• Written By:
    Comprehensive Ophthalmology

    Review of: Visualizing Speech-Generated Oral Fluid Droplets with Laser Light Scattering

    Anfinrud P, Bax C, Bax A. New England Journal of Medicine, April 15, 2020

    In this study, investigators used light scattering to visualize trajectories of speech-generated droplets with and without a mask.

    Study design

    The authors used a 532-nm green laser transformed into a light sheet that was approximately 1 mm thick and 150 mm tall. They directed this light sheet through slits on the sides of a cardboard box. The box, which was painted black interiorly, was positioned under a high-efficiency particulate air (HEPA) filter to eliminate dust. A volunteer was asked to speak through the open end of the box.


    When the volunteer said, “stay healthy,” numerous droplets ranging from 20 to 500 μm were generated. These droplets produced flashes as they passed through the light sheet; the number of flashes per video frame was highest when the “th” sound in the word “healthy” was pronounced.

    When the same phrase was uttered through a slightly damp washcloth over the speaker’s mouth, the flash count remained close to the background level. The study included a video of the experiment showing the speech-generated droplets.


    The authors did not assess the relative roles of droplets generated during speech, droplet nuclei and aerosols in the transmission of viruses.

    Clinical significance

    This experiment adds to the body of evidence that masks do reduce the transmission of droplets and should encourage patients and doctors to wear a mask when speaking. This serves as a reminder to health care providers of the dangers that can exist by not wearing a mask during sterile surgical procedures.