The Chromatic Aberration of the Eye and its Importance in the Modern World

Abstract

