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Samuele Tosatti, Rudolf Aeschlimann, Kathrine E Lorenz, Danielle Boree, Joseph Kakkasseri; Dynamic Coefficient of Friction of Limbal Ring Contact Lenses. Invest. Ophthalmol. Vis. Sci. 2014;55(13):4653.
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© ARVO (1962-2015); The Authors (2016-present)
To evaluate the coefficient of friction (CoF) of limbal ring contact lenses in the central (optical zone) and peripheral (pigmented) areas of the lens.
Two limbal ring contact lens types [1-DAY ACUVUE® DEFINE® (AD) and Eye Coffret (EC)] were investigated in the center (C) and in the peripheral pigmented (PP) area of both front (FS) and back surface (BS) of the lens. CoF was measured with the lens in a tear-like fluid (TLF) using a Basalt MUST micro-tribometer and a mucin coated counter surface (Roba et al). To ensure consistent contact geometry, a tilted hemispherical sample support holder was used for the PP measurements. Statistical analysis comparing the PP and C portions of the lens on both the front and back surfaces was completed using a linear mixed model for repeated measures. 95% confidence intervals (CI) for the difference between areas type (PP-C) were constructed within each combination of lens brand and surface type. Similarly, 95% CIs for the difference between brands (EC-AD) were constructed within each combination of area and surface type. All intervals were adjusted for multiplicity using simulation methods.
For EC, there was a statistically significant difference between the C and PP areas of the lens on both the front and back surface (FS CI=(-0.124, -0.016) p-value=0.015; BS CI=(0.419, 0.526) p-value<0.001). No statistical significant difference was found between the C and PP areas of AD and these areas were equivalent within a 0.06 CoF margin (FS CI (-0.058, 0.049) p-value=0.859; BS CI (-0.048, 0.052) p-value=0.922). AD was found to have a lower CoF than EC on both the FS and BS in both the C and PP areas (FS C CI=(0.079,0.205) p-value<0.001;PP CI=(0.014,0.139) p-value=0.015);(BS C CI=(0.062,0.187) p-value<0.001;PP CI=(0.535,0.665) p-value<0.001).
It is possible to measure dynamic CoF in different areas of limbal ring lenses. Depending on the lens type tested, differences in CoF may be seen between the C and PP regions. These differences may be attributed to the differences in surface roughness and the presence of pigments on the lens surface or enclosed within the lens matrix.
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