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Jeffery Schafer, Robert Steffen, Katarzyna A Wygladacz, Charles Lusignan, Daniel Hook, Kristin Simoncelli; Atomic Force Microscopy and Coefficient of Friction Analysis of Unworn and Worn Soft Contact Lenses. Invest. Ophthalmol. Vis. Sci. 2014;55(13):6067.
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© ARVO (1962-2015); The Authors (2016-present)
To evaluate the effect of soft contact lens wear on coefficient of friction (CoF) and atomic force microscopy (AFM) as compared to unworn lenses.
Five healthy adults with normal vision bilaterally wore delefilcon A and nesofilcon A contact lenses in a random order for 4 hours each. For AFM, worn samples were removed and analyzed immediately with the Dimension ICON AFM to characterize the morphology and phase lag. CoF was obtained via TA Instruments DHR3 stress rheometer. Lenses were immersed in BBS, conformed around a 6 mm diameter polished stainless steel ring-shaped rub tool, and allowed to relax until the axial force stabilized at a contact pressure of ~ 2 kPa, similar to eyelid pressure.
Unworn and worn nesofilcon A lenses exhibited a smooth featureless surface (RMS: unworn 1.9 ± 0.2 nm and worn 7.2 ± 3.7 nm). Unworn and worn delefilcon A lenses showed a branched surface coating (RMS: unworn 14.2 ± 5.5 nm and worn 10.9 ± 4 nm). The RMS value for delefilcon A was slightly higher compared to nesofilcon A. Phase lag and topography of worn lenses revealed the presence of deposits on both hydrogels. Static CoF was 0.04 ± 0.01(unworn), 0.14 ± 0.04 (worn) for nesofilcon A versus 0.64 ± 0.14 (unworn), 0.88 ± 0.13 (worn) for delefilcon A. Kinetic CoF 0.25 rad/s , was 0.04 ± 0.01(unworn), 0.06 ± 0.01 (worn) for nesofilcon A and 0.12 ± 0.01 (unworn), 0.13 ± 0.01 (worn) for delefilcon A.
AFM results showed that both hydrogels attracted deposits but the worn nesofilcon A surface morphology appeared more uniform and less altered by wear. Gauged via AFM, delefilcon A attracted more deposits than the nesofilcon A lens as no clear areas were found. Static and low speed kinetic friction showed nesofilcon A has lower friction than delefilcon A for both worn and unworn lenses.
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