title: Zone I of Tear Microdesiccates Is a Lipid-Containing Structure.
abstract: OBJECTIVE
  Morphological features of tear microdesiccates on glass surfaces have been associated with tear fluid status. Tear-film lipids play a critical role in the pathophysiology of some ocular surface disorders. Tear microdesiccates display 4 distinctive morphological domains (zones I, II, III, and transition band). In this study, we investigated the lipid location in tear microdesiccates.
  
  
  METHODS
  Tear from individual healthy eyes (assessed by symptoms, signs, and slit-lamp examination) was collected using absorbing minisponges. One-µL aliquots were allowed to dry under ambient conditions on microscope slides. Tear microdesiccates were examined by various transmitted light microscopy methods. Tear lipids were located both by partition experiments using 2 lipophilic dyes (Oil red O and Nile blue A) mixed with tear fluid under conditions preserving morphological features of microdesiccates and by assessing the effect of 2 solvents markedly differing in polarity (water and ethanol) on the morphology of particular domains of preformed microdesiccates.
  
  
  RESULTS
  During desiccation, both Nile blue A and Oil red O became preferentially located in the outermost domain of tear microdesiccates (zone I) without affecting the formation of major fern-like crystalloids (zones II and III). Low volumes of water drastically affected fern-like crystalloids, whereas the gross morphology of zone I was maintained. Contrarily, ethanol, a less polar solvent, was a fixative for fern-like crystalloids, although it markedly affected the bulk of zone I by extracting liquid droplets out of microdesiccates and visibilizing some filamentous subcomponents.
  
  
  CONCLUSIONS
  Zone I is a hydrophobic domain, whereas zones II and III are highly hydrophilic domains of tear microdesiccates. Zone I represents a lipid-rich structure.
authors.affiliation: *Program of Cellular and Molecular Biology, Faculty of Medicine-ICBM, University of Chile, Santiago, Chile; and †Tear Fluid and Ocular Surface Laboratory, Fundación Oftalmológica Los Andes Ophthalmology Clinic (FOLA), Santiago, Chile.
authors.forename: Felipe
authors.initials: F
authors.lastname: Traipe
authors.forename: Leonidas
authors.initials: L
authors.lastname: Traipe
authors.forename: Daniela
authors.initials: D
authors.lastname: Salinas-Toro
authors.forename: Daniela
authors.initials: D
authors.lastname: López
authors.forename: Felipe
authors.initials: F
authors.lastname: Valenzuela
authors.forename: Claudio
authors.initials: C
authors.lastname: Pérez
authors.forename: Cristian
authors.initials: C
authors.lastname: Cartes
authors.forename: Francisca
authors.initials: F
authors.lastname: Zuazo
authors.forename: Patricia
authors.initials: P
authors.lastname: Varela
authors.forename: Héctor
authors.initials: H
authors.lastname: Toledo-Araya
authors.forename: Remigio
authors.initials: R
authors.lastname: López-Solís
mesh_terms: D000293:Adolescent; D001391:Azo Compounds / Q000494:pharmacology; D004396:Coloring Agents / Q000494:pharmacology; D003890:Desiccation; D005260:Female; D064368:Healthy Volunteers; D006801:Humans; D008055:Lipids / Q000032:analysis*; D008297:Male; D010078:Oxazines / Q000494:pharmacology; D013666:Tears / Q000737:chemistry* / Q000187:drug effects; D055815:Young Adult
chemical_list: D001391:Azo Compounds; D004396:Coloring Agents; D008055:Lipids; D010078:Oxazines; C008619:Nile Blue; C011049:oil red O