Compressed Wavefront Aberrometry of the Human Eye

Abstract

 

Purpose

 

Shack-Hartmann wavefront sensors (SHWFS) are widely used in ocular measurements and form the basis for modern ophthalmic adaptive optic systems. Currently, SHWFSs are limited in speed by the camera hardware, which is required to collect thousands of pixels per wavefront. Extending the theoretical work of Rostami et al. [1], we have developed a novel algorithm tailored to the human eye that reduces the number of lenslets required to characterize an ophthalmic wavefront, allowing for fewer pixels on the camera to be recorded. The algorithm, named sparse Zernike representation (SPARZER), offers a potential increase in wavefront sensing speed with minimal error in aberration correction. Higher performance wavefront sensing technology could potentially lead to faster and/or wider field adaptive optic systems.

 

Methods

 

The SPARZER algorithm was tested on experimental wavefront data obtained using an aberrometer that incorporated a deformable mirror (DM). The DM coefficients were set to model the typical aberrations reported for human eyes [2]. After reflecting from the DM, the aberrated wavefront was acquired by a commercial SHWFS (Imagine Eyes, FR). Experimental measurements made by the SHWFS were down sampled digitally to a fraction of the total lenslet data. The sparsely sampled data was reconstructed using SPARZER and compared to the full wavefront measurement as well as data reconstructed with linear and spline interpolations.

 

Results

 

For all tested compression ratios, SPARZER performed more accurate aberration measurements than the interpolation methods (Fig. 1). As few as 15 total lenslets (3% of the lenslets used in a full measurement) resulted in an error in defocus of 0.06 D, in astigmatism of 0.20 D and an RMS wavefront error of 0.03 μm over the first 37 Zernike terms.

 

Conclusions

 

Existing SHWFSs can be modified to subsample the number of lenslets required to measure the aberrations of a typical human eye, permitting a potential increase in the speed of wavefront acquisition. Extrapolating the results reported here, using as few as 15 lenslets could result in an accurate aberrometry measurement at speeds exceeding 20 kHz. 1. M. Rostami et al., IEEE T Imag Proc 21, 3139 (2012). 2. J. Porter et al., J Opt Soc Am A 18, 1793 (2001).

 

 

Fig. 1. Log plots of error in defocus (top) and astigmatism (bottom) for ophthalmic wavefronts reconstructed with SPARZER, linear and spline interpolations. The total lenslets used in the full data set is 485.

 

Keywords: 626 aberrations • 676 refraction • 630 optical properties