Dewetting Characteristics of Contact Lenses Coated with Wetting Agents

TL;DR

This study systematically analyzes how different wetting agents influence tear film stability on contact lenses, revealing key physio-chemical factors that improve wetting performance and delay dewetting.

Contribution

It provides a comprehensive in vitro evaluation of multiple wetting agents, establishing correlations between their properties and tear film dewetting mechanisms.

Findings

Zwitterionic agents stabilize tear film by reducing dewetting onset thickness.

Tuning surface concentrations enhances wetting characteristics.

Dewetting time scales linearly with contact angle metrics.

Abstract

Hypothesis: Although wetting agents have been developed to limit tear film dewetting over contact lenses, systematic analyses correlating wetting agents properties to mechanisms of the tear film destabilization are not readily available. Clarifying destabilization characteristics across key physio-chemical variables will provide a rational basis for identifying optimal wetting agents. Experiments: We employ an in-house, in vitro platform to comprehensively evaluate drainage and dewetting dynamics of five wetting agents across seventeen different formulations and two model tear film solutions: phosphate-buffered saline (PBS) and artificial tear solution (ATS). We consider the film thickness evolution, film thickness at breakup, dewetted front propagation, and develop correlations to contact angle to compare the samples. Findings: Zwitterionic wetting agents effectively stabilize the tear film by reducing the film thickness at the onset of dewetting, and delaying dewetted region propagation across the lens. Furthermore, tuning wetting agent surface concentrations in binary mixtures can enhance wetting characteristics. Finally, despite disparities in wetting agent molecular properties, the time to dewet $50\%$ of the lens scales linearly with the product of the receding contact angle and contact angle hysteresis. Hence, we fundamentally establish the importance of minimizing both the absolute contact angle values and contact angle hysteresis for effective wetting performance.