Corneal safety assessment of germicidal far UV-C radiation

Far UV-C radiation (200-240 nm) is a promising alternative to conventional UV-C for disinfection in occupied spaces, offering strong germicidal efficacy with reduced skin risk. However, its ocular safety remains unclear, as most studies relied only on non-human corneal models with physiological differences. This study investigated UV-induced DNA damage in the epithelium, stroma, and endothelium of ex vivo human corneas and porcine corneas, and reconstructed human cornea epithelium (RHCE) using immunohistochemistry. Samples were exposed to 222 nm, 233 nm, 254 nm, and broadband UV-B (280-400 nm) radiation in the presence of real human tears. Compared to human corneas (26 μm mean epithelium thickness), porcine corneas (110 μm) and RHCE (79 μm), showed reduced UV penetration. In human corneas with a thin epithelium, far UV-C exposure led to epithelial and anterior stromal damage, underscoring the epithelium's protective function. Optical properties using porcine corneas confirmed the immunohistological findings, validating wavelength-dependent penetration depths. Simulations suggest that in intact human corneas, damage-relevant intensity of 222 nm light reaches the middle of the epithelium, while for 233 nm, it reaches the basal layer. These findings support the relative safety of far UV-C, especially 222 nm, for intact corneas. However, potential DNA damage accumulation after repeated exposures underscores the need for further research on long-term ocular effects.