Surface-Chemical Pathways of Corneal Wetting and Defense

Various surface-chemical interactions among the corneal epithelium, ocular mucous gel, tear film and tear film contaminants (e.g., cellular debris, lipids, bacteria) can be characterized based on their apolar and polar (acid-base) surface properties. Based on this approach, the surface-chemical pathways of the tear film breakup and of the corneal epithelial lubrication, cleansing, wetting and defense will be discussed. A strong monopolar repulsion keeps mucus in the form of a highly hydrated gel, which cannot adhere to the normal glycocalix carrying epithelial surface, but forms an effective surface-chemical trap for the apolar and weakly polar hydrophobic contaminants. However, mucus-deficiency and/or a host of epithelial surface abnormalities (e.g., increased cell loss, chemical or morphologic changes, damage) can initiate a vicious cycle comprising of factors such as: increased mucus contamination, loss of mucus and epithelial hydrophilicity, abnormal adhesion and aggregation of mucus, reduced mucus mobility and faulty surface cleansing. All of these factors can conspire to produce a chronically unstable tear film secondary to the loss of corneal surface wettability. I will also present some experimental results on the instability and dewetting of thin liquid polydimethylsiloxane (PDMS) films intercalated between an aqueous medium and a silicon wafer grafted with PDMS brushes. This is a thin film analog of the precorneal thin mucus coating sandwiched between the aqueous tear film and the glycocalyx carrying corneal epithelial surface. Lowering of the PDMS-water interfacial tension by a surfactant results in dewetting even of micrometer thick films within a few minutes.
References related to this presentation:
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