Abstract
Purpose :
To assess tear dynamics in response to air puff deformation with two noncontact tonometers (NCTs).
Methods :
The interaction between air puffs from two NCTs and the tear film were characterized using Phantom VEO 340s high-speed camera at a spatial resolution of 20 microns and a frame rate of 1500 fps. Exams were performed on right eyes of 20 healthy human volunteers with no history of dry eye or tear film instability. Each subject was examined before and after administration of one lubricant eye drop to the lower lid. 10 subjects received Ocular Response Analyzer (ORA) first followed by CorVis ST, while the rest received CorVis ST first followed by ORA. High-speed videos were further analyzed using Phantom Camera Control (PCC) software to quantify droplet size, instantaneous droplet velocity, and eyelid motion.
Results :
No droplets were detected for first NCT device used (both ORA and CorVis ST). Among the 40 exams with an eye drop administered, two exams resulted in droplets with a predominant forward motion (one from each device), while 11 exams showed droplet formation where the drop had a downward trajectory and did not remain suspended in the air. All droplets were emitted from lashes whether predominantly forward or downward motion. No droplets originated from the corneal surface. The average droplet diameter among all exams with eye drop administration was 502.9 ± 195.2 µm (range 210-970 µm). For the two exams with predominantly forward motion, two in-focus, forward-moving droplets were detected with each exam. Droplet velocities were 0.93 and 0.50 m/s for ORA and 1.72 and 1.32 m/s for CorVis ST exams.
Conclusions :
As the air puff arrives at the corneal surface, the tear film is pushed radially away from the apex while remaining attached to the corneal surface (Figure 1). This behavior, explained by the Coanda effect1, occurs due to the tendency of the tear film to follow the cornea curvature during deformation and results in droplets leaving the eye only at the eyelid boundary which interrupts tear flow. Droplet formation during NCT exams with different air puff strategies occurs only with eye drop administration, consistent with literature reports.
1D. J. Tritton, Physical Fluid Dynamics, 2012
This is a 2021 ARVO Annual Meeting abstract.