A direct technique for calculating the profile of aberration of the eye measured by a modified Hartmann-Shack apparatus

We propose a direct numerical method to reconstruct the aberration curve from a set of measured spots, without passing through a wavefront fit. The method is quick and does not require precise knowledge of the position of the pupil center of the human eye. The maximal value of aberration can be estimated even in extreme situations, where the amount of the aberration is large enough that some spots are shifted into areas where other spots are expected. The numerical method also simplifies the discussion of the accuracy and the limitations of the measurement. In addition to the conventional Hartmann-Shack sensor, the direct method is applied to a modified version of this apparatus. In the modified optical setup, losses and noise are reduced, and a well-defined optical pattern is detected so that no image processing - which generally includes subjective decisions - is necessary. The apparatus offers the flexibility of choosing several magnifications of the wavefront reflected by the retina (photosensitive membrane of the eye), without changing any element of the setup. The accuracy and the limitations of the apparatus are discussed, and practical applications are illustrated. (C) 2000 Elsevier Science B.V. All rights reserved.