An improved Hartmann-Shack wavefront sensor for ocular aberrometry using wavefront slope and curvature measurements

Abstract

The Hartmann-Shack wavefront sensor (HS) conventionally used in measuring the optical aberrations of the human eye estimates the slopes of the wavefront with a spatial resolution limited by the microlens size. We propose to use the HS sensor in a novel way to extend its accuracy for a given resolution by estimating the curvature of the wavefront over the face of each lenslet. This is achieved by capturing HS data images at two axial locations. The intensity differences between corresponding spots can be used to compute wavefront curvature (i.e. the local lapalacian) using the transport-of-intensity equation under the approximation that the spatial intensity distribution is almost constant over the face of a microlens. A novel algorithm of wavefront reconstruction combines the slope and curvature in two steps: 1) Implementation of a first variational least squares scheme. 2) Simultaneous solution of two partial differential equations with two boundary conditions. Results from computer simulations demonstrate that increased accuracy in wavefront reconstruction depends on wavefront characteristics, noise and sampling density of the lenslet array.