title: Friction Measurements on Contact Lenses in a Physiologically Relevant Environment: Effect of Testing Conditions on Friction.
abstract: OBJECTIVE
  To characterize the effect of lubricant composition and in vitro ageing on the coefficient of friction (CoF) of a wide range of commercially available soft contact lenses (SCLs).
  
  
  METHODS
  The CoF of SCLs was characterized by means of microtribometry against a mucin-coated glass disk. One reusable (RU) silicone-hydrogel (SiHy) lens, senofilcon A, and two daily disposable (DD) lenses, etafilcon A (hydrogel) and nelfilcon A (hydrogel), were tested under different lubricant solutions, including a tear-like fluid (TLF) containing proteins and lipids. Five RU (balafilcon A [SiHy], comfilcon A [SiHy], etafilcon A [hydrogel], lotrafilcon B [SiHy], senofilcon A [SiHy]) and five DD (delefilcon A [SiHy], etafilcon A [hydrogel; two lens types], narafilcon A [SiHy], nelfilcon A [hydrogel]) lenses were tested before and after exposure to an in vitro ageing process, consisting of continuous immersion and withdrawal from TLF for 18 hours. The CoF in TLF was further compared to previously published data collected in a different lubricant.
  
  
  RESULTS
  After in vitro ageing, three RU (balafilcon A, etafilcon A, comfilcon A) and three DD (delefilcon A, etafilcon A, nelfilcon A) lenses displayed a significant increase in CoF (P < 0.05). Lenses that contained poly (vinyl pyrrolidone; PVP) showed unaltered CoF after ageing.
  
  
  CONCLUSIONS
  An in vitro methodology to simulate in vivo wearing of contact lenses has been proposed. The results suggest that certain lens materials show increased CoF after ageing, with potential clinical implications. The results indicate that the presence of a persistent wetting agent is of advantage to maintain a low CoF after prolonged wearing.
authors.affiliation: SuSoS AG, Dübendorf, Switzerland.
authors.forename: Olof
authors.initials: O
authors.lastname: Sterner
authors.affiliation: SuSoS AG, Dübendorf, Switzerland.
authors.forename: Rudolf
authors.initials: R
authors.lastname: Aeschlimann
authors.affiliation: SuSoS AG, Dübendorf, Switzerland 2Laboratory for Surface Science and Technology, Department of Materials, ETH Zurich, Zurich, Switzerland.
authors.forename: Stefan
authors.initials: S
authors.lastname: Zürcher
authors.affiliation: Johnson & Johnson Vision Care, Inc., Jacksonville, Florida, United States.
authors.forename: Kathrine
authors.initials: K
authors.lastname: Osborn Lorenz
authors.affiliation: BetaLogics Venture, Janssen R&D LLC, Raritan, New Jersey, United States.
authors.forename: Joseph
authors.initials: J
authors.lastname: Kakkassery
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: SuSoS AG, Dübendorf, Switzerland.
authors.forename: Samuele G P
authors.initials: SG
authors.lastname: Tosatti
mesh_terms: D003263:Contact Lenses, Hydrophilic; D004867:Equipment Design; D017276:Friction; D006801:Humans; D065346:Lubricant Eye Drops / Q000494:pharmacology; D008422:Materials Testing / Q000379:methods*; D013666:Tears / Q000378:metabolism*
chemical_list: D065346:Lubricant Eye Drops