The COVID-19 global pandemic has had a profound effect on clinical care around the 66 world. As a result of the outbreak, many ophthalmology clinics temporarily halted elective 67 clinical visits and surgical procedures. Furthermore, the pandemic has resulted in fervent 68 discussion regarding best practices to limit the spread of infectious diseases in the clinical 69 setting. This disease, like many other upper respiratory infections, is highly transmissible via 70 respiratory droplets, with recent reports suggesting airborne transmission of the can also occur [1] [2] [3] . 71
Several independent ophthalmology organizations, including the American Academy of 72 Ophthalmology (AAO), have released guidelines regarding the resumption of clinical care as 73 well as recommendations on appropriate personal protective equipment (PPE) that should be 74 used when performing providing patient care. AAO guidelines recommend surgical masks for 75 patients, masks and eye protection for providers, and slit lamp breath shields 4 . However, there 76 has been limited evidence regarding the efficacy of these interventions. As clinical activities 77 resume, there is a need for robust data to inform use and efficacy of PPE in the clinic. Recent 78 work compared several commercially available slit lamp shields for degree of respiratory droplet 79 spread protection, providing necessary evidence for best clinical practice 1 . However, several 80 open questions remain for the development of best-practice, evidence-based guidelines for PPE 81 during the ophthalmic exam. In this study, we develop a patient cough simulator to evaluate 82 high-risk areas of respiratory droplet contamination during a slit lamp examination ( Figure 1 ). 83
Coughing simulator 85 All rights reserved. No reuse allowed without permission.
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The copyright holder for this preprint this version posted June 26, 2020. . https://doi.org/10.1101/2020.06.25.20140335 doi: medRxiv preprint simulation studies, was used as a simulator for patient coughing 5 . GloGerm MIST was sprayed 87 using the included pressurized spray canister, and the resulting mist was visualized using a images, photos were auto-aligned, the difference was calculated between images, then the 104 resulting difference was inverted and thresholded. 105
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The copyright holder for this preprint this version posted June 26, 2020. The slit lamp was next imaged before and after a simulated cough without a mask but 116 with a slit lamp shield. When the difference between the images were calculated, we observed a 117 majority of the respiratory droplets contained by the shield. However, we identified significant 118 contamination on the joystick as well as the slit lamp table (Figure 2d) . 119
We next assessed how well the surgical mask and slit lamp shield prevented respiratory 120 droplets from reaching the examiner. We sprayed GloGerm through the simulated patient with or 121 without a mask, and with or without a slit lamp shield present. When we compared images of the 122 board before and after the simulated cough, we were able to identify the pattern of droplets 123 reaching the examiner (Figure 2e ). When no protection was in place, a dense core of droplets can 124 be seen. A shield alone was able to block most of the central droplets, however peripheral 125 particles can still be seen (Figure 2f ). Minimal droplets were identified when the face mask was 126 present. Together, these data suggest a combination of a surgical mask and a slit lamp shield can 127 block a vast majority of forward-moving respiratory droplets. 128 All rights reserved. No reuse allowed without permission.
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The copyright holder for this preprint this version posted June 26, 2020. . https://doi.org/10.1101/2020.06.25.20140335 doi: medRxiv preprint Finally, we determined the microscopic architecture of the individual droplets (Figure 2f ) 129 seen in the previous experiment. Using SEM, we identified 3-10μm droplet nuclei contained 130 within one ~150μm respiratory droplet (Figure 2g) . 131
In this study, we characterized the risk to ophthalmologists from patients coughing 133 through a simulated patient slit lamp examination. Using simulated respiratory droplets, we 134 found the most effective intervention for containing spread was masking for both patient and 135 physician. When combined with a slit lamp shield, a majority of respiratory droplets are blocked 136 from reaching the examiner. We also identify the slit lamp joystick and examination table as a 137 high-risk area for contamination given its location under the shield, suggesting that gloves may 138 prevent physician contact with droplets. Our simulator is likely an underestimation of particle 139 spread, as GloGerm primarily forms droplets of 100μm, which is much larger than most 140 respiratory (>5-10μm) or airborne particles (<5μm) 6 . 141
Respiratory particles were observed escaping through the top of the mask lateral to the 142 nose, consistent with previous findings 7 , posing a risk when providers are close to the patient's 143 face such as during intravitreal injections or when using a direct ophthalmoscope. While further 144 studies are needed to fully evaluate the risk of virus transmission during close encounters, our 145 data suggest that use of eye protection is prudent. 146
Recent work suggests that surgical masks may be sufficient for reducing emission of viral 147 particles greater than 5μm, but less effective below that range 8 . Our SEM evaluation of 148 respiratory droplets reaching the provider identified droplets ranging from 3-100μm, suggesting 149 patient facemask alone is not sufficient to prevent all risk of respiratory or airborne 150 contamination. 151 All rights reserved. No reuse allowed without permission.
(which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. There are many limitations to this study. First GloGerm MIST may not be an exact 152 representation of respiratory secretions during a cough. While we are able to capture larger 153 particles, many of the droplet nuclei under 1μm are not detected by our fluorescent methodology. 154
In addition, we only tested one size slit lamp shield and one type of mask as a proof-of-concept. 155
Further work characterizing the efficacy of different commercially available masks and shields is 156 necessary for a complete understanding of the risks associated with clinic visits. 157
As ophthalmologic clinic appointments start to resume, additional data are needed to 158 provide best evidence-based guidelines for appropriate PPE in the clinic. Our cough simulation 159 experiments lend support for universal masking, slit lamp shields, as well as gloves to limit 160 exposure to potential SARS-CoV-2 during the ophthalmic exam. 161 All rights reserved. No reuse allowed without permission.
(which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.
The copyright holder for this preprint this version posted June 26, 2020. . https://doi.org/10.1101/2020.06.25.20140335 doi: medRxiv preprint