Ultraviolet C (UV-C) Light Therapy for Equine Ulcerative Keratomycosis—An In Vitro Study

Objectives: To assess if an affordable, commercially available 275 nm ultraviolet C (UV-C) device can inhibit fungal pathogens associated with equine keratomycosis and to establish the optimal exposure time/dose required in vitro. Methods: Fungal inhibition zone surface areas of isolates from two fungal genera (Aspergillus and Fusarium spp.) were compared in triplicates after UV-C exposure at distances of 10, 15, and 20 mm with single or repeat doses (4 h apart) of 5, 10, 15, or 30 s duration after 24, 48, and 72 h of incubation. Inhibition zones were microscopically assessed, and regrowth checks were performed. Results: Fungal inhibition was achieved with the lowest exposures/doses of 5 s/7.5 mJ/cm2 and 10 s/7 mJ/cm2 at distances of 10 and 20 mm, respectively. At 10 mm, the fungal inhibition zone was statistically significantly enlarged by increasing exposure/dose from 5 s to 15 s/22.5 mJ/cm2 for all isolates. Only Aspergillus flavus showed a further significant zone enlargement after a 30 s/45 mJ/cm2 exposure/dose. Fungal inhibition zone sizes did not differ significantly between isolates after 15 s exposure regardless of distance, but an increased distance led to a subjective increase in fungal regrowth. While inhibition zones decreased over time, no central growth was noted despite the lack of complete fungal eradication. Conclusions: For Aspergillus and Fusarium spp., an exposure/dose of 15 s at a 10 mm distance/22.5 mJ/cm2 may optimally align antifungal efficacy with previously reported corneal safety data. Further preclinical and safety studies are required to ensure that this effect translates into clinical practice.