Tear lipocalin captures exogenous lipid from abnormal corneal surfaces

Abstract

PURPOSE. The cornea is protected by apical hydrophilic transmembrane mucins and tears. In pathologic states the mucin barrier is disrupted, creating potential for meibomian lipids to adhere more strongly. Undisplaced lipids create an unwettable surface. The hypothesis that pathologic ocular surfaces alter lipid binding and the ability of tear proteins to remove lipids was tested. METHODS. Corneas with pathologic surfaces were studied for lipid adhesion and removal by tears. Capture of fluorescencelabeled phospholipids by human tears was assessed by steady state fluorometry. Tear proteins were separated by gel filtration chromatography and analyzed for bound lipids. RESULTS. Contact angle measurements revealed strong lipid adherence to corneas submerged in buffer. Lower contact angles are observed for lipids on completely de-epithelialized corneas compared with intact corneas (P=0.04). Lipid removal from these surfaces is greater with whole tears than with tears depleted of tear lipocalin (P < 0.0005). Significantly fewer lipids are captured by tears from Bowman's layer than from epithelial-bearing surfaces (P < 0.025). The only tear component to bind the fluorescence-tagged lipid is tear lipocalin. The histology of a rare case of dry eye disease demonstrates the dominant features of contemporaneous bullous keratopathy. Lipid sequestration from this cornea by tear lipocalin was robust. CONCLUSIONS. Lipid is captured by tear lipocalin from corneas with bullous keratopathy and dry eye. Lipid removal is slightly abrogated by greater lipid adhesion to Bowman's layer. Reduced secretion of tear lipocalin documented in dry eye disease could hamper lipid removal and exacerbate ocular surface pathology. © Association for Research in Vision and Ophthalmology.