurs beneath an intact corneal surface, often driven by immune dysregulation or chronic irritation ^[1]. Within this category sits eosinophilic keratitis (FEK), a chronic, progressive disease in which eosinophils (a type of allergy-linked white blood cell) and mast cells invade the cornea, producing raised pink, white, or tan plaques. It often starts in one eye but can become bilateral (affecting both eyes) ^{[6, 2, 7, 8]}.

Other forms include pigmentary keratitis, where brown or black pigment is deposited within the cornea as a chronic response to irritation, and herpetic keratitis, caused by feline herpesvirus-1 (FHV-1), which produces characteristic branching (dendritic) or geographic ulcers ^{[1, 4, 5, 9]}. Keratitis is also commonly categorized by its underlying trigger: infectious (viral, bacterial, fungal, or amoebic), immune-mediated, traumatic, or secondary to eyelid and tear film problems ^{[2, 4, 5, 1]}.

Causes and Triggers of Keratitis

The single biggest cause of feline keratitis is a virus almost every cat has already been exposed to, feline herpesvirus-1 ^{[4, 9]}.

FHV-1 has a worldwide distribution, with reported exposure rates in some cat populations of up to 97%. As such it is a significant cause of clinical disease in the global cat population. Following exposure to the virus, virtually all cats become persistently infected and many of these will develop recrudescent disease on one or more occasions during their lifetime. When stress, illness, or immunosuppression triggers viral reactivation, it can cause recurrent, painful corneal ulcers and keratitis that may flare repeatedly over many years ^{[4, 9]}.

Other infectious causes include bacterial keratitis, which often follows corneal trauma or ulceration and may involve bacteria such as Staphylococcus, Klebsiella, Corynebacterium, and Enterococcus; fungal keratitis, which is rare but possible after corneal injury in immunocompromised cats; and Acanthamoeba castellanii keratitis, caused by a free-living amoeba acquired from contaminated water or soil, particularly when there is a pre-existing corneal abrasion ^[5].

Non-infectious triggers are just as important. Immune-mediated keratitis (including eosinophilic keratitis and pannus) appears to be an exaggerated immune response to an unknown antigen, with possible links to feline herpesvirus ^{[2, 7, 6, 10]}. Traumatic causes include scratches, foreign bodies, and adnexal (eyelid-related) abnormalities such as ingrown eyelashes (ectopic cilia or distichiasis) and inward-rolling eyelids (entropion) ^{[4, 1]}. Secondary keratitis can also arise from dry eye (keratoconjunctivitis sicca), tear film instability, facial nerve paralysis, or incomplete eyelid closure ^{[4, 2]}.

Some patterns emerge across cases. Breed predispositions exist for certain forms of corneal ulceration, with Persian, Burmese, Himalayan, and Siamese cats more often diagnosed ^[4]. Age matters too, eosinophilic keratitis most commonly strikes cats around 5 years old ^{[2, 8, 7]}. Interestingly, neutered males appear slightly overrepresented in eosinophilic cases, though the reason is unknown ^[7].

Is Keratitis in Cats Contagious?

Keratitis itself is not contagious, but whether it can spread to other cats depends entirely on what's causing it.

When keratitis is caused by feline herpesvirus-1 (FHV-1), the virus is highly contagious between cats through direct contact, aerosol droplets from sneezing, and shared objects (food bowls, bedding, toys) ^[9]. Because the virus is essentially ubiquitous in cat populations, multi-cat households and shelters are particularly prone to outbreaks of herpetic eye disease.

In contrast, Acanthamoeba keratitis cannot be passed from cat to cat, the amoeba lives in water and soil environments ^[5]. Bacterial and fungal keratitis are also not typically contagious between cats; transmission would only be a theoretical concern in severely immunocompromised housemates. Immune-mediated, traumatic, and secondary keratitis are entirely non-infectious and pose no contagion risk to other animals or people.

The good news for owners: you cannot catch keratitis from your cat. Practicing good hygiene (washing hands after handling eye discharge) is still wise, but the disease is feline-specific. If your cat has herpetic keratitis, however, isolating affected cats from herpesvirus-naive housemates during flare-ups can help reduce spread.

Symptoms and Signs to Watch For

Early keratitis often presents with subtle redness and tearing, but as the disease progresses, the signs become hard to miss. Any persistent eye abnormality in a cat warrants a prompt vet visit.

