Benefits of Slip Lamp Breath Shields Confirmed

A new study has confirmed the benefits of slit lamp breath shields during the COVID-19 pandemic, with larger shields conferring the greatest protection.

Mong-Loon Kuet, MBBChir, FRCOphth, of Royal Derby Hospital, University Hospitals of Derby and Burton NHS Foundation Trust, and colleagues detailed the results of their study in a poster presented at the American Academy of Ophthalmology 2020 Virtual meeting.

“Slit lamp breath shields are widely recommended during the COVID-19 pandemic, yet little evidence exists on their effectiveness or ideal size,” Dr. Kuet and colleagues explained. “The ongoing pandemic has created an urgent need to address the effectiveness of different sized breath shields to improve user safety.”

Dr. Kuet and colleagues examined the effectiveness of a small and large slit lamp breath shield for transmission of fluorescein droplets after a simulated cough. The cough was simulated by a single spray from a conventional spray bottle containing 2 mL of fluorescein sodium 2% diluted in 10 mL of 0.9% saline.

The cough was performed with no shield, a standard 11 x 11 cm (4.3 x 4.3 inch) acrylic shield, and a larger 45 x 44 cm (17 x 17 inch) acrylic shield. Droplets were captured on a black detection screen placed 30 cm (about 12 inches) in front of the droplet source, where the slit lamp user’s face would be. The detection screen was then photographed under blue light.

In the control situation, droplets were distributed over the entire detection screen. With the smaller screen, droplets were detected at a radius of 4 cm to 15 cm (about 1.5 to 6 inches), including within the shield outline. However, with the larger size shield, no droplets were detected.

“Our findings suggest that larger breath shields confer greater protection against droplets from a simulated cough,” Dr. Kuet and colleagues wrote. “Standard sized smaller shields do not fully protect against these droplets, which may therefore reach the clinician’s face.”

They noted that there are tradeoffs with a larger shield, including contamination through inadvertent contact with the shield edges. They also emphasized that these shields should only be one part of an overall approach to infection control.

Finally, the researchers acknowledged that the cough simulator used in the study is not validated and does not fully model the physiological process of coughing. Despite that, the study offers “useful preliminary data on the protection provided by larger breath shields and supports their continued use by all clinicians during the COVID-19 pandemic and beyond.”