Efficacy of Therapeutic UVC Irradiation in Reducing Bacterial Load in Microbial Keratitis: A Retrospective Clinical Study in Veterinary Patients.

A single low-dose UVC exposure reduced corneal bacterial load by over 96% in veterinary microbial keratitis cases.

This retrospective clinical study evaluated the immediate antimicrobial efficacy of a single low-dose therapeutic ultraviolet-C (UVC) irradiation on corneal bacterial load in veterinary patients diagnosed with microbial keratitis (MK). Thirty-four eyes from 30 client-owned patients (25 dogs, 6 horses, 3 cats) were treated at a UK referral ophthalmology clinic in 2025. Each eye received one 5-second UVC exposure at 265 nm (fluence 17.5 mJ/cm²) using a commercially available device (PhotonUVC). Paired corneal swabs collected immediately before and after treatment were cultured for colony-forming unit (CFU) quantification. Results demonstrated a median CFU reduction from 89.5 pre-treatment to 15.0 post-treatment, representing a median percent reduction of 96.5% (mean 92.3 ± 9.6%). Notably, 32 of 34 eyes (94%) achieved at least 75% bacterial reduction, and 11 eyes (32%) became culture-negative following a single exposure. Efficacy was observed across a broad spectrum of clinically relevant pathogens including Staphylococcus, Streptococcus, Pseudomonas, and coliforms, spanning all three species groups. While this study demonstrates a compelling immediate bactericidal effect, its retrospective, uncontrolled design and small sample size limit definitive conclusions. No long-term outcomes or adverse effects were reported. The authors recommend prospective controlled trials to clarify UVC's role as an adjunct to conventional antimicrobial therapy in veterinary ophthalmology practice.

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