Purchase this article with an account.
W Sawyer, Juan Uruena, Thomas Angelini, Alison Dunn, John Pruitt; Laboratory Model for Wear of Contact Lenses and Effects on Lens Lubricity of Surface Gel Layers. Invest. Ophthalmol. Vis. Sci. 2013;54(15):493.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
Lubricity of contact lenses is recognized as an important contributor of comfort (Brennan 2009). Experiments aimed at quantifying the lubricity of lenses are traditionally measured on new lenses that have been removed from the package and either gently rinsed in a saline solution or tested in the packing solution directly (Dunn 2013). The purpose of this research is to establish a simple and scalable method to mechanically exercise contact lenses and simulate wear in a controlled laboratory environment, and then to perform lubricity measurements on the front curve surface of the lenses at varying time points of wear.
Poly(HEMA) (60% pHEMA) hydrogels were molded inside of transparent acrylic containers to a thickness of approximately 3 mm. A series of poly(HEMA) spheres of 6 mm diameter were also molded and added to the hydrogel lined cup to a packing fraction of approximately 25%. A single contact lens (delefilcon A) was placed within the ensemble of hydrogel spheres and the container was filled with Phosphate Buffered Saline. The entire collection was shaken at 31 Hz for various time points. Image analysis was used to track the hydrogel spheres and to quantify the collision frequencies. Based on this analysis a mathematical model of mechanical energy and tribological severity was developed and compared to the tribological severity of 1,000 blinks per hour of wear. Prior to friction testing lenses were examined for evidence of wear and damage was quantified using scanning optical microscopy.
This delefilcon A lenses showed a characteristic friction coefficient of mu=0.02, with a standard deviation for each measurement of approximately mu = 0.005. The friction coefficients did not substantially change over the course of the 720 minutes of mechanical wear. Optical microscopy confirmed that the lenses still maintained a surface gel layer.
A simple laboratory method for wearing contact lenses through mechanical agitation was developed and characterized. Even after 720 minutes of simulated wear, the lubricity and surface gel layers were maintained on the delefilcon A lenses. Brennan, AAO 2009. Dunn, et al., Tribology Letters, 2013.
This PDF is available to Subscribers Only