Veterinary ophthalmology2026; 29(5); e70230; doi: 10.1111/vop.70230

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

Dixon, CJ
·
Lewin, GA

Abstract: To evaluate the immediate effect of therapeutic ultraviolet-C (UVC) irradiation on corneal bacterial load in veterinary patients with microbial keratitis (MK), using a retrospective analysis of clinical data collected at a UK referral ophthalmology hospital. Methods: Client-owned dogs, horses, and cats presented to a referral ophthalmology clinic with MK in 2025. Methods: Clinical records from MK cases were reviewed. For each case, paired corneal swabs were obtained immediately before and immediately after UVC irradiation with a commercially available 265 nm device (PhotonUVC). Treatment consisted of a single 5-s exposure at 3.5 mW/cm (fluence 17.5 mJ/cm). Bacterial colony-forming units (CFU) were quantified by culture. The primary outcome was the percent reduction in CFU; secondary outcomes included proportion of culture-negative results after UVC, laterality (right eye (OD) vs. left eye (OS)), and species subgroup comparisons. Results: A total of 34 eyes from 30 patients (25 canine, 6 equine, 3 feline) met the inclusion criteria. Median (IQR) CFU decreased from 89.5 (30.3-14 400) pre-UVC to 15 (0-207) post-UVC. Median percent reduction was 96.5% (88.5-100.0%); mean 92.3 ± 9.6%. A total of 11 of 34 eyes (32%) were culture-negative after UVC, and 32/34 (94%) showed ≥ 75% reduction. Reductions were observed across all major pathogens, including Staphylococcus, Streptococcus, Pseudomonas, and coliforms. Conclusions: In this cohort of patients, a single low-dose UVC exposure produced substantial immediate reductions in corneal bacterial load in veterinary MK patients. These findings support further controlled trials to define the role of UVC as an adjunct to conventional antimicrobial therapy.

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Publication Date: 2026-07-14 PubMed ID: 42444511PubMed Central: PMC13366281DOI: 10.1111/vop.70230Google Scholar: Lookup

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Summary
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Affiliations
MeSH
Conflict of Interest
References
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Journal Article

Summary

This research summary has been generated with artificial intelligence and may contain errors and omissions. Refer to the original study to confirm details provided. Submit correction.

Research Overview

This study investigated how effective ultraviolet-C (UVC) light treatment is at quickly reducing bacterial infections on the corneas of animals with microbial keratitis.
Using clinical data from veterinary patients, the researchers measured bacterial loads before and after a brief UVC treatment to determine its immediate impact.

Purpose and Objective

To evaluate the immediate antibacterial effect of therapeutic UVC irradiation on corneas infected with microbial keratitis (MK) in veterinary patients.
To quantify changes in bacterial colony-forming units (CFU) before and after UVC exposure.
To explore variations in efficacy across different animal species (dogs, horses, cats) and bacterial types.

Methods

Study design: Retrospective clinical review using data from cases seen at a UK referral ophthalmology hospital in 2025.
Subjects: 30 patients consisting of 25 dogs, 6 horses, and 3 cats diagnosed with microbial keratitis.
Intervention: Each infected eye received a single 5-second exposure to UVC light at 265 nm wavelength, using a commercial device (PhotonUVC) delivering 3.5 mW/cm² (fluence of 17.5 mJ/cm²).
Data collection: Paired corneal swabs were taken immediately before and after UVC treatment.
Outcome measures:
- Primary – Percent reduction in bacterial colony-forming units (CFU) grown from culture.
- Secondary – Percentage of cases becoming culture-negative post-treatment, differences between right (OD) and left (OS) eyes, and bacterial species subgroup analysis.

Results

Sample size: Data from 34 eyes across 30 patients met inclusion criteria.
Reduction in bacterial load:
- Median CFU dropped significantly from 89.5 (interquartile range [IQR] 30.3 to 14,400) before UVC to 15 (IQR 0 to 207) after treatment.
- Median percent reduction in CFU was 96.5% (IQR 88.5% to 100%), with a mean value of 92.3% ± 9.6%.
Culture-negative outcomes: 11 out of 34 eyes (32%) showed no detectable bacterial growth post-UVC.
High efficacy rate: 94% of eyes had at least a 75% reduction in bacterial load.
Effectiveness was consistent across major bacterial pathogens implicated in keratitis, such as Staphylococcus, Streptococcus, Pseudomonas, and coliform bacteria.

Conclusions and Implications

A single, low-dose UVC exposure significantly and immediately reduces bacterial contamination on infected corneas in veterinary patients with microbial keratitis.
UVC treatment demonstrated broad-spectrum activity against common bacterial pathogens associated with MK in animals.
These results justify further controlled clinical trials to explore UVC as a supplementary treatment alongside standard antimicrobial therapies.
Potential benefits of UVC include rapid reduction of bacterial load, which may improve therapeutic outcomes and reduce reliance on antibiotics.

Additional Notes

This study is retrospective and observational, limiting causal inferences.
Immediate effects were measured, but longer-term efficacy and safety were not assessed here.
The UVC dosage was carefully controlled to balance efficacy with safety for corneal tissue.
Future research should include randomized controlled trials and evaluation of clinical healing outcomes following UVC treatment.

Cite This Article

APA

Dixon CJ, Lewin GA. (2026). Efficacy of Therapeutic UVC Irradiation in Reducing Bacterial Load in Microbial Keratitis: A Retrospective Clinical Study in Veterinary Patients. Vet Ophthalmol, 29(5), e70230. https://doi.org/10.1111/vop.70230

Publication

Veterinary ophthalmology

ISSN: 1463-5224

NlmUniqueID: 100887377

Country: England

Language: English

Volume: 29

Issue: 5

Pages: e70230

PII: e70230

Researcher Affiliations

Dixon, Christopher J

Veterinary Vision, Penrith, UK.

Lewin, Gary A

Veterinary Vision, Penrith, UK.

MeSH Terms

Animals
Retrospective Studies
Cats
Dogs
Keratitis / veterinary
Keratitis / radiotherapy
Keratitis / microbiology
Cat Diseases / radiotherapy
Cat Diseases / microbiology
Horses
Ultraviolet Therapy / veterinary
Eye Infections, Bacterial / veterinary
Eye Infections, Bacterial / radiotherapy
Eye Infections, Bacterial / microbiology
Dog Diseases / radiotherapy
Dog Diseases / microbiology
Female
Ultraviolet Rays
Bacterial Load / veterinary
Bacterial Load / radiation effects
Horse Diseases / radiotherapy
Horse Diseases / microbiology
Male

Conflict of Interest Statement

The authors declare no conflicts of interest.

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