Purpose: To manufacture and test a set of phase plates for the calibration of ocular aberrometers and apply it to the calibration of an ocular laser ray tracing aberrometer.
Methods: The set of phase plates is made by a greyscale single-mask photosculpture in photoresist method. Each plate induces a given amount of a particular aberration (Zernike) mode. The set contains two subsets: 1) pure Zernike modes to test the accuracy among different orders (from 3rd to 7th, approximately 0.3 to 0.4 microm); and 2) plates having different amounts of the same mode, 3rd order coma ranging from 0.11 to 0.47 microm. After manufacturing, the plates were tested twice, as a crosscheck, measuring the aberration pattern of each plate with a Mach-Zehnder interferometer and a single-pass Hartmann-Shack wavefront sensor. The set was then applied to the calibration of an ocular double-pass laser ray tracing aberrometer.
Results: Close agreement was found between the three types of measurement. The maximum difference between Hartmann-Shack and laser ray tracing measurements was 0.032 microm (ie, approximately lambda/20, half of the typical measuring error in human eyes). This permitted detection of a small bias in the ocular laser ray tracing aberrometer.
Conclusions: The calibration set may be a powerful tool for the assessment of accuracy and reliability in ocular aberrometry. It discovered a small bias, which is almost impossible to detect when working with human eyes or trial lenses. This type of calibration tool is especially important in clinical environments.