The Conjunctiva

The conjunctiva is a mucous membrane that covers the majority of the ocular surface and is vital to the health of the eye as a whole. The conjunctival and limbal epithelium are derived from surface ectoderm during embryologic development. The conjunctiva extends from the mucocutaneous junction (MCJ) at the lid margins to the limbus adjacent to the cornea. The MCJ is the junction between hydrophobic (unwettable) epidermis and hydrophilic (wettable) conjunctiva and is defined by the anterior apex of the tear film meniscus. The corneoscleral limbus is a unique stem cell niche microenvironment that supports a population of pluripotent limbal stem cells, which continuously regenerates the clear epithelium of the cornea throughout life. Injury to the limbus and loss of limbal stem cells result in poor epithelialization and progressive conjunctivalization of the cornea. The conjunctiva plays a critical role in the maintenance of a healthy tear film. Conjunctival goblet cells secrete MUC5AC, the primary constituent of the tear mucin layer. Conjunctival epithelial cells express membrane-bound mucins (MUC1, MUC4, MUC16), which confer wettability to the ocular surface. The conjunctiva also modulates the volume, osmolarity, and electrolyte concentration of the tear film and contributes significantly to basal tear secretion.