Study On The Mechanism Of Droplet Transmission And Exposure Risk Of Ophthalmologists In Ophthalmology Department

Since December 2019,COVID-19 has spread rapidly around the world,posing a serious threat to human health and causing incalculable impact on the global economy.Many countries have reported high infection rates among health care workers(HCWs),who may be cross-infected with patients in the course of their work,then accelerating the spread of the epidemic.Respiratory departments,ICU and surgery departments in hospitals have received wide attention due to their high infection risk,but ophthalmology has also found more infected cases among HCWs whose infection risk should not be neglected.To clarify the exposure risks of various routes faced by HCWs in the process of ophthalmic diagnosis,so that HCWs can fully realize the exposure risks they face,and provide precise and appropriate personal protection for ophthalmologists,so as to provide effective suggestions for the prevention and control of ophthalmic epidemic in the postoutbreak stage.In this paper,a thermal manikin with respiratory tract,a respiratory simulator and an aerosol release system designed and developed by ourselves were used to carry out a verification test in the clean room of the State Key Laboratory of Green Building in West China.Using three-dimensional modeling technology,a computational thermal manikins with oropharyngeal model and Weibel 0-4 level respiratory tract model was established,and built the numerical model according the clean room.New Poly-hexcore grid algorithm and real human breathing boundary conditions were employed.Simulated the exhaled droplets exposure of susceptible people based on the transient flow method and obtained particle concentration in exhaust air as a benchmark and the exposure dose from the environment to the human respiratory tract.By comparing the numerical simulation results with the experimental data,the average error between the two is 5.6 %,which confirms the reliability of the discrete phase model and the k-ω SST turbulence model to simulate the droplets and the air flow field,the discrete scheme and the boundary conditions.Subsequently,according to the standard ophthalmic examination process,the threedimensional numerical models of each human body and examination instruments in the direct ophthalmic examination,slit-lamp microscope examination and ophthalmic surgery in the ophthalmic examination room were built,which accurately simulated the postures and relative positions of the ophthalmologists and patients in each diagnosis process.The inhalation exposure,mucosal exposure and indirect exposure of HCWs during typical ophthalmic treatment were studied by numerical simulation method validated by the experiment.The results showed that ophthalmologists had different exposure risks in the three typical diagnosis processes.Under the same conditions,the direct exposure(inhalation exposure and mucosal exposure)of the ophthalmologist during direct ophthalmoscope examination was the largest,while the direct exposure during slit-lamp microscope was basically the same as that during ophthalmic surgery.However,the amount of droplet nuclei deposited on the surface of the instrument during slit-lamp examination was larger,resulting in a greater risk of indirect exposure.Compared with the data in the existing literature,it is found that the risk of inhalation exposure of ophthalmologists is greater than that of other interpersonal interaction scenarios.In particular,the inhalation exposure of ophthalmologists during direct ophthalmoscope examination is about 95 times as much as that when the interpersonal distance is 1.0 m.According to the calculation results of various exposure routes in the course of ophthalmic diagnosis,it is suggested that appropriate and precise personal protection must be taken for ophthalmologists.N95 masks,goggles or protective masks must be worn to significantly reduce the direct exposure risk to ophthalmologists.Disinfection measures must be carried out in time after the use of the inspection equipment.Finally,the factors affecting ophthalmic exposure risk were studied.It was found that during the slit lamp microscopic examination,the inhalation exposure amount of patients during cough was about 7.6 times of that during breathing,and the mucous membrane exposure was 16.8 times of that during breathing.Most of the cough droplets settled on the slit lamp,the table top and the human body.This is due to the cough exhaled air velocity,high droplets momentum and the influence of gravity.In direct ophthalmoscope examination,inhalation exposure was the highest when the respiratory phase difference was π,mucosal exposure and contact exposure was the highest when the phase difference was π/2,and the instrument surface settlement was the highest at 3/2π.In addition,the relative humidity of droplet evaporation process,has remarkable effect on movement and diffusion in the slit lamp microscope examination in patients with cough of 50 microns droplets evaporation rate with the increase of relative humidity decreased significantly,and eye doctor inhalation exposure and mucous membrane exposure also decreases with the increase of relative humidity,but indirect exposure increases,Therefore,a moderate increase in ambient humidity is beneficial to reduce the exposure risk of ophthalmologists.In addition,with the increase of particle size,the number of droplets suspended in the respiratory zone of doctors decreased,and thus the inhalation exposure,mucosal exposure and contact exposure of ophthalmologists also decreased.However,the number of droplets settling on the slit lamp microscope increased significantly,leading to an increased risk of indirect exposure.