Ophthalmology

Resistance making eye infections harder to treat

Sight-threatening eye infections in horses and other companion animals are becoming more difficult to treat as antibiotic-resistant bacteria spread worldwide, according to a recent review by researchers from the Hebrew University of Jerusalem (Vet
Ophthalmol 2026;29[4]:e70209).

The review by Lionel Sebbag, DVM, PhD, DACVO, and Oren Pe’er, DVM, AICVO, ECVO, of the Koret School of Veterinary Medicine, Hebrew University of Jerusalem, examined the growing challenge of antimicrobial resistance (AMR) in veterinary ophthalmology, focusing on bacterial corneal infections that can threaten vision within hours or days if left uncontrolled.

Bacterial keratitis is among the most urgent emergencies in veterinary eye care, they said. While antibiotics remain the cornerstone of treatment, the researchers found mounting evidence that many of the bacteria responsible for these infections are becoming increasingly resistant to commonly used drugs.

Drawing on studies from North America, Europe, Asia, South America and Australia, the review identifies Staphylococcus pseudintermedius, beta-hemolytic streptococci and Pseudomonas aeruginosa as the most frequently isolated bacterial pathogens in companion animals. Particularly concerning is the rising prevalence of multidrug-resistant strains, especially in referral and specialty-care settings where the most severe cases are concentrated.

One of the most consistent findings across the studies was the effect of previous antibiotic use. Animals that had recently received topical antimicrobial treatment were more likely to harbor resistant bacteria and less likely to yield positive culture results, making accurate diagnosis and targeted treatment more challenging.

The review also highlighted a surprising gap between laboratory testing and real-world clinical outcomes. Standard antimicrobial susceptibility tests are based largely on how antibiotics behave when administered systemically, yet eye drops achieve different drug concentrations at the ocular surface. As a result, laboratory susceptibility reports may not always accurately predict whether a treatment will succeed or fail in clinical practice, according to the veterinarians.

The authors said resistance is no longer “a theoretical concern in veterinary ophthalmology.” Instead, it is a clinical reality for today’s practitioners.

The researchers argued that laboratory findings should always be interpreted alongside clinical observations, disease severity, and patient history. They emphasize the importance of obtaining microbiological samples before extensive antibiotic treatment whenever possible, allowing veterinarians to make more informed treatment decisions.

Beyond the immediate clinical implications, the review places antibiotic-resistant eye infections within a broader One Health framework. Some bacterial species commonly found in animal eye infections have recognized zoonotic potential.

The authors noted that veterinary clinics, equipment and even households can serve as environments where resistant organisms circulate, highlighting the importance of rigorous hygiene and infection-control practices.

Looking ahead, the review explored a range of antibiotic-sparing approaches designed to reduce reliance on traditional antimicrobials. These include antiseptic therapies, biofilm-disrupting treatments, corneal cross-linking technologies, ultraviolet-based approaches and other emerging methods that may complement conventional antibiotic therapy.

The authors concluded that preserving the effectiveness of existing antibiotics will require coordinated efforts in surveillance, antimicrobial stewardship, infection control and the development of ophthalmology-specific guidelines for managing ocular infections.

“The goal is not simply to resolve the current infection,” the authors write, “but to preserve therapeutic reliability for future patients.” MeV