Fungal Keratitis in Horses

Fungal keratitis is an infection and inflammation of the cornea, the clear front surface of the eye. In horses, this problem is often called equine keratomycosis. It is considered an eye emergency because the cornea can weaken, deepen, and even perforate in a short time if treatment is delayed.

Horses are more vulnerable to fungal corneal disease than many other species. Fungi are common in the equine environment and around the eye, so when the corneal surface is scratched or otherwise damaged, organisms can gain access to deeper tissue. Merck notes that fungal keratitis is predominantly a problem in horses, and complicated corneal ulcers in horses are treated with an antifungal because of this risk.

This condition can look dramatic, but early care matters more than appearance alone. Some horses develop a dense white plaque, corneal swelling, new blood vessels growing into the cornea, or a painful "melting" ulcer. Even when vision can be saved, treatment is often intensive and may require medication many times a day.

For pet parents, the most important takeaway is speed. A horse with a suddenly painful, cloudy, or ulcerated eye needs prompt veterinary attention, because fungal keratitis can progress faster than many people expect.

Fungal keratitis usually starts when the cornea loses its normal protective barrier. A small scratch from hay, bedding, dust, a branch, or another source of plant material can be enough to let fungi colonize the cornea. Horses live in environments where fungal organisms are common, so even a minor injury can become a bigger problem.

Complicated corneal ulcers are a major setup for fungal infection. Merck notes that if stromal loss, infiltrate, or corneal malacia is present, your vet should investigate the cause with cytology and bacterial and fungal culture. In practice, fungal keratitis is often suspected when a corneal ulcer is not healing as expected, develops a white plaque, or becomes more painful.

Common fungal genera reported in equine keratitis include Aspergillus and Fusarium, though other fungi can be involved. Prior topical corticosteroid use, delayed treatment, and prolonged ulcer disease may increase risk by weakening local defenses or masking progression.

Not every painful eye is fungal, and not every corneal ulcer becomes infected with fungus. That is why direct examination, staining, and sampling matter. Your vet will help determine whether the problem is fungal, bacterial, mixed, or noninfectious, because treatment choices differ in important ways.

Diagnosis starts with a careful eye exam. Your vet will usually assess pain, eyelid swelling, discharge, corneal clarity, and whether the horse has reflex uveitis. A fluorescein stain is commonly used to look for an ulcer, although some deeper stromal abscesses may not retain stain if the surface has already healed over.

For suspected infectious keratitis, Merck recommends corneal cytology and bacterial and fungal culture when stromal loss, infiltrate, or malacia is present. Cytology can sometimes reveal branching fungal hyphae quickly, while culture helps identify the organism and guide treatment. Because fungi can also be present in the environment around the eye, sample collection technique matters.

Some referral hospitals use additional tools when the diagnosis is unclear or time is critical. Cornell reports that in vivo confocal microscopy can provide immediate, noninvasive imaging of the cornea and has been used to diagnose fungal keratitis in horses faster than waiting for traditional culture results, which may take 10 to 14 days.

Your vet may also recommend referral if the ulcer is deep, rapidly progressive, or threatening to perforate. That is not a sign you waited too long. It often means the eye needs specialized imaging, a subpalpebral lavage system, microsurgery, or more intensive monitoring to give the horse the best chance of comfort and vision.

You cannot prevent every eye injury, but you can lower risk. Prompt attention to any squinting, tearing, or cloudy eye is one of the most practical steps. Early treatment of a simple corneal ulcer may help prevent it from becoming a complicated infected ulcer.

Reduce avoidable eye trauma where possible. Check stalls, fencing, feeders, and turnout areas for sharp edges or protruding plant material. During dusty seasons or when flies are heavy, some horses benefit from a well-fitted fly mask, especially if they are prone to eye irritation.

Avoid using leftover eye medications unless your vet tells you to. This is especially important with steroid-containing eye products, because steroids can worsen some corneal infections and delay healing. If your horse has a known ulcer or a painful eye, your vet should guide every medication choice.

Finally, keep follow-up appointments. Horses with corneal ulcers can change quickly, and Merck emphasizes frequent reassessment for equine corneal disease. Prevention is not only about avoiding the first injury. It is also about catching a worsening ulcer before fungal infection causes deeper damage.