The general symptoms of feline keratitis include:

• Ocular redness and conjunctival inflammation
• Excessive tearing or discharge ranging from watery to mucoid to mucopurulent
• Squinting (blepharospasm) and frequent blinking
• Pawing or rubbing at the affected eye
• Light sensitivity (photophobia), your cat may hide in dark rooms
• Visible cloudiness, color change, or vascularization of the cornea ^{[3, 1]}

In ulcerative keratitis, pain is often pronounced. Cats hold the eye tightly shut, tear copiously, and may show a visible cloudy dent or defect on the corneal surface. Large geographic ulcers can cover a quarter or more of the cornea and are usually accompanied by secondary anterior uveitis (inflammation inside the eye) causing a constricted pupil ^[5].

Non-ulcerative keratitis typically appears as a hazy "misty" cornea, often with new blood vessels creeping across the surface and patches of brown or amber pigment indicating chronicity ^[1].

Eosinophilic keratitis has a particularly distinctive look: raised, irregular pink, white, or tan plaques with a gritty, sometimes calcified texture, usually beginning near the corneal edge (limbus) or third eyelid. The third eyelid and conjunctiva may appear thickened and inflamed ^{[7, 11]}.

Herpetic keratitis tends to produce branching (dendritic) or map-like (geographic) corneal ulcers, often with concurrent conjunctivitis and sometimes mild upper respiratory signs like sneezing or nasal discharge ^{[9, 3, 5]}.

In severe or advanced cases, keratitis can lead to corneal stromal abscesses, rapidly deepening ulcers (descemetoceles), or even full-thickness perforation with iris prolapse. Owners may notice a sudden change in eye shape, intense pain, and possible loss of the eye. Secondary anterior uveitis is common and shows up as a constricted pupil, cloudy aqueous flare, and low intraocular pressure ^{[5, 3]}.

What Can Be Mistaken for Keratitis?

Because several eye diseases can mimic keratitis, accurate diagnosis is essential, the wrong treatment can actually worsen the problem.

The most common confusion is with conjunctivitis, which is inflammation of the pink membrane around the eye without corneal opacity or fluorescein staining (the dye test used to detect ulcers) ^{[2, 3]}. Treating conjunctivitis with steroids when the real issue is herpetic keratitis, for example, can trigger severe viral reactivation.

Corneal sequestrum appears as a dark brown to black discolored patch of cornea that typically develops with long-standing, slow-healing ulcers, often causing significant pain ^[3]. Anterior uveitis without keratitis causes a constricted pupil and cloudy aqueous flare, but the cornea itself stays clear. Glaucoma (elevated eye pressure) can also cause a cloudy cornea due to edema, but the pupil is usually dilated and non-responsive, tonometry (pressure measurement) provides definitive differentiation ^{[1, 2]}.

Keratoconjunctivitis sicca (dry eye) produces chronic mucoid discharge and conjunctival hyperemia, with secondary corneal changes diagnosed via a Schirmer tear test. Corneal endothelial dystrophy causes bilateral, non-painful, progressive corneal clouding in older cats without inflammation or vascularization. Finally, eyelid and third-eyelid masses (including cherry eye, or prolapsed nictitating membrane gland) can resemble proliferative keratitis but leave the cornea clear unless secondary changes develop.

What this means for your cat: If your cat has any cloudy, red, or painful eye, never assume it's "just conjunctivitis." A proper ophthalmic exam, including fluorescein staining, tear testing, and pressure measurement, is the only way to know what's really going on.

How Vets Diagnose Keratitis

Diagnosis of feline keratitis starts with a thorough history, including how the cat has responded to any prior antibiotics or steroids, followed by a complete physical exam and a magnification-aided ophthalmic examination ^{[1, 2]}.

The key diagnostic tests include:

• Fluorescein staining: A drop of bright green dye is applied to the eye; under a blue light, any ulcerated area glows green, revealing the size, depth, and pattern of the lesion ^{[2, 1]}.
• Schirmer tear test: A small paper strip measures tear production to confirm or rule out dry eye as a cause or complicating factor ^{[2, 1]}.
• Tonometry: A specialized device measures intraocular pressure. Low pressure suggests uveitis (often accompanying keratitis), while high pressure points toward glaucoma ^{[2, 1]}.
• Corneal cytology: For suspected eosinophilic keratitis, gentle corneal scraping reveals large numbers of eosinophils and mast cells, a finding considered pathognomonic (uniquely diagnostic) for the disease ^{[6, 11, 10]}.
• PCR testing: Swabs from the cornea or conjunctiva can detect feline herpesvirus-1 DNA, while immunofluorescent antibody (IFA) testing offers a less sensitive alternative ^{[5, 1]}.
• Bacterial and fungal cultures: Indicated when purulent discharge or stromal melting suggests microbial infection ^[5].
• Specialized amoeba testing: For suspected Acanthamoeba keratitis, vets may use in vivo confocal microscopy, non-nutrient agar cultures, and histopathology ^[5].
• Corneal biopsy: May be required for proliferative or atypical lesions to distinguish keratitis from neoplasia when cytology is inconclusive.

Treatment Options for Keratitis in Cats

The right treatment depends entirely on the type and cause of keratitis, there is no single protocol that fits every case.

For simple superficial ulcers, broad-spectrum topical antibiotics (such as oxytetracycline or Terramycin) combined with systemic pain relief (NSAIDs) typically promote healing. If secondary anterior uveitis is present, topical atropine is added to relieve pupillary spasm. Deep, stromal, or infected ulcers require more intensive therapy, often fortified topical antibiotics, anti-collagenase agents (such as autologous serum or EDTA) to prevent stromal melting, and close monitoring or hospitalization. Indolent (non-healing) ulcers may benefit from epithelial debridement, bandage contact lens placement, or grid keratotomy to stimulate re-epithelialization.

For herpetic keratitis, specific antiviral therapy is added: topical cidofovir, trifluridine, or idoxuridine, combined with or without systemic famciclovir, can reduce viral replication and limit recurrence ^{[1, 7, 8]}.

For immune-mediated non-ulcerative keratitis, including pannus and pigmentary keratitis, long-term topical corticosteroids (such as 0.1% dexamethasone) and/or cyclosporine are first-line; systemic steroids or megestrol acetate are reserved for refractory cases ^{[1, 2, 11, 10]}. In eosinophilic keratitis, topical dexamethasone is the cornerstone of therapy, but any corneal ulcer must be fully healed before steroids start. Oral megestrol acetate or cyclosporine are added for recurrent or resistant disease ^{[2, 11, 10, 6]}.

When pigment or scarring has significantly impaired vision, superficial keratectomy (keratotomy) can surgically remove pigmented or opaque tissue, often restoring excellent vision ^[1]. Large or deep ulcers may require surgical intervention, keratectomy with conjunctival grafting provides structural support and enhances healing. For descemetoceles (very deep ulcers threatening perforation), conjunctival flaps, corneal grafts, or amnion grafts can provide tectonic support and prevent catastrophic rupture ^[3].

Addressing the underlying cause is equally critical: entropion repair, removal of ectopic cilia, dry eye management with tear stimulants and artificial tears, and correction of conformational eyelid defects all help break the cycle of chronic keratitis ^{[4, 1]}.

All treatment plans require scheduled re-examinations to monitor healing, adjust medications, and watch for complications such as steroid-induced ocular hypertension ^[1].

New and Emerging Treatments for Feline Keratitis

One of the most exciting developments in feline eye care is the use of mesenchymal stem cell (MSC) therapy for treatment-resistant eosinophilic keratitis ^{[10, 6]}.

In a pilot study, all five cats with chronic, treatment-refractory FEK received two subconjunctival implantations of allogeneic (donor-matched) feline adipose-derived mesenchymal stromal cells (fAd-MSCs), 2 months apart. The result: progressive resolution of corneal plaques, vascularization, and hyperemia, with negative corneal cytology for eosinophils and mast cells at follow-up. Clinical remission was achieved within 2–6 months ^[6].

What this means for your cat: MSC therapy offers a potentially safer long-term alternative to corticosteroids or megestrol acetate, both of which carry serious risks including diabetes mellitus, adrenal suppression, and mammary neoplasia ^[6].

Other emerging approaches include topical interferon for viral keratitis (variable efficacy), ganciclovir ophthalmic gel (not yet evaluated in cats), and corneal cross-linking for infectious keratitis (still investigational) ^[8]. The feline Acanthamoeba keratitis model itself serves as a translational research platform, meaning insights from cat studies may inform new anti-amoebic drugs for both feline and human patients ^[5].

What Happens if Keratitis Is Left Untreated?

Untreated keratitis is a vision-threatening emergency. The longer it persists, the higher the risk of permanent damage, including blindness and loss of the eye itself.

Ulcerative keratitis can deepen rapidly from a simple superficial ulcer to a descemetocele or full-thickness perforation, allowing intraocular infection (endophthalmitis) and risking globe loss. Long-standing ulcers may also develop a corneal sequestrum, a painful, dead patch of cornea that contributes to vision loss ^[3].

Chronic non-ulcerative keratitis leads to permanent corneal pigmentation, dense vascularization, and stromal scarring that physically blocks light, often resulting in irreversible vision impairment ^[1].

Eosinophilic keratitis never resolves spontaneously, without treatment, the gritty plaques enlarge and may cover the entire corneal surface, causing persistent pain, vision loss, and bilateral involvement ^{[6, 10]}.

Herpetic keratitis, if unmanaged, drives recurrent painful episodes, progressive stromal scarring, symblepharon (adhesion of conjunctiva to cornea), and eventual blindness ^{[9, 3]}. In many long-standing or deep cases, surgical intervention such as keratectomy with conjunctival grafting becomes necessary to save the eye ^[3].

Long-Term Management and Living With Keratitis

For most chronic forms of feline keratitis, particularly eosinophilic keratitis and other immune-mediated types, lifelong management is the rule rather than the exception. The goal is to control inflammation with the lowest effective medication dose.

Routine rechecks are essential. Initially every few weeks, then every 3–6 months, vet visits allow monitoring of corneal clarity, intraocular pressure, tear production, and early detection of medication side effects ^[1].

For FHV-1-associated keratitis, stress reduction is critical. Stable routines, environmental enrichment, and minimizing multi-cat conflict can all reduce viral reactivations. Some cats benefit from long-term low-dose oral famciclovir to reduce flare frequency.

Owner education plays a huge role. Learning to recognize early relapse signs, increased squinting, renewed cloudiness, new plaque formation, allows prompt veterinary reassessment before disease progresses.

For cats with permanent corneal scarring or pigmentation, partial vision loss is common, but cats adapt remarkably well when their home environment stays consistent. Keep food, water, litter boxes, and resting spots in predictable places, and avoid moving furniture.

Periodic Schirmer tear tests and fluorescein exams help detect concurrent dry eye or recurrent ulceration, both common long-term complications of chronic keratitis and its treatment ^[1].

Prognosis and Outlook

The prognosis for feline keratitis varies widely, from excellent for simple ulcers to guarded for chronic immune-mediated disease.

• Uncomplicated bacterial or traumatic ulcers carry an excellent prognosis with prompt treatment and removal of the underlying cause, most cats achieve full corneal healing and restored vision ^[3].
• Herpetic keratitis has a more guarded long-term outlook due to viral latency and recurrence, but consistent antiviral therapy can significantly reduce flare frequency and severity ^{[9, 3]}.
• Eosinophilic keratitis is typically controllable but not curable. With consistent treatment, most cats maintain comfortable vision, though relapses are common when medications are tapered too quickly or stopped ^{[2, 10]}.
• Pigmentary keratitis managed with keratectomy carries an excellent prognosis for visual recovery, provided the underlying irritant is resolved ^[1].
• Deep stromal ulcers or descemetoceles requiring surgery generally carry a fair to good prognosis when treated early by a veterinary ophthalmologist, though enucleation (eye removal) may be necessary if perforation or endophthalmitis occurs.

In experimental feline Acanthamoeba keratitis, outcomes vary, some cats develop persistent stromal abscesses while others have only mild infiltrates, but whether this replicates chronic human disease remains unknown ^[5].

The single most important factor in prognosis across all keratitis types is early detection and appropriate intervention. Cats treated promptly do dramatically better than those who wait.

What We Still Don't Know: Gaps and Current Research

Despite decades of research, several critical questions about feline keratitis remain unanswered.

The exact antigenic trigger for eosinophilic keratitis is still unknown, it's unclear whether it represents a primary allergic reaction, an immune response to FHV-1 antigens, or something else entirely ^{[7, 6, 10]}. The association between FHV-1 and FEK is strong (up to 75% co-occurrence in some studies), but a direct causative mechanism has not been established, and antiviral therapy alone often fails to resolve the disease ^[7].

Optimal topical corticosteroid tapering protocols for eosinophilic keratitis have not been standardized, and no large-scale controlled trials have directly compared long-term outcomes of different immunosuppressive regimens.

L-lysine has been widely used for FHV-1 management, but studies have shown variable efficacy, and large controlled clinical trials are still needed ^{[8, 9]}.

Subconjunctival MSC implantation has shown encouraging results in a small pilot study of refractory FEK, but large, randomized controlled trials are needed to confirm long-term safety and efficacy ^[10].,

The true prevalence of naturally occurring Acanthamoeba keratitis in cats is unknown and likely underdiagnosed because specific testing is not routinely performed; diagnostic criteria and optimal treatment protocols remain poorly defined. Ganciclovir and other nucleoside analogue antivirals have not been evaluated in vivo in cats for herpetic keratitis, leaving a gap in our understanding of their safety and corneal penetration ^[8].

Finally, ocular microbiome and biofilm interactions in eosinophilic keratitis, and the use of MSC-derived exosomes for corneal regeneration, are under investigation but have not yet reached clinical application.

What this means for your cat: Research is moving quickly. If your cat has treatment-resistant keratitis, ask your vet about clinical trials or specialist referral, emerging therapies like stem cell implantation may be available in academic or referral settings.

❓ Frequently Asked Questions