A Two-Phase Model for Mucosal Aggregation and Clearance in the Human Tear Film

This study aims to computationally identify the detailed mechanisms of the adhesion process of mucin and foreign bodies in the human tear film subject to the blinking motion of eyelid. The results give us a clue about the role of mucus as a protective agent for the ocular surface and its role in diseases such as dry eye syndrome (DES). We propose a multi-phase model which models the tear film as an inhomogeneous fluid comprising of a mixture of an aqueous layer in which mucin particles are exponentially distributed in the direction normal to corneal surface. We model the mucin adherence to any immersed foreign object, and its overall clearance through the blinking motion of the eyelid. The motions of mucin in the flow are solved by a force balance equation which accounts for the macroscopic interactions between the fluid and the body. The clearance rates of the foreign particle are explored under various conditions with different varying mechanical properties of mucin such as its adhesion force, distribution profile, as well as its viscosity. Our parametric study shows that a condition for higher clearance rate requires (i) greater mucin population in the entire region of tear film, i.e., larger viscosity, (ii) an optimal mucin distribution profile, and (iii) normal physiologic adhesion force between mucin and immersed particles.