Corneal mucous plaques are abnormal collections of a mixture of mucus, epithelial cells, and proteinaceous and lipoidal material that adhere firmly to the corneal surface. The plaques also may enmesh calcareous granules and bacteria, as well as dust particles and other foreign bodies. The mucous plaques are translucent to opaque and may vary in size and shape from multiple small islands to bizarre patterns that may involve more than one half the corneal surface. 
An abnormality of the exposed surface of the superficial corneal epithelial cells, excessive mucous formation, and the presence of epithelial receptor sites for the plaque elements predispose to this condition. The normal desquamation of epithelial cells beneath the plaque is retarded, and exfoliating face cells may become incorporated in the plaque. The plaque is formed when high viscosity mucus and proteinaceous material become adherent to the deeper squamous cells of the cornea or even to the Bowman layer through the intercellular spaces, as well as through abnormally formed transcellular aperture and epithelial defects; because of its physiochemical property, the mucous plaque enmeshes the desquamated epithelial cells.
Mucous viscosity may increase as a result of dehydration, an increase in the sialomucin component, or secondary to staphylococcal infection with subsequent liberation of enzymes that lyse the mucoprotein and mucopolysaccharide components of mucus normally produced by conjunctival goblet cells.
Corneal mucous plaques are seen primarily in patients with keratoconjunctivitis sicca.
Eye pain can be present while the plaques are present.
Keratitis sicca is more common in women than in men.
The incidence of keratitis sicca increases with age.