Methods
cough, dry’ cough
EYE
We used a cough model, taped to a slit lamp in the University of Portsmouth Eye Clinic. The cough model uses an Ambu bag connected to 40 cm of 30 mm endotracheal tubing. We calibrated this to give a FEV1 between 290 and 370 l/mm, similar to a human cough. To produce a ‘dry’ cough we used 0.5 ml of normal saline, stained this with 1 mg/100 ml fluorescein (Fig. This is the  experimental setup, the paper targets are pinned to a board and the breath-guard is in place.We used a randomised controlled trial method, random numbers were used to determine whether the breath-guard, breath-guard with a face-mask or control. The breath-guard we used was 300 mm high and 350 mm wide and was attached to the eye pieces of the slit lamp (Fig. An example of a splatter pattern and no breath-guard.We placed a target of four A4 printed sheets on a board at 40 cm (the standard position of the observer eyepieces) from the cough model, behind the slit lamp and triggered the ‘cough’. The targets were imaged under UV light in a dark room, using a blue blocking filter (Tiffen, New York, Orange 16). Sets of images were taken with the control (22), the breath-guard (11) with the breath-guard and face-mask (11).The images were first de-warped to correct the camera angle, and a source detection algorithm, Source Extractor [This figure shows the software detection of droplets on the target paper sheets, each droplet is circled in red, before the size, brightness is measured.This research was submitted to the University of Portsmouth Ethics screening tool ref: 10247.