key: cord-0705590-sd9hbocg
authors: Felfeli, Tina; Batawi, Hatim; Aldrees, Sultan; Hatch, Wendy; Mandelcorn, Efrem D.
title: Utility of patient face masks to limit droplet spread from simulated coughs at the slit lamp
date: 2020-07-27
journal: Can J Ophthalmol
DOI: 10.1016/j.jcjo.2020.06.010
sha: 60df11b61ba4efb0daf291624c286f4e384f5292
doc_id: 705590
cord_uid: sd9hbocg

nan

With the accelerated spread of the severe acute respiratory syndrome coronavirus 2 leading to coronavirus disease 2019 pandemic, there are unprecedented challenges on the medical community. Of major concern are the high titres of virus in the oropharynx early in the disease course, and long incubation period (5À7 days) of asymptomatic shedding of severe acute respiratory syndrome coronavirus 2. 1 Effective use of personal protective equipment (PPE) such as gloves, face masks, goggles, face shields, and gowns is critical to prevent the spread of infection to and from health care workers and patients. This is particularly important to clinicians who work in close proximity with the patient's face such as when performing slit-lamp examinations. Accordingly, the American Academy of Ophthalmology has recommended that patients not speak during slit-lamp examinations as well as the use of commercially available slit-lamp barriers or breath shields as an added measure of protection. However, breath shields may not fully eliminate the spread of droplets. 2 The use of masks by patients has been shown to mitigate the emission of various viruses into the environment and is recommended by the Centers for Disease Control and Prevention. 3 Herein, we aimed to investigate how various scenarios of masks worn by patients can reduce the spread of respiratory droplets onto the examiner during a slit-lamp examination using a simulated patient cough.

In a simulation, an ophthalmologist donned in standard PPE including a face mask and eye protection was positioned looking through the oculars of the slit lamp (BM 900 Haag-Streit). The slit lamp had a commercially available breath shield hung on oculars measuring at 9.75 inches in width and 10.5 inches in height (Carl Zeiss Meditec AG). A manikin (Vera cardiopulmonary resuscitation model, Canadian Red Cross) was placed at the chin rest of the slit lamp to simulate a patient under examination. To standardize the target distance, the slit lamp was focused on the manikin's right eye. A patient cough was simulated using a small latex balloon that was compressed with oxygen and 1.25 mL of washable fluorescent dye that was run through tubing inside the manikin and placed inside the oral cavity. The balloon was inflated until it burst at 5 pound-force per square inch, which has been previously reported as the force for a voluntary cough and laryngeal cough reflex. 4 The simulation was performed under ultraviolet light conditions (light-emitting diode 395NM ultraviolet flashlight, WJZXTEK) in order to visualize emission of fluorescent small particles, which included a mixture of dry and wet particles measuring at 30À100 mm for varied particle-size distribution (UV neon fluorescent blacklight paint kit, Paint Glow). 5 A video of the simulation that is slowed down by a factor of 8 at 240 frames per second is available online (Video 1, available online). These methods have been previously validated for visualization of cough droplets. 6, 7 The initial simulation was repeated for 10 rounds, and subsequent series of simulations were repeated twice each to confirm consistency of observed findings. A multistep process including use of different colour dyes, thorough cleaning of equipment and manikin, as well as switching the examiner's PPE was done to ensure that no cross-contamination between each simulation interfered with the findings.

In the next stage of this initiative, we aimed to identify means of further reducing the droplet spread by focusing on the use of masks for the patient under examination. Repeat simulations were conducted with (i) one of the most readily available cloth masks (black cotton face mouth mask); (ii) an ear loop surgical mask (American Society for Testing Materials Level 2, 3M) positioned incorrectly (loose and covering the mouth only to mimic a commonly encountered circumstance); (iii) an ear loop surgical mask with proper positioning (American Society for Testing Materials Level 2, 3M); and (iv) an N95 mask (Model 8210, 3M, not fitted to the manikin). The spread of droplets onto the field of the examiner and the slit lamp was identified under ultraviolet light conditions in each simulation as described above.

