Purpose. To manufacture and test a set of phase plates for the calibration of ocular aberrometers
and eventually to apply it to the calibration of an ocular laser ray tracing aberrometer.
Methods. The set of phase plates is made by a grey-scale single-mask photosculpture in photoresist
method. Each plate induces a given amount of a particular aberration (Zernike) mode. The set
contains two subsets: (1) different pure Zernike modes to test the accuracy among different orders
(from 3rd to 7th, about 0.3 - 0.4 microns); and (2) plates having different amounts of the same mode,
3rd order coma ranging from 0.11 to 0.47 microns. Right after manufacturing, the plates were tested
twice, as a cross-check, 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. We found a close agreement between the three types of measurement. The maximum
difference between H-S and LRT measurements was 0.032 μm (that is about λ/20, half of the
typical measuring error in human eyes). This permitted us to detect 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 allowed us to discover a small bias, that is almost impossible to
detect working with human eyes or trial lenses. This type of calibration tool is especially important
in clinical environments.This work has been partially supported by the Comisión Interministerial de Ciencia y Tecnología
(Spain), under grant DPI2002-04370-C02.Peer reviewe
