Bit & Bridle

Equine Keratitis

Other Names

  • Corneal keratitis
  • Ulcerative keratitis (when involving corneal ulceration)
  • Non-ulcerative keratitis (immune-mediated or stromal)
  • Infectious keratitis (bacterial or fungal)
  • Corneal disease

What is Equine Keratitis?

Keratitis is inflammation of the cornea — the transparent, dome-shaped structure forming the front of the eye. It is a significant and frequently encountered ocular condition in horses and, without prompt and appropriate treatment, can cause permanent corneal scarring, vision impairment, or even loss of the eye. Horses have large, prominent eyes that are particularly vulnerable to trauma and environmental insults, making keratitis more common in equines than in many other species.

The cornea is avascular — it has no blood vessels under normal circumstances — which means it relies entirely on the tear film, aqueous humour, and atmospheric oxygen for nutrition. This makes it susceptible to rapid deterioration when inflamed, infected, or damaged, as the normal vascular healing response is absent. Corneal vascularisation (blood vessel ingrowth) is actually a sign of chronic or severe disease.

Keratitis can be ulcerative (involving a break in the corneal epithelium) or non-ulcerative. Ulcerative keratitis carries a greater immediate risk and must be treated as a veterinary emergency. For related equine eye conditions, see our entries on Equine Cataracts and equine recurrent uveitis.

Causes

Keratitis in horses results from a range of causes, which can be broadly categorised as follows:

  • Trauma and foreign bodies — the most common initiating cause. Brambles, hay seeds, wood splinters, flies, or blunt trauma can abrade or penetrate the corneal surface, creating an entry point for infectious organisms
  • Bacterial infection — organisms such as Pseudomonas aeruginosa, Staphylococcus spp., Streptococcus spp., and Bacillus spp. are commonly isolated from infected corneal ulcers. Bacteria can colonise traumatic lesions rapidly, leading to progressive, melting (collagenolytic) ulcers in severe cases.
  • Fungal infection (keratomycosis) — Aspergillus, Fusarium, and other fungi can cause deep, aggressive corneal infections, often following trauma with plant material. Fungal keratitis tends to progress slowly but is difficult to treat and can be sight-threatening.
  • Viral infection — equine herpesvirus-2 (EHV-2) has been associated with superficial punctate keratitis in horses; equine influenza can occasionally cause mild corneal involvement
  • Immune-mediated keratitis — non-infectious, stromal keratitis driven by the horse’s own immune response; often associated with equine recurrent uveitis (ERU). Presents as diffuse or focal corneal opacity without ulceration.
  • Exposure keratitis — in horses with facial nerve palsy (inability to blink), the cornea is inadequately protected and dries out, leading to desiccation and inflammation
  • Corneal oedema — secondary to uveitis or other intraocular disease; corneal oedema appears as a blue-white haziness and indicates compromised corneal endothelial function

Symptoms and Signs

Clinical signs of keratitis vary with the cause and severity but typically include:

  • Ocular pain — blepharospasm (squinting), photophobia (sensitivity to light), and excessive tearing (epiphora)
  • Visible corneal opacity — white, grey, yellow, or cloudy areas on the normally clear cornea
  • Corneal vascularisation — pink or red blood vessels growing across the surface or into the stroma; indicates chronicity
  • Mucopurulent ocular discharge
  • Corneal ulceration — a defect in the corneal epithelium, which may be stained green with fluorescein dye by the vet
  • Swelling of the eyelids
  • Hypopyon — white or yellow fluid (pus) visible at the bottom of the anterior chamber of the eye in severe cases
  • Miosis — the pupil may be constricted if there is associated uveitis

Any horse showing ocular pain, squinting, tearing, or a visible abnormality of the eye surface should be examined by a vet promptly — delay significantly worsens the prognosis for severe cases.

Diagnosis

Thorough ophthalmic examination is essential and should ideally be performed with pharmacological sedation and, if necessary, a local anaesthetic eye drop to reduce blepharospasm:

  • Fluorescein staining — a fluorescent dye that adheres to exposed corneal stroma wherever the epithelium is absent. The eye is illuminated with a blue light — any ulcerated area fluoresces bright green. Essential for all suspected corneal ulcers.
  • Slit-lamp biomicroscopy — detailed examination of the corneal layers to assess depth of the lesion, stromal involvement, and any anterior chamber changes
  • Corneal scraping and culture — swabs or scrapings from the ulcer margin should be submitted for bacterial and fungal culture and sensitivity before antibiotic treatment begins. This is critical for guiding appropriate antibiotic choice, particularly for deep or non-responsive ulcers.
  • Cytology — impression smears or scrapings examined microscopically can reveal the organism type, hyphal elements (suggesting fungi), or inflammatory cell patterns
  • Tonometry — measurement of intraocular pressure to detect concurrent uveitis (which typically causes low IOP) or secondary glaucoma (high IOP)

Treatment

Treatment of equine keratitis is intensive and requires commitment from the owner, as frequent application of topical medications is the norm:

