June 2013
Volume 54, Issue 15
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ARVO Annual Meeting Abstract  |   June 2013
A New Paradigm for the Structure of the Tear-Film Lipid Layer
Clayton Radke; Liat Rosenfeld; Colin Cerrretani; Danielle Lieske; Michael Toney
Author Affiliations & Notes
  • Clayton Radke
    chemical and biomolecular engineering, university of california, berkeley, CA
    vision science group, university of california, berkeley, CA
  • Liat Rosenfeld
    chemical engineering, stanford university, stanford, CA
  • Colin Cerrretani
    chemical and biomolecular engineering, university of california, berkeley, CA
  • Danielle Lieske
    chemical engineering, stanford university, stanford, CA
  • Michael Toney
    stanford synchrotron radiation light source, SLAC national accelerator laboratory, menlo park, CA
  • Footnotes
    Commercial Relationships Clayton Radke, novartis corporation (F); Liat Rosenfeld, None; Colin Cerrretani, Alcon Corporation (F); Danielle Lieske, None; Michael Toney, None
  • Footnotes
    Support None
Investigative Ophthalmology & Visual Science June 2013, Vol.54, 947. doi:
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      Clayton Radke, Liat Rosenfeld, Colin Cerrretani, Danielle Lieske, Michael Toney; A New Paradigm for the Structure of the Tear-Film Lipid Layer. Invest. Ophthalmol. Vis. Sci. 2013;54(15):947.

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Abstract
 
Purpose
 

We explore the unique rheological and structural properties of human and bovine meibomian lipids (ML) to provide insight into the on-eye physical behavior the human tear-film lipid layer (TFLL).

 
Methods
 

Human ML was collected from healthy individuals. Bovine ML was exuded from freshly excised eyelids. Bulk rheological properties of pooled meibomian lipids were measured by a commercial stress-controlled rheometer; a home-built Interfacial Stress Rheometer (ISR) probed the interfacial viscoelasticity of spread layers of meibomian lipids. Small- and wide-angle X-ray scattering detected the presence and melting of dispersed crystal structures. A differential scanning calorimeter (DSC) analyzed phase transitions in bulk samples of bovine meibum.

 
Results
 

Bulk and interfacial rheology measurements show that meibum is extremely viscous and highly elastic. It is also a non-Newtonian, shear-thinning fluid. Small- and wide-angle x-ray diffraction (SAXS and WAXS), as well as DSC, confirm the presence of suspended lamellar-crystal structures at physiologic temperature. A melt transition is detected in the bulk and interfacial rheology between 29-36 °C. Disappearance of crystalline particles was detected by SAXS, WAXS, and DSC over the same temperature range as that of the melt transition in the rheological measurements.

 
Conclusions
 

The TFLL is classically thought to be a parallel stack of molecular layers. Based on our new findings, the proposed structure for the TFLL shown at physiologic temperature in Fig. 1 is a highly viscoelastic, shear-thinning liquid suspension consisting of lipid lamellar crystallites immersed in a continuous liquid phase with no long-range order. The duplex lipid film exhibits two separate interfaces, air/lipid and water/lipid, with aqueous protein and surfactant-like lipids adsorbed at the water/lipid surface. Minor amounts of water and protein are present in the film. This new picture of the TFLL overturns the current accepted viewpoint.

 
Figure 1. Schematic of the TFLL. At eye temperature, asymmetric crystallites (mostly phase A) are dispersed within an isotropic, viscoelastic continuous liquid. Polar lipids orient at the aqueous/lipid interface, but orientation does not persist deep into the bulk lipid layer. Drawing is not to scale.
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Figure 1. Schematic of the TFLL. At eye temperature, asymmetric crystallites (mostly phase A) are dispersed within an isotropic, viscoelastic continuous liquid. Polar lipids orient at the aqueous/lipid interface, but orientation does not persist deep into the bulk lipid layer. Drawing is not to scale.
 
Figure 1. Schematic of the TFLL. At eye temperature, asymmetric crystallites (mostly phase A) are dispersed within an isotropic, viscoelastic continuous liquid. Polar lipids orient at the aqueous/lipid interface, but orientation does not persist deep into the bulk lipid layer. Drawing is not to scale.
Figure 1. Schematic of the TFLL. At eye temperature, asymmetric crystallites (mostly phase A) are dispersed within an isotropic, viscoelastic continuous liquid. Polar lipids orient at the aqueous/lipid interface, but orientation does not persist deep into the bulk lipid layer. Drawing is not to scale.
View OriginalDownload Slide
 
Keywords: 486 cornea: tears/tear film/dry eye • 480 cornea: basic science  
© 2013, The Association for Research in Vision and Ophthalmology, Inc., all rights reserved. Permission to republish any abstract or part of an abstract in any form must be obtained in writing from the ARVO Office prior to publication.
Copyright © 2025 Association for Research in Vision and Ophthalmology.
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