title: Lens-care-solution-induced alterations in dynamic interfacial properties of human tear-lipid films.
abstract: OBJECTIVE
  To evaluate the influence of lens care solutions (LCS) on interfacial dynamics and rheological properties of human tear-lipid films.
  
  
  METHODS
  Tear lipids were extracted from Schirmer strips collected from 6 healthy subjects. Sessile bubble tensiometry was used to study interfacial properties at 22°C. Lipids were deposited on an air bubble immersed into electrolytes solution to form 90±20nm films. Lipid films were subjected to expansion-compression cycles for dynamic interfacial properties and to step-strain relaxations for assessments of rheological properties. LCS (BioTrue [BT], PureMoist [PM], Revitalens [RL], ClearCare [CC]) were injected into optical chamber and equilibrated for 2h without or with lipid films. Dynamic interfacial properties of films were measured. Then electrolyte solution was pumped through chamber and properties of films were re-evaluated.
  
  
  RESULTS
  Equilibrium surface tension (EST), elasticity modulus (E), and relaxation times (τ) of tear lipids were 22±2.1mN/m, 10.7-14.8mN/m, and 80-150s, respectively. EST for LCS was 43.6±0.2 for CC, 38.3±0.2 for BT, 36.5±1.2 for RL, and 32.8±0.2mN/m for PM. [corrected]. E for LCS varied within 0.5-6.7mN/m, and τ varied from 49 to 68±5s. For mixed lipids+LCS films, EST remained unchanged whereas E and τ were reduced for all LCS types. Exposure to PM and RL noticeably altered the shape of lipid-film iso-cycles. These changes persisted after LCS washout.
  
  
  CONCLUSIONS
  Some components of LCS bind irreversibly to lipid films and make them less viscous and less elastic. These findings suggest the possibility of tear-film destabilization upon LCS exposure.
authors.affiliation: Clinical Research Center, School of Optometry, University of California at Berkeley, United States.
authors.forename: Tatyana F
authors.initials: TF
authors.lastname: Svitova
authors.affiliation: Clinical Research Center, School of Optometry, University of California at Berkeley, United States. Electronic address: mlin@berkeley.edu.
authors.forename: Meng C
authors.initials: MC
authors.lastname: Lin
mesh_terms: D018639:Contact Lens Solutions / Q000494:pharmacology*; D005260:Female; D006801:Humans; D008055:Lipids / Q000032:analysis*; D008297:Male; D012212:Rheology; D013666:Tears / Q000737:chemistry* / Q000187:drug effects; D055815:Young Adult
chemical_list: D018639:Contact Lens Solutions; D008055:Lipids
keywords: Biophysics; Human tear-film stability; Human tear-lipids; Relaxation mechanisms; Rheology