Abstract
Purpose :
Effective biotribological lubrication of dry ocular surface was reported as correlating with ocular comfort score and needs a minimum lubricant film thickness to be sustained significantly above thickness of natural tear film. This study aimed to analyze the dynamic interactions between lubricant droplet and ocular surface and to introduce the rate of droplet thinning, while droplet is spreading, as a benchmark for predicting lubricant biotribological merits.
Methods :
Droplet touchdown on ocular surface triggered the recording of droplet motion. Ten frames per second were captured from AVI movie, framing a 40 microliter lubricant droplet above a face-up placed ocular surface of freshly excised rabbit eyeglobe at induced dry eye condition. Droplet boundaries, its contact angle and droplet cross-section width were auto-determined from captured frames by FTA-188 algorithm (First Ten Angstroms Inc.) allowing the extraction of droplet central-height (h) and base-area radius (r). Studied lubricants were cationic (CEM) and anionic (AEM) nanoemulsions (core oil, emulsifier, surfactant, and cationic or anionic entity) and polyanionic hyaluronate 0.1% (SH).
Results :
Spreading of CEM droplet was swift and its height (h[CEM]) fell sharply. Between 0.1 and 0.3 seconds after touchdown, h[CEM] went from 0.5+/-0.1 mm to 0.3+/-0.1 mm (p .0291) and then down to an approaching-zero plateau after 2 seconds. In contrast, the droplet height of AEM and SH went down moderately. In the 1-10 seconds interval, h[AEM] went down from 1.7+/-0.3 to 1.2+/-0.2 mm (p .0715), and h[SH] went down from 2+/-0.8 to 1.2+/-0.6 mm (p .2321). Regression analysis of h and r relationship returned h=0.4658e[-0.063r] (R2=0.9655) for CEM, h=5.9312e[-0.354r] (R2=0.9993) for AEM and h=3.9905e[-0.217r] (R2=0.9692) for SH.
Conclusions :
CEM droplet swift spreading reflects, in part, the electrostatic attraction of the cationic CEM to the anionic entities that dwell at ocular surface. Yet, the associated swift thinning of CEM droplet is not corresponding with favorable biotribological merits. In contrast, biotribological features can still be realized for the anionic AEM and SH, as both sustained a minimum film thickness significantly above thickness of natural tear film. The results showcase the merits of lubricant droplet motion imaging after topically applying a droplet on ocular surface and introduce the thinning rate of lubricant droplet as a biotribological benchmark.
This is a 2021 ARVO Annual Meeting abstract.