Patterns of mucin adherence to contact lenses

Contact lens wear alters the preocular fluid through factors that include tear deposits on the lens. In the current study, lens-adherent material was extracted to assess whether contact lenses sample mucins from the preocular fluid.

Discarded extended-wear contact lenses were collected from patients with no ocular surface disease. Mucins were extracted in guanidine hydrochloride (GuHCl) with protease inhibitors. After the supernatant was removed, the extraction was repeated twice with the addition of 10 mM dithiothreitol, making a total of three extractions. Mucins were isolated by cesium chloride (CsCl) gradient centrifugation and size fractionated on Sepharose CL2B. Charge distribution was analyzed on ion-exchange chromatography with a lithium perchlorate (LiClO(4)) gradient.

Contact lens-adherent mucins comprised soluble mucins and mucins that required solubilization by (repeated) dithiothreitol treatment. MUC1, MUC4, MUC2, and MUC5AC mucins eluted mainly at low buoyant densities in extractions from lenses worn long term without disinfection and at successively higher buoyant densities from monthly disposable contact lenses. Mucins with little negative charge, which were observed in all extractions, and very highly negatively charged species, present in the second and third extractions from contact lenses, had no equivalents in tissue-extracted mucins.

Mucins adhering to contact lenses are altered forms of intracellular mucins. Different degrees of adherence of mucins to contact lenses may occur, either because of mucin characteristics or after mucin complexation with adherent materials. In the context of good contact lens hygiene, their presence may offer some protection from toxicants in the tear film, because mucins could function as acceptors for charged moieties such as free radicals.