Effect of Higher Order Aberrations on Image Quality in the Human Eye

Though measurements of the wave aberrations of the human eye have been made with several techniques 1-3 , there remains considerable uncertainty about the contribution of higher order aberrations to the optical quality of the human eye 4 . Knowledge of very high order aberrations is important, for example, because they may limit resolution in fundus imaging. We have constructed a wavefront sensor based on the Hartmann-Shack principle 3 to measure the contribution of higher order aberrations in a number of eyes. A point source from a 632.8 nm laser is imaged on the retina and the light reflected from the retina returns through the pupil of the eye. A two-dimensional array of lenslets is conjugate with the eye's pupil, dividing the wavefront exiting the eye into a large number of individual beams. The light from each lenslet is focused on a CCD array, produced an array of spots. Fig. 1a shows the regular array of spots that would have been obtained from a perfect eye with no aberrations; Fig. 1b shows the distorted array of spots obtained with a real human eye. Aberrations in the eye's optics cause displacements in the positions of the spots from which the wavefront error of the eye can be reconstructed.