For decades, germicidal UVC radiation (peak emission 254 nm) has been used to disinfect the air, water and non-porous surfaces from bacteria, germs and viruses. But these wavelengths pose a threat to the skin and the cornea, and therefore are only used in unoccupied spaces.
Research ensued to find a safer band of wavelengths for UV disinfection. In a 2016 study, a narrow UVC wavelength band of 200 to 222 nm irradiated and efficiently killed bacteria. Even drug resistant bacteria was killed and without damaging cells in living tissues. Scientist refer to this as far-UVC.
Researchers at Columbia University Irving Medical Center investigated far-UVC (222 nm) and discovered that it was safe for human exposure as it did not penetrate the eyes’ tear film or the outer dead skin cell layer. They also discovered that 222 nm could kill airborne influenza viruses. By testing two common corona viruses that were aerosolized, they found that 99.9 percent of the exposed virus was killed by very low exposure to far-UVC radiation. With continuous exposure to far-UVC at the current regulatory level limit 90 percent of viruses are killed within 5 minutes, and 99.9 percent within 25 minutes of exposure. Both the wavelength and the correct dose of far-UVC is needed to deactivate the virus, the study indications are that 222 nm far-UV light doses of only 1.7 mJ/cm2 or 1.2 mJ/cm2 respectively produce 99.9 percent inactivation of the virus. But we want to know if it kills the COVID-19 (SARS-CoV-2) virus. In a separate and ongoing study, preliminary data suggests that far-UVC is equally effective at killing the COVID-19 virus, even airborne droplets and aerosols.
A word of caution to the ECP—many UV products claim to disinfect eyeglasses but without the proper dose, time and wavelength, bacteria and viruses could remain on the frames for the next patient to try on. The worse scenario is that you and the patient have a false sense of safety because you assume the effectiveness of the instrument. The FDA suggest that one consider both the risks of UVC lamps to people and objects, and the risk of incomplete inactivation of virus. They suggest that you ask the manufacturer about health and safety risks and instructions for use/training information. Ask whether the product generates ozone. Ask what kind of material is compatible with UVC disinfection. Ask whether the lamp contains mercury for safe handling or disposal.
In the upcoming November 20/20 issue, you can learn about a new safe, efficient and fast eyeglass frame disinfectant tool ZEISS UVClean and earn a free ABO credit.
• Deborah Kotob
Pro to Pro Director