Shack-Hartmann analysis of multifocal contact lenses

Pete Kollbaum

Abstract

Purpose Complex optical profiles and multiple small optical zones are common features of modern multifocal contact lenses (CL). Characterizing such optics with sampling-based Shack-Hartmann (SH) aberrometry poses significant challenges. We examine the ability of a SH aberrometer to accurately quantify multifocal CLs.
Methods Wavefront errors introduced by multifocal lenses were examined with a single pass SH aberrometer with 150 micron sampling (ClearWave, AMO Wavefront Sciences). Power maps were generated from three lenses: a five concentric zone design, a two-zone aspheric CL design, and a custom made true zonal bifocal. Constrained annular sub-apertures from these lenses were also measured. A polynomial fitting approach (Zernike) for the full multi-zone or sub-apertures and a zonal wavefront reconstruction method which avoids polynomial smoothing were employed.
Results For a 7mm outer pupil diameter power measurements for annular pupils with inner diameters up to 6mm were accurate (0.25D. These errors are exaggerated with fewer orders (e.g. up to 1.9 D error for a 2D add bifocal for a 4th order fitting). Zonal fitting avoided these systematic biases and captured the abrupt power transitions but introduced local fluctuations in power.
Conclusion Our data confirm that even high sampling density SH aberrometers can fail to capture optical characteristics small zones (<1mm) such as those employed in 5-zone multifocals. However using zonal fitting methods we are able to capture abrupt local power changes and quantify zone geometry and power for most multifocal designs.

Details

Year: 2016

Program Number: 160114

Author Affiliation: Indiana University School of Optometry

Co-Authors: Renfeng Xu, Huachun Wang, Basal Altoaimi, Arthur Bradley

Co-Author Affiliation: Indiana University School of Optometry, Indiana University School of Optometry, Indiana University School of Optometry, Indiana University School of Optometry

Room: 211 AB