Ocular
mucins are thought to play integral roles in ocular surface lubrication, anchoring of the aqueous, stabilizing the
lipid components of the tear film, eliminating
foreign bodies and pathogens, and with potential involvement in cell cycle mediation and apoptotic activity of ocular surface epithelia. Ocular
mucins are of secreted and membrane-associated types. Secreted
mucins may be of large gel-forming type or small soluble
mucins (e.g., MUC5AC and MUC7). Membrane-associated
mucins such as MUCs 1 and 4 are a major component of the glycocalyx. They are thought to render structural support to the microplicae and mediate epithelial cell cycle and apoptotic activity. The alterations in ocular
mucins with
contact lens wear are unclear. Recent work shows
mucin expression may be up-regulated during the early years of
contact lens wear, and with long-term lens wear,
mucin expression may return to normal levels or sub-normal levels, although this is not well understood. Further, the polar nature of
mucins may be associated with their affinity for
contact lens surfaces making them a component of
contact lens deposition. This has potential implications in the wettability and tolerability of
contact lenses, and may be impacted by surface coatings,
polymer characteristics, or care solutions. Conjunctival
mucin gene expression and secretion may be deficient in several ocular surface disorders associated with
dry eye. Deficiency and alterations in glycosylation characteristics of MUC5AC and MUC2 have been reported in both Sjögren and non-Sjögren
dry eye types. Decreased binding of the membrane-associated
mucin MUC16 to the conjunctival epithelium has been reported in Sjögren
dry eye while MUC1 alterations have been reported in Sjögren and non-Sjögren
dry eye states. In view of the
mucin involvement in
dry eye conditions, stimulation of mucus secretion pathways may hold promise in the
pharmaceutical treatment of
dry eye.