The Tube in the Tack Trunk

Every hunter/jumper barn keeps some version of the same shelf: fly spray, a roll of vet wrap gone slightly grey at the edges, and, toward the back, a half-used tube of antibiotic ointment kept for exactly one purpose — the morning a horse comes in from turnout with one eye squeezed shut. The instinct that follows is close to universal and rarely examined: apply the ointment, watch it overnight, call the vet if it hasn't cleared by morning. That habit was built on decades of the ointment working. New research on antimicrobial resistance in equine eye infections says it can no longer be trusted to hold, and that the horses most exposed are exactly the ones on the show circuit.

Why a Horse's Eye Fails Differently

A scratched cornea is one of the most routine calls an equine vet takes, and one of the least routine problems a horse actually has. Data drawn from the Veterinary Medical Database and from the University of Tennessee's ophthalmology caseload, published by researchers Erica Tolar and Diane Hendrix, found that ulcerative keratitis accounted for roughly 18 percent of all equine ocular disease recorded between 1980 and 1993, about 24 percent of the ophthalmic patients the university has seen since, and as much as 85 percent of the equine ophthalmic cases serious enough to require hospitalization. The horse's eye is simply built to get hurt: it is large, positioned for a wide field of view rather than protection, and set on an animal that puts its face into hay nets, fence lines, trailer dividers and each other's teeth all day. What makes it different from a dog's or a cat's scratched cornea is what happens next. Horses are more prone than other domestic species to secondary bacterial infection of a corneal wound, and once bacteria take hold, the clock that matters is measured in hours, not days.

The tube in the tack trunk was never keeping pace with that clock so much as getting lucky with it.

The Reflex That's Losing Its Match

A 2026 review in the journal Veterinary Ophthalmology by Lionel Sebbag and Oren Pe'er of the Hebrew University of Jerusalem's Koret School of Veterinary Medicine examined the antimicrobial resistance data now accumulating across companion and sport animal ophthalmology, horses included. The pathogens turning up most often on culture — Staphylococcus pseudintermedius, beta-hemolytic streptococci and Pseudomonas aeruginosa — are not new. What has shifted is how many of those isolates no longer respond to the antibiotics that used to handle them, with the heaviest burden of multidrug resistance concentrated in referral-hospital populations and among methicillin-resistant staphylococci. In practice, that means the horses arriving at a referral ophthalmologist after a few days of field or barn treatment are disproportionately the ones now carrying the hardest infections to clear.

A separate study from the University of Tennessee Veterinary Medical Center, led by researcher K. Foote and published in Equine Veterinary Education, compared bacterial isolates taken from horses with ulcerative keratitis between 2011 and 2020 against the university's own published data from 1993 to 2004. Streptococcus, Staphylococcus and Pseudomonas remained the dominant genera, at 35, 29 and 13 percent of the 31 isolates cultured, but the balance among them had moved — more Staphylococcus, less Streptococcus, than the earlier decade recorded. The specific antibiotic a vet reaches for first, in other words, is being chosen against a bacterial population that keeps rearranging itself underneath the old assumptions.

What "Melting" Actually Means

The reason the steroid warning is not a formality: an eye ointment containing a corticosteroid can be exactly the right call once a vet has confirmed there is no active infection, and exactly the wrong one if there is. On an infected ulcer, a steroid suppresses the eye's own defense and can accelerate a process vets call a melting cornea, in which the corneal tissue itself begins to break down. Pseudomonas is the pathogen most associated with this outcome; it is, according to the referral ophthalmology literature at UC Davis, the most commonly devastating organism cultured from equine bacterial keratitis because of its tendency to trigger this kind of rapid tissue breakdown and, in the worst cases, corneal perforation. That is not a sore eye. That is a horse's sight and, quite possibly, a horse's career, decided inside a window of hours. Colorado State University's Veterinary Teaching Hospital states the standard for its own field service in six words: "An abnormal horse eye is always an emergency."

Where the Field Is Actually Moving

The response to rising resistance in equine medicine, as in human medicine, has not been to abandon antibiotics but to use them more precisely, and to look for ways to treat without them at all where possible. A 2026 study out of the University of Veterinary Medicine Hannover, led by Leonie Stolle and Claudia Busse in the ophthalmology service there, tested three non-antibiotic antiseptics — polyhexanide, povidone-iodine and hypochlorous acid — against the bacteria most commonly cultured from equine ulcerative keratitis and found all three showed strong antimicrobial activity at low concentrations in vitro. It is early, laboratory-stage evidence, not a replacement for culture-guided antibiotic therapy in an active infection. But it points at the direction equine ophthalmology is heading: toward stewardship, toward saving the strongest antibiotics for when nothing else will work, rather than toward the first tube on the shelf.

That direction runs against a second, newer reflex working in the opposite one. Data from the RSPCA's Animal Kindness Index published this year found that roughly one in ten pet owners now routinely turns to an AI chatbot for advice on an animal's health, most often to check symptoms, before ever calling a professional. A horse's eye is a poor place to test that habit. It is not a diagnosis that improves with a second opinion from a language model at eleven at night; it is a physical exam, a stain, and in the cases that call for it, a culture read by someone trained to interpret it.

None of this asks a barn to panic over every weepy eye after a windy turnout day — most corneal scratches remain exactly what they have always been, minor and quick to heal under proper care. It asks for the reflex to change. The tube in the tack trunk earned its place there over years of working well enough, often enough, that nobody thought to question it. The research this year is the question. A horse built to compete at the level this sport asks of it does not get a second eye if the first guess is wrong.