Hydrodynamic Interaction Between Tear Film and Air Puff From Noncontact Tonometry

Abstract

Purpose The purpose of this study was to investigate the mechanism of potential droplet formation in response to air puff deformation with two noncontact tonometers (NCTs). Methods Twenty healthy volunteers were examined using two NCTs, Ocular Response Analyzer and Corvis ST, and two contact tonometers, iCare and Tono-Pen. High-speed videos of the tear film response were captured with at spatial resolution of 20 microns/pixel at 2400 fps. Droplet size, droplet velocity, distance between air puff impact location, and the tear meniscus-lid margin were characterized. Results One subject was excluded due to technical issues. Droplets were detected only in tests with instilled eye drop. Videos showed the tear film rolls away from the apex while remaining adherent to the ocular surface due to the tendency of the fluid to remain attached to a solid surface explained by the Coanda effect. Twelve out of 38 videos with an eye drop administration showed droplet formation. Only one resulted in droplets with predominantly forward motion, which had the shortest distance between air puff impact location and lower meniscus. This distance on average was 5.9 ± 1.1 mm. The average droplet size was 500 ± 200 µm. Conclusions Results indicate no droplet formation under typical clinical setting. Hence, standard clinical use of NCT tests is not expected to cause droplets. NCT testing with eye drop administration showed droplet formation at the inferior eyelid boundary, which acts as a barrier and interrupts tear flow. Translational Relevance Study of tear film interaction with NCT air puff shows that these tonometers are not expected to cause droplet formation in standard use and that if external drops are required, both eyelids should be held if patients need assistance to maintain open eyes to avoid droplets with predominantly forward motion.

Validity of aerosolization detection with an air quality indicator in noncontact tonometry using corneal phantoms

“…The current study demonstrates significant differences using corneal phantoms without aerosol-generating potential, highlighting that a quasi-static (meaning that its sampling interval is very long relative to the event being monitored: 3 s relative to ~30 ms) AQI is not appropriate to measure a high-speed dynamic process. More appropriate technology would include advanced high-speed cameras much faster than the air puff duration, paired with imaging software ( 9 ) or shadowgraphy ( 10 ) which show consistent findings of no droplets being generated in natural settings unless external drops are added that would increase the tear load ( 9 , 10 ).…”