Contamination of the slit-lamp breath shield under face-masking conditions: a prospective clinical study

Abstract Objective Ophthalmologists have installed breath shields on slit-lamp microscopes to block droplets produced by patients and prevent infection with severe respiratory syndrome coronavirus 2, the cause of the coronavirus disease 2019 pandemic. This study measured the contamination of one such shield used in clinical practice under face-masking conditions and examined its significance in preventing infection.Methods In this single-center prospective study, measurements were taken at an ophthalmology outpatient unit on 10 weekdays: 5 consultation days and 5 closed days. All patients were required to use face masks, including surgical masks, commercially available cloth masks, and homemade cloth masks. A breath shield, made of polyethylene terephthalate, was hung on the eyepieces of the slit-lamp microscope. Measurement areas of 25 cm2 were set on the patient-side surface of the shield, as well as on the slit-lamp table, where touching was not forbidden. Samples were collected after wiping with 78 vol% ethanol at 9 a.m., at the beginning of office hours. Touching the shield was forbidden during office hours, and the samples were collected again at 5 p.m., at the end of office hours. The total amount of adenosine triphosphate + adenosine diphosphate + adenosine monophosphate was measured as an indicator of the degree of contamination.Results Contamination of the shield had increased by the end of office hours on the consultation days, although the p-value from a paired t-test was slightly above 0.05. In contrast, on days when the department was closed, no difference was observed in the level of contamination between morning and evening. Similarly, the slit-lamp table was significantly contaminated on consultation days, whereas there was no difference in contamination between morning and evening on closed days.Conclusions This study suggests that droplets from patients can still reach the shield even when the patients are wearing a mask.