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Olof Sterner, Samuele Tosatti, Charles Scales, Rudolf Aeschlimann, Tawnya J Wilson, Kathrine O Lorenz; Determining the Frictional Energy of 1-day Contact Lens Wear. Invest. Ophthalmol. Vis. Sci. 2016;57(12):1484.
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© ARVO (1962-2015); The Authors (2016-present)
Few in vitro tools exist to simulate the effects of wear on contact lens (CL) material lubricity (CLml) despite the suggested predictive potential of lubricity on end-of-day (EOD) comfort. Additionally, an obstacle in the evaluation of CLml is the difficulty in assigning a coefficient of friction to soft-soft and soft-hard contacts since the ratio of lateral-to-normal forces may not be constant. The purpose of this study was to evaluate whether the lubricity of two commercially available CL materials were altered after exposure to in vitro ageing, and in addition to derive a novel strategy to represent CLml devoid of presumptions regarding linearity in the lateral-to-normal force ratio.
To simulate CL wear, senofilcon A (ACUVUE Oasys 1-day) (AO) and delefilcon A (DAILIES Total 1) (DT1) CLs were cycled for different times (0/2/6/14 and 18 h) between a tear-like fluid (TLF) and air at 20 seconds intervals to mimic the effect of the opening and closing phase of a blink. The tribological properties were characterized using an extended micro-tribometer of that presented by Roba et al. in 2011. Mucin-coated glass counter surfaces in TLF were used for all measurements. An optical microscope was used to determine the effective contact area between counter surface and CL. The applied normal force range varied between 0.25 and 4.0 mN with a stroke length of 1.0 mm at a speed of 0.1 mm/s. CLml was quantified in terms of the average of a non-linear equation fitted to the lateral vs normal force data, multiplied with a sliding distance of 2 mm and reported in units of energy i.e. frictional energy.
The frictional energy (mean ± 95% CI) expended during sliding the counter-surface across the AO lens increased marginally from 66±7 nJ to 86±11 nJ after 18 h of simulated wear, while the frictional energy for DT1 increased from 71±8 nJ to 610±75 nJ during the same time interval.
The lubricity of two CL materials has been found to be susceptible to in vitro ageing, albeit to a significantly different extent. A decrease in CLml with ageing may have clinical implications in terms of reduced EOD comfort. Frictional energy is proposed as a single figure-of-merit of CLml.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
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