  • Topical antibiotics — broad-spectrum antibiotic eye drops (oxytetracycline, chloramphenicol, ciprofloxacin, or gentamicin) are the mainstay of bacterial keratitis treatment. Frequency varies from every one to four hours depending on severity.
  • Topical antifungals — natamycin, voriconazole, or miconazole for fungal keratitis. Antifungal treatment must be prolonged and consistent — fungal keratitis is slow to respond.
  • Atropine — applied topically to dilate the pupil and relieve the spasm of the ciliary muscle that causes pain with uveitis. Also reduces the risk of posterior synechia (adhesion of iris to lens).
  • Anti-proteases — topical acetylcysteine or EDTA are used in “melting” ulcers where collagenolytic enzymes are causing rapid corneal dissolution. These prevent further stromal destruction.
  • NSAIDs — systemic and/or topical NSAIDs reduce inflammation and pain
  • Subpalpebral lavage (SPL) system — a thin tube is placed under the upper eyelid and tunnelled to the headcollar or mane, allowing frequent medication delivery without the need to approach the eye directly. Invaluable for horses that are fractious about eye treatment or require hourly medication.
  • Surgical options — conjunctival flap surgery, corneal grafting, or keratectomy may be required for deep, non-responsive, or perforated corneal ulcers. Referral to a specialist equine ophthalmologist is recommended for severe cases.
  • Protective care — a fly mask or protective eye hood should be worn to reduce further trauma and UV exposure

For equine ophthalmic referral services in the UK, your vet can advise on local specialist centres. The BEVA also maintains a list of equine specialist practitioners at beva.org.uk.

Prevention

Preventive measures reduce the frequency and severity of corneal injuries:

  • Use a fly mask with UV protection during turnout — this reduces fly-mediated eye irritation and physical trauma from vegetation
  • Manage pasture vegetation — trim plants and branches to below eye level; remove brambles and thorny plants near field boundaries
  • Inspect horses’ eyes daily — early detection of redness, discharge, or squinting allows prompt treatment before minor lesions progress
  • Ensure stabling environments are free from sharp protrusions at eye height
  • Apply fly repellent around the face to reduce insect pressure on the eyes

Prognosis

The prognosis for equine keratitis varies widely. Superficial, uncomplicated ulcers with prompt appropriate treatment generally heal well with minimal scarring. Deep stromal ulcers, infected ulcers (particularly fungal), and those approaching or involving corneal perforation carry a significantly more guarded prognosis and may result in permanent corneal scarring, vision loss, or loss of the eye (enucleation) in the worst cases. Early veterinary intervention is the single most important prognostic factor.

When to Call the Vet

  • Your horse is squinting, has a watery or discharging eye, or is clearly in ocular discomfort
  • You can see any cloudiness, opacity, or visible lesion on the surface of the eye
  • Your horse’s eye appears sunken, very red, or the pupil looks abnormal
  • A corneal ulcer that was improving appears to be worsening or “melting”
  • You are finding it difficult to administer medication into the eye and treatment is falling behind schedule

Frequently Asked Questions

How serious is a corneal ulcer in a horse?

The seriousness depends on the depth, size, cause, and rate of progression. Superficial ulcers in healthy eyes can heal within days with appropriate treatment. Deep ulcers, particularly those infected with bacteria (especially Pseudomonas) or fungi, can progress to full-thickness perforation within days to hours in some cases. Any corneal ulcer should be treated as a veterinary emergency until assessed — the window for saving the eye in severe cases can be very narrow.

What is a “melting” corneal ulcer?

A melting ulcer, or keratomalacia, occurs when collagenolytic enzymes — produced by bacteria (particularly Pseudomonas aeruginosa) or released by the horse’s own inflammatory cells — rapidly destroy the collagen matrix of the corneal stroma. The cornea takes on a gelatinous, “melting” appearance and can progress to perforation within hours. Treatment with anti-proteases (acetylcysteine, EDTA) is essential, alongside appropriate antimicrobials. This is an ocular emergency requiring immediate veterinary attention.

Why does my horse need eye drops every two hours?

The horse’s nasolacrimal drainage system and the tear film dilute and remove topical medications relatively quickly. For severe keratitis, particularly fungal or melting ulcers, very frequent dosing is required to maintain therapeutic drug levels at the corneal surface. A subpalpebral lavage (SPL) system is often placed to make this manageable — it allows medication to be administered via a tube without approaching the horse’s eye directly.

What is equine recurrent uveitis, and how does it relate to keratitis?

Equine recurrent uveitis (ERU) is the most common cause of blindness in horses worldwide. It involves repeated episodes of intraocular inflammation that cause progressive damage to the internal eye structures. Keratitis (corneal inflammation) and cataracts can both develop as secondary complications of ERU. Horses with ERU require ongoing management to reduce the frequency and severity of uveitis episodes and protect the remaining visual structures. See our equine eye terminology guide for more.