Pros and Cons of soft contact lens power mapping

Abstract

Purpose. To provide an overview of currently available meth- ods and instruments for the measurement of soft contact lens power maps, together with their advantages and potential shortcomings. Material and Methods. The three leading measurement prin- ciples of Moiré Fringe, Shack-Hartmann and Phase Shifting Schlieren were identified, and the relevant literature reviewed and technical specifications summarised. To demonstrate some of the potential deficiencies associated with optical power mapping, a series of measurements were conducted on toric, multifocal and extended depth of focus lenses, using one representative instrument. Raw measured data were analysed using various analysis tools and parameters. Results. Power maps and power profiles are presented for the various lens types. Different smoothing filter settings resulted in significantly different power profiles near the optical centre. The ‘Power versus Azimuth’ profiles showed unexpected results. Conclusion. While all three methods are generally reliable and easy to use, there are still some limitations which need to be considered when interpreting the results. In particular, the profile filter settings need to be chosen carefully for multifocal and extended depth of focus lenses. The need for accurate refractive index data for lens material and solution was demonstrated. Keywords Soft contact lenses, power maps, power profiles, Moiré Fringe, Shack-Hartmann, Phase Shifting Schlieren