Quantitative Evaluation of Aerosol Generation from Non-contact Tonometry and its Correlation with Tear Film Characteristics

Abstract

Introduction Ophthalmologists are inevitably exposed to tears and ocular discharge during ophthalmologic examinations and are at high risk for SARS-CoV-2 infection. To understand the role of aerosols in disease transmission, we adopted a prospective cross-sectional study design and investigated the count and size distribution of aerosols generated by a non-contact tonometer and its correlation with individual tear film characteristics. Methods This study constituted two parts. The study population included outpatients who underwent an intraocular pressure examination in an intraocular pressure examination room (Part I) and 20 participants who underwent an intraocular pressure examination in a laboratory (Part II). The following main outcomes were measured: aerosol counts at 0, 50, 100, 150, and 200 cm from the non-contact tonometer (Part I); aerosol counts after each participant underwent non-contact tonometry, and lipid layer thickness score and tear film break-up time (Part II). Results The aerosol count decreased with increasing distance from the tonometer. The aerosol count at 0 cm had the highest value compared to that at other distances. For aerosols of diameters 0.25–0.5 μm and 0.5–1.0 μm, the count decreased at 50 cm and remained stable at further distances. For aerosols of diameters 1.0–2.5 μm and ≥ 2.5 μm, the count dropped progressively at all five distances. The aerosol count from each tonometer correlated positively with the lipid layer thickness score ( r = 0.490, P = 0.028), whereas the aerosol count correlated negatively with the tear film break-up time ( r = − 0.675, P = 0.001). Conclusions Aerosols tended to coagulate during diffusion. A 50-cm distance from the tonometer could confer safety from aerosols with < 1.0-μm diameter. Aerosols generated during non-contact tonometry could contain a lipid layer component. Moreover, tear film stability could affect aerosol generation. Protective eyewear is recommended for reducing infection risk from aerosols. Individual tear film characteristics should be considered during non-contact tonometry.

The Role and Views of Ophthalmologists During the COVID-19 Pandemic

“…17 In addition, in low-income countries, patients were provided with disinfectants. 18,19 Recommendations for the ophthalmological sector included intensive cleaning of instruments (slit lamps and lenses) after each patient 20 and avoidance of on-contact tonometry 21 because of the possibility of aerosolisation of virus particles. In order to classify the results correctly, the timing of the studies and the large regional differences in infection numbers must be taken into account, in addition to the low response rates, which mean that the results can not be considered representative for most countries.…”

Assessment of temporal and spatial distribution patterns of aerosol produced by air-puff non-contact tonometer

“…Specifically for aerosol derived from NCT, the particles with a diameter ranging from 0.25 μm to 0.5 μm accounted for >96% of the whole. 12 As the PM 2.5 concentration was still higher than baseline in the 30 s, it was rational to assume that particles with smaller diameter may keep floating in the air even longer without ventilation. Considering our clinical settings, we suggest that the caregivers avoid continual NCT measurement without interval between patients.…”

“…11 Meanwhile, similar to tear droplets, the production of aerosol with smaller particle diameter was also increased. [12][13][14] Binding to aerosol, the virus particle may gain prolonged existence and increasing distance of spread. 15 As the aerosol dispersion has been considered a potential route of COVID-19 transmission, 15 both the patients and operators may suffer the risk of exposure during the IOP measurement.…”

“…16 Previous studies had revealed a cumulative effect of aerosol based on the number of air-puff 14 and its attenuation with distance. 12 However, the duration and direction of aerosol spreading were not fully evaluated, which should be more practical to clinical protection. Hereby, the current study aimed to assess the distribution pattern of PM in the aspect of time and direction during the IOP measurement by NCT.…”

The Implications on Future Ophthalmic Care During and Post-COVID-19

“…One of the latest study from our team demonstrated that a 50 cm distance from the tonometer might confer safety from aerosols with <1.0-µm diameter. Patients with aqueousdeficient dry eyes would tend to generate more aerosols, and the use of protective eyewear in clinical settings for both doctors and patients were recommended (27). Good clinical protection can provide a feeling of safety for both ophthalmic care providers and patients.…”