Far-Ultraviolet C Disinfection Reduces Oxidative Damage to the Cornea Compared to Povidone-Iodine Disinfection

Abstract

Far-ultraviolet C (far-UVC) light shows promise for pathogen control but its safety and efficacy for corneal disinfection remain unclear. In this study, safe far-UVC dosages were investigated for corneal disinfection and its germicidal performance and oxidative damage potential to 5% povidone-iodine (PVP-I) were compared. Rat corneas were exposed to varying 222 nm far-UVC doses (3-60 mJ/cm²) and assessed for ocular damage, apoptosis, and oxidative stress to determine the safe dose of far-UVC. Far-UVC at 30 mJ/cm² induced corneal apoptosis and oxidative damage, but 15 mJ/cm² caused no apoptosis or oxidative damage. At this optimized dose (9 mJ/cm²), far-UVC achieved 90.5% sterilization, exceeding 5% PVP-I (80.8%), with significantly less oxidative damage and cell death in the cornea. In conclusion, our study demonstrates that the use of 5% povidone-iodine (PVP-I) for disinfection results in significant oxidative damage to the corneal tissue. However, a safe dosage of far-UVC light exhibited a promising disinfection effect without causing oxidative damage to the corneal tissue. Far-UVC offers a promising alternative for corneal disinfection but requires careful dosage control (≤30 mJ/cm²) to avoid ocular surface harm.

Keywords: 222 nm far-UVC; apoptosis safety; cornea; disinfection; oxidative damage; povidone-iodine.

Figure 1

Analysis of the corneal epithelium damage through the H&E stain after far-UVC exposure. (A) Representative images of the corneal section in the different far-UVC dose-treated groups. Arrows point to ruptured areas or lysed cells of the corneal epithelium. (B) Quantification of ruptured areas or lysed cells in the corneal epithelium for each group. (* p < 0.05, **** p < 0.0001). Data are expressed as the mean ± SD.; H&E, hematoxylin, and eosin staining. ns, not significant. Scale bar: 40 μm.

Figure 2

The corneal injuries after the designated doses of far-UVC exposure. (A) Representative images of fluorescent staining of oxidative stress in the corneal stroma. (B) Quantification of the dihydroethidium (DHE)-positive cells per high-power field (HPF). The number of DHE-positive cells in the 30, 45, and 60 mJ/cm² of far-UVC-treated groups were significantly higher than the non-treated group (** p < 0.01, **** p < 0.0001). (C) Representative images of apoptotic cells in the corneal epithelium. (D) Quantification of the number of the TUNEL-positive cells per HPF. The number of apoptotic cells in the 30 and 45 mJ/cm² of far-UVC-treated groups was significantly higher than in the non-treated group (* p < 0.05, **** p < 0.0001). Data are expressed as the mean ± SD. DHE, dihydroethidium; HPF, high-power field; TUNEL, TdT-dUTP nick end-labeling. ns, not significant. Scale bar: 100 μm.

Figure 3

The total viable count on rat ocular surface after far-UVC exposure. (A) Representative images of total viable count for rat ocular surface after far-UVC exposure. (B) Quantification of total colonies for each group. The CFU in the far-UVC-treated groups was significantly lower than in the non-treated group (** p < 0.01, *** p < 0.001, n = 4 per group). Data are expressed as the mean ± SD.

Figure 4

Comparison of disinfection efficacy between 5% PVP-I and 9 mJ/cm² of far-UVC in rat ocular surface. (A) Representative images of the total colonies on the TSA plate for each group. (B) Quantification of total colonies on the TSA plate. The number of the total colonies in the 5% PVP-I-treated and 9 mJ/cm² of far-UVC-treated groups was significantly lower than in the non-treated group (** p < 0.01). (C) Quantification of the colony number of 4 bacterial species. The lowest colony number was found in the 9 mJ/cm² of the far-UVC-treated group for all bacterial species (* p < 0.05, ** p < 0.01, *** p < 0.001). Data are expressed as the mean ± SD.

Figure 5

Comparison of corneal injuries in the rat cornea between 5% PVP-I treatment and 9 mJ/cm² of far-UVC exposure (A) Representative images of the oxidative stress in the corneal stroma for each group. (B) Quantification of the DHE-positive cells per HPF. The number of DHE-positive cells in the 5% PVP-I-treated group was significantly higher than those in the non-treated group and the 9 mJ/cm² of the far-UVC-treated group (** p < 0.01, n = 6 per group). (C) Representative images of apoptotic cells in the corneal epithelium in the non-treated, the 5% PVP-I-treated, and the 9 mJ/cm² of the far-UVC-treated group. Red arrowheads indicate the TUNEL-positive cells, and white arrowheads indicate the cavities in the corneal epithelium. (D) Quantification of the number of TUNEL-positive cells per HPF. A significant increase in the number of TUNEL-positive cells was found in the 5% PVP-I-treated group than the other groups (**** p < 0.0001). Data are expressed as the mean ± SD. HPF, high-power field; dihydroethidium (DHE)-labeling. TUNEL, TdT-dUTP nick end-labeling. Scale bar: 100 μm.