title: Spontaneous Blinking from a Tribological Viewpoint.
abstract: The mechanical forces between the lid wiper and the ocular surface, and between a contact lens and the lid wiper, are reported to be related to dry eye symptoms. Furthermore, the mechanical forces between these sliding partners are assumed to be related to the ocular signs of lid-wiper epitheliopathy (LWE) and lid-parallel conjunctival folds (LIPCOF). Recent literature provides some evidence that a contact lens with a low coefficient of friction (CoF) improves wearing comfort by reducing the mechanical forces between the contact lens surface and the lid wiper. This review discusses the mechanical forces during spontaneous blinks from a tribological perspective, at both low and high sliding velocities, in a healthy subject. It concludes that the coefficient of friction of the ocular surfaces appears to be strongly comparable to that of hydrophilic polymer brushes at low sliding velocity, and that, with increased sliding velocity, there is no wear at the sliding partners' surfaces thanks to the presence of a fluid film between the two sliding partners. In contrast, in the case of dry eye, the failure to maintain a full fluid film lubrication regime at high blinking speeds may lead to increased shear rates, resulting in deformation and wear of the sliding pairs. These shear rates are most likely related to tear film viscosity.
authors.affiliation: Dr. Heiko Pult, Optometry & Vision Research, Weinheim, Germany; Cardiff University, School of Optometry & Vision Sciences, Cardiff, UK; Ophthalmic Research Group, Life and Health Sciences, Aston University, Birmingham, UK. Electronic address: ovr@heiko-pult.de.
authors.forename: Heiko
authors.initials: H
authors.lastname: Pult
authors.affiliation: SuSoS AG, Duebendorf, Switzerland.
authors.forename: Samuele G P
authors.initials: SG
authors.lastname: Tosatti
authors.affiliation: Laboratory for Surface Science and Technology, Department of Materials, ETH Zurich, Zurich, Switzerland.
authors.forename: Nicholas D
authors.initials: ND
authors.lastname: Spencer
authors.affiliation: Dioptic GmbH, Weinheim, Germany.
authors.forename: Jean-Michel
authors.initials: JM
authors.lastname: Asfour
authors.affiliation: ZF Friedrichshafen AG, Friedrichshafen, Germany.
authors.forename: Michael
authors.initials: M
authors.lastname: Ebenhoch
authors.affiliation: University of Waterloo, School of Optometry & Vision Science, Waterloo, Canada.
authors.forename: Paul J
authors.initials: PJ
authors.lastname: Murphy
mesh_terms: D001767:Blinking / Q000502:physiology*; D003228:Conjunctiva / Q000378:metabolism*; D003263:Contact Lenses, Hydrophilic; D015352:Dry Eye Syndromes / Q000378:metabolism / Q000503:physiopathology / Q000628:therapy; D006801:Humans; D009077:Mucins / Q000378:metabolism*; D013666:Tears / Q000378:metabolism*
chemical_list: D009077:Mucins
keywords: blinking; coefficient of friction; contact lens; lid wiper; tear film; tribology; viscosity