This simulation demonstrates that the use of slit-lamp breath shields and standard PPE for the examiner may reduce but does not eliminate the projection of droplets onto the examiner's field, chest, shoulders, and arms (Fig. 1) . The spread of smaller droplets was also identified on the bouffant cap, gloves, and shoes of the examiner. Further contamination of the floor, walls, and window covers were identified within the room. In the simulation with a cloth mask, droplets were identified on gloves of the examiner, and on the slit lamp. An inspection of the inside of the mask demonstrated the spread of droplets beyond the outer borders of the mask on the superior, inferior, and lateral edges (Fig. 2) . In the simulation involving the improperly positioned surgical mask, droplets were identified on the shoulders, arms, and gloves of the examiner as well as the slit lamp, floor, and walls. With the surgical mask properly positioned, the examiner was clear of droplets; however, some droplets were noted on the side bars close to the chin rest of the slit lamp. No droplets were identified on the examiner or the slit lamp in the repeat simulation with the use of the N95 mask. A view of the inside of the mask also revealed that droplets were contained within the mask.

This simulation aimed to visualize the spread of respiratory droplets onto the examiner at the slit lamp. Our findings suggest that the use of a properly fitted mask on the patient as an adjunct to the current standard PPE used by the examiner, and the breath shield is essential for limiting droplet dissemination during slit-lamp examinations. Cloth masks decrease the spread of respiratory droplets onto the examiner and can be even more effective than a surgical mask that is worn incorrectly. However, spread of some droplets was noted on the hands of the examiner during the slit-lamp examination with cloth masks. This may be owing to the poor design and poor flexibility of the material used to make cloth masks, which can lead to gaps through which respiratory droplets can disseminate easily. If worn correctly, surgical masks greatly reduce the spread of droplets onto the examiner. Although shown to be effective in this simulation, the current limited resources Q1 X X of N95 masks that have not been professionally fitted, for routine clinical encounters is not supported. These findings are consistent with other studies that have demonstrated reduced droplet transmission when wearing a face mask. 8 In addition to decreasing the spread of droplets, surgical masks worn by patients have been found to decrease the emission of different viruses into the environment, including influenza virus and coronavirus. 3 It is important to note that this simulation does not identify the spread of very small particles and droplets. Although the bursting pressure for the balloon was adjusted to simulate a voluntary cough, the volume of the cough was overproduced beyond what would be expected in a natural cough in order to account for the potential extent and multidirectional spread of a true cough in various scenarios under one simulated setting. No means of accounting for turbulence of mucosalivary filaments in a simulated cough have been previously reported and thus were not accounted for in this simulation. Given that the goal of this simulation was to provide effective means of protecting the examiner, we did not assess the spread of droplets beyond the slit lamp and the examiner with the use of various masks. Furthermore, some variations may be noted in repeat simulations. Lastly, appropriate PPE for the examiner should be selected on a case-by-case basis for patients who are low risk, suspect, or confirmed positive for coronavirus disease 2019 and based on the recommendation of the local health authority.

Overall, this simulation demonstrates the potential spread of droplets during a slit-lamp examination from a patient cough onto the examiner, equipment, and room. Based on this, our recommendations for the use of masks for patients include the following: (i) patients should wear a mask during slit-lamp examinations (including a well-fitted cloth mask if it is the only available option); (ii) correct positioning of the mask is critical, and an improperly fitted mask may provide a false reassurance of protection; (iii) slit lamps should be disinfected between patients to prevent cross-contamination.

Conflict of Interest: No conflicting relationship exists for any author. 

Supplementary material associated with this article can be found in the online version at doi:10.1016/j. jcjo.2020.06.010. X X each of the masks used in repeat simulations, spread of droplets, and droplets within the inside of the masks visualized with ultraviolet light. With the properly positioned cloth mask (A1), the examiner had spread of droplets onto gloves (A2). Droplets spread beyond the outer borders of the mask (A3). With the improperly positioned surgical mask (B1), the examiner had droplets on the gloves, arm, chest, and shoulders (B2). Droplets spread beyond the outer borders of the mask (B3). With a properly positioned surgical mask (C1), the examiner was clear of droplets, but droplets were detected on the side bar of the slit lamp (C2). No droplets spread beyond the outer borders of the mask (C3). With a properly positioned N95 mask (D1), no droplets were detected on examiner or the slit lamp (D2). No droplets spread beyond the outer borders of the mask (D3).

Early transmission dynamics in Wuhan, China, of novel coronavirusÀinfected pneumonia

Efficacy of slit lamp breath shields

Respiratory virus shedding in exhaled breath and efficacy of face masks

Intra-abdominal pressures during voluntary and reflex cough

Cough aerosol in healthy participants: fundamental knowledge to optimize droplet-spread infectious respiratory disease management

Coughing and aerosols

Barrier enclosure during endotracheal intubation

Visualizing speech-generated oral fluid droplets with laser light scattering

Footnotes and Disclosure Quality Improvement Grant, Department of Ophthalmology and Vision Sciences