Measurement of peripheral wavefront aberrations in the human eye with a Hartmann-Shack sensor

This diploma thesis is a description of the development of a lab set-up and a matlabprogram for measuring wavefront aberrations in the peripheral region of the human eye with a Hartmann-Shack sensor. The purpose is to investigate the optics of the eye in large angles from the visual axis and to help people with a loss of central vision to better utilize their remaining visual field. In the lab set-up a narrow laser beam is sent into the eye, reflected by the retina and propagated back through the optics of the eye. The emerging refracted wavefront is curved and deformed by aberrations in the eye. A Hartmann-Shack wavefront sensor is used to measure the shape of the wavefront. The sensor consists of an array of small lenses where each lens images a small portion of the wavefront onto a spot on a CCDchip. When the wavefront is deformed the spots on the CCD-chip will move away from their corresponding lens-centres. A matlab-program then calculates the wavefront aberrations from the movement of the spots. The algorithm consists of a filtering method with Fourier transformation to locate the spots, an extrapolation with B-spline polynomials to solve the unwrapping problem (how far a spot has moved from its lens-centre) and a least-square fit with Zernike polynomials to calculate the shape of the wavefront and thus the aberrations of the eye. The measurement set-up was calibrated using spherical wavefronts with a maximum error of ± 1.64 mm. Finally some eye measurements in oblique angles in a human eye were performed. The set-up gives sharp images and the program is successful in finding and unwrapping the spots, but the calculated aberrations in the peripheral vision contain some uncertainties due to the elliptic shape of the pupil in large angles.