The Fluid Mechanics of the Eye and the Role of the Mucus Layer

We discuss the role of the mucus layer in the eye. The tear film in the eye is composed of a mucus layer, an aqueous layer and a lipid layer. While the aqueous and lipid layers are Newtonian, the mucus layer is non-Newtonian. It is commonly believed that the mucus layer serves as a lubricant for the cornea. However, we hypothesize that it serves a greater purpose as a protective layer from foreign particles; the normal stress effects of a viscoelastic fluid under the blinking motion of the eyelid would act towards pushing out any particle embedded in this layer. To prove this hypothesis, we mathematically study the fluid mechanics of a viscoelastic, shear thinning fluid modeled by a generalized second grade fluid. As a first step, we investigate the flow and stresses induced by a shearing motion (part of a blink cycle) and its effect upon an embedded particle, which is modeled by the Wiberg-Smith equation.