We investigate the rupture mechanism of a precorneal thin mucus coating sandwiched between the aqueous tear film and the corneal epithelial surface with a monolayer of surfactant overlying the aqueous layer. The Ostwald constitutive relation is employed to model mucus rheology and a linear equation of state describing the relationship between surface tension and surfactant concentration is adopted. Five coupled equations governing the transport of surfactant, mucus and total liquid layer thicknesses, based on lubrication theory, have been derived. The resulting equations are solved numerically in order to explore the effect of system parameters such as mucus rheology, aqueous-mucus thickness ratio, aqueous-mucus interfacial tension and Marangoni number on tear film evolution in the presence of van derWaals forces, which could induce film rupture.