Comparison of antimicrobial efficacy and safety of pulsed versus continuous wave UVC.

Abstract

Purpose: Preclinical studies have confirmed efficacy of ultraviolet C (UVC) light in managing superficial corneal infections. This study sought to establish if delivering UVC in pulsed form enhances antimicrobial efficacy compared to continuous delivery, and whether pulsed delivery in ocular tissue results in deeper penetration or introduces additional safety concerns.

Methods: This study compared antimicrobial efficacy, depth of penetration, and safety of continuous versus pulsed wave delivery of UVC (20 Hz, 50% duty cycle) in three experimental setups. Firstly, efficacy was assessed using a simulated in vitro corneal wound model infected with bioluminescent P. aeruginosa, comparing matched-fluence, 0 to 120 s continuous wave versus 0 to 240 s pulsed wave exposures. Secondly, penetrability was evaluated in an ex vivo porcine corneal model (0 to 650 µm thickness). Lastly, safety was analyzed by immunohistochemistry to assess DNA photoproducts, cyclobutene pyrimidine dimers (CPD), focusing on their spatial distribution and density after UVC exposure (579 mJ/cm²).

Results: Comparable antimicrobial efficacy was observed for continuous and pulsed wave UVC (50% duty cycle) for all exposure durations (p > 0.05), except the 40 s pulsed wave, which was more effective than the 20 s continuous wave (p < 0.05). Corneal UVC transmission was limited and comparable for both delivery modes (all p > 0.05). Immunohistochemistry confirmed CPD were confined to the superficial corneal epithelial layers, with no significant differences in depth or extent of CPD formation between pulsed and continuous wave delivery modes (p > 0.05).

Conclusions: In in vitro and ex vivo testing, pulsed wave UVC demonstrated antimicrobial efficacy that was at least as good as continuous wave delivery, demonstrated comparable corneal depth penetration, and similar spatial distribution of CPD.