Quantifying the Effects of Recombinant Human Lubricin on Model Tear Film Stability

Dry eye disease (DED) is an ocular pathology affecting hundreds of millions of patients worldwide, and the lack of available treatments can be in part owed to the difficulty of studying the complexity of the human tear film. The tear film is a several micron thick multilayer structure that resides above the corneal epithelial surface of the eye and consists of an innermost mucin layer, an aqueous layer containing mucins in solution, and an outermost lipid layer that resists evaporation. These components act together to maintain tear film hydration and stability, and this interplay is key to maintaining clear vision and ocular health.

Though few effective treatments exist for DED patients, one molecule that has shown promise in addressing DED symptoms in clinical trials is recombinant human lubricin, a mucin-like glycoprotein that protects the ocular surface. Using a previously developed interferometry-based instrument called the Interfacial Dewetting and Drainage Optical Platform (i-DDrOP), we can create acellular model tear films in vitro to study the effect of recombinant human lubricin on tear film stability. Measurements made using the i-DDrOP capture the rich spatiotemporal behavior of these thin films, and from these data we extract important yet simple-to-use parameters through a robust analysis pipeline. Specifically, from the wetted area fraction evolution plot, we can obtain (i) the evaporative break-up time (EBUT), which represents how quickly the onset of evaporation-driven film instability occurs, and (ii) the wetted area fraction at ten minutes (A10), which represents the thin film’s ability to keep the model ocular surface hydrated over time.

To demonstrate the method’s ability to assess tear film stability in the presence of DED treatments, we quantified the effect of recombinant human lubricin on wetted area fraction evolution. Our data corroborates previously published trends showing that higher lubricin concentrations are better able to stabilize the tear film against evaporation and breakup. We then compared the efficacy of unstressed recombinant human lubricin samples to that of stressed lubricin samples in response to variations in pH and temperature. We were able to capture differences in thin film evaporative breakup and ability to maintain hydration between these samples using the EBUT and A10 parameters described above. In addition to elucidating differences in performance among samples, we show that there exists a threshold concentration at which thin films of recombinant human lubricin solution are able to resist evaporation-driven instability and maintain a wetted curved surface. By providing a facile way to quantify and compare the effect of recombinant human lubricin samples on thin film stability, we hope that these metrics will ultimately help elucidate the mechanism by which recombinant human lubricin protects the ocular surface.