Surface roughness and refractive index changes in contact lens induced by lens care systems.

PURPOSE: The aim of this study was to analyze the influence of different lens care systems in surface roughness and refractive index (RI) of contact lenses (CL). This information provides us with a better understanding of how care solutions affect CL materials. METHODS: Several CL and three commercially available and appropriate lens care solutions were used (two polyhexamethylene biguanide and one hydrogen peroxide care systems). Lenses were immersed in the lens care systems, and then measurements with CLR 12-70 digital automated refractometer and atomic force microscopy analysis on Tapping mode were recorded. The measurements were performed before and after the lenses were immersed in each care solution. RESULTS: Significant changes were observed on the CL materials when exposed to lens care systems. All the materials changed, to a greater or lesser extent, their roughness and RI, after being immersed in the different solutions. The water content varied between 0% (Nelfilcon A in ReNu Multiplus, Senofilcon A in AOSEPT Plus, and Methafilcon A in Solocare Aqua) and 4.1% (Hilafilcon B in Solocare Aqua) The higher change in roughness was obtained with ReNu Multiplus in the lens Comfilcon A (with an increase of 27.2 nm) and Senofilcon A (with an increase of 16.7 nm). CONCLUSION: This study suggests that lens care systems play an important role in surface roughness and RI of CL.

New electronic implementation of the timestamps method intended for high resolution comparison of laser wavelengths.

This article describes a new measurement system for the comparison of two electronic signals of different frequencies with application to high resolution comparison of laser wavelengths using a Michelson interferometer. It was built within the framework of research projects made by the University of Vigo and the Laboratorio Oficial de Metroloxía de Galicia (LOMG) in cooperation with Escolas Proval High School. The new hardware is based on a cheap high-speed module for the acquisition of data and a microcontroller module for processing, which can also be used for practical lessons in vocational training. The system has been tested with electronic signal generators. The novel measurement method reduces the uncertainty using multiple consecutive measurements and the fractional part of the fringes and could achieve precisions in the range 10-12 of the wavelength ratios.