Validation of a method for measuring small color differences in pigmented contact lenses

A method for measuring and quantifying color variability of soft contact lenses is presented in this paper. The lenses studied are opaquely pigmented, varying in color intensity in each of four hues. The instrument selected for color measurement is the HunterLab ColorQUEST reflectance spectrophotometer using integrating sphere geometry and a customized contact lens support. Total color difference is measured using the Commission International de l'Eclairage (CIE), 1976 L* a* b* color space in delta-E* units. The correlation between the instrumental measurement and human estimation of color intensity difference is presented graphically for each hue. Trained inspectors ranked the eight lenses per hue from lightest to darkest on a linear scale which was converted to the instrumental delta-E* units. The instrument validation is based upon (1) maximum average differences of less than 1.1 delta-E* between the instrument and inspectors, and (2) overall repeatability (SD) of +/- 0.1 for the instrument vs. +/- 0.3 for the inspectors.