Monochromatic aberrations and point-spread functions of the human eye across the visual field.

Abstract

The monochromatic aberrations of the human eye along the temporal meridian are studied by a novel laser ray-tracing method. It consists of delivering a narrow laser pencil into the eye through a given point on the pupil and recording the aerial image of the retinal spot with a CCD camera. The relative displacement of this image is proportional to the geometrical aberration of the ray (laser pencil) at the retina. We scanned the pupils of four observers in steps of 1 mm (effective diameter, 6.7 mm) and for five field angles (0 degree, 5 degrees, 10 degrees, 20 degrees, and 40 degrees). In addition, the aerial image for each chief ray is a low-pass-filtered version of the retinal point-spread function corresponding to a fully dilated pupil. The resulting spot diagrams, displaying the distribution of ray aberrations, are highly correlated with these point-spread functions. We have estimated the wave-front error by fitting Zernike polynomials (up to the fifth order). Despite the large variation found among observers, the overall rms wave-front error is relatively homogeneous. At the fovea, the average rms value was 1.49 microns when the second-order terms (defocus and astigmatism) were considered; this was reduced to 0.45 micron when the second-order terms were ignored. The rms values increase slowly, in a roughly linear fashion with eccentricity, such that at 40 degrees they are approximately double. These results are consistent with previous findings on the off-axis optical quality of the eye.