Some Optical Considerations of Synthetic Hydrogel Polymers for Contact Lens Usage

Abstract

The accurate measurement of hydrogel contact lenses presents a number of problems. The inherent flexibility of the material and its similarity to saline, in terms of refractive index, make measurements unpredictable and difficult. The aim of the experimental work was to develop an accurate method for measuring the radii of curvature, thickness and refractive index of hydrogel contact lenses. The construction of novel apparatus allowed interference patterns to be generated using a Linnik micro-interferometer. The generated patterns were analysed and the radii of curvature of a series of Bausch and Lomb SOFLENSES were calculated to an accuracy of 10-3 mm. The experimental results showed a good agreement with the theoretical results published by the manufacturer. The micro-interferometer was also employed to determine the refractive index of a range of hydrogel materials. The spherical aberration of SOFLENSES in air and in situ on the human eye was investigated using a commercially available photoelectric keratoscope, the "PEK" system 2000. The results present a comprehensive view of the changes in the lens parameters when applied to the cornea.