In Vitro Monitoring of Drainage and Dewetting Dynamics over Contact Lenses Coated with Wetting Agents

Contact lenses are known to alter the stability of the tear film over the course of a blink cycle. Dewetting of the tear film results in a number of ophthalmic disorders including dry eyes, poor vision, and discomfort. To avoid these undesirable consequences, contact lenses are coated with wetting agents to prevent the untimely dewetting of the tear film. Despite the availability of a few commercial lenses with such coatings, there are not many studies that have systematically investigated the drainage and dewetting dynamics over contact Lenses coated with wetting agents. To address this knowledge gap, we report (a) an in vitro platform for high throughput characterization of tear film drainage and dewetting over contact lenses, and (b) a systematic analysis of the effect of various wetting agent chemistries and surface concentration on the drainage and dewetting dynamics.

The in vitro setup that we call as the Interfacial Dewetting and Drainage Optical Platform (i-DDrOP) consists of a dome (mimicking the eyeball) for holding the lens, a trough for holding a solution mimicking the tear liquid and a custom build interferometer consisting of a white LED light and a CCD camera. During an experiment, the contact lenses is placed on the dome and the arrangement is submerged in the liquid inside the trough. Subsequently, the dome along with the lens is elevated above the liquid surface, resulting in a thin liquid film to form over the lenses (analogous to the tear film that forms after a blink). The evolution of this liquid film is tracked by the interferometer. The obtained interference patterns are analyzed using Python and MATLAB to characterize the drainage and dewetting dynamics. Drainage analysis focuses on a single point (initial site of dewetting) on the lens surface and monitors the film thickness over time until the point of dewetting. The dewetting analysis, by contrast, focuses on the rate of propagation of a dewetted area across the entire lens surface. Lenses with no coatings, single component coatings (four different types), and binary mixtures of coatings at different surface concentrations were analyzed. Utilizing information from the drainage and dewetting analysis, we identify optimal surface coatings and related surface concentrations that can prevent the untimely dewetting of the tear film.