Chronic Far-UVC (222nm) Light Exposure of SKH-1 Hairless Mice Does Not Cause Detectable Eye Pathology or Visual...

Far-UVC light (200-235 nm) is a new antimicrobial technology proposed for use in occupied spaces. In contrast to conventional germicidal UV light (254 nm), theoretical considerations and emerging safety data suggest that the decreased penetration depth of shorter wavelength far-UVC light causes less damage to vulnerable eye and skin tissue. This study examined the ocular effects of chronic far-UVC exposure in hairless, immune-competent SKH-1 mice after long-term exposure.

Over 66 weeks, five days/week, eight hours/day, 48 each male and female mice were exposed to high (400 mJ/cm²), medium (130 mJ/cm²), low (55 mJ/cm²), or no (0 mJ/cm²) far-UVC (222 nm) light. Visual acuity and contrast sensitivity was determined using optokinetic methods, slit lamp examinations were made of the anterior segment, and intraocular pressure was determined. Analysis of corneal images quantified the extent of corneal neovascularization.

No significant differences in visual acuity, contrast sensitivity, intraocular pressure, or corneal neovascularization were observed between unirradiated animals and exposure groups. All groups, including unexposed controls, exhibited some degree of corneal neovascularization. Male mice had significantly lower visual acuity and contrast sensitivity than females. Stratified by gender, there was no exposure condition-based difference in contrast sensitivity. These findings were consistent whether each animal's eyes were averaged. or if all eyes were assessed individually.

There was no relationship between far-UVC dose and visual acuity, contrast sensitivity, ocular pressure, or corneal neovascularization. Female mice had significantly higher visual acuity and contrast sensitivity. No ocular pathologies were observed, even at 400 mJ/cm², substantially above the recently enacted ACGIH safety threshold of 160 mJ/cm² for 222 nm ocular exposures. More sensitive or detailed corneal examinations, longer daily exposures, or higher far-UVC doses, may be useful to define thresholds for human eye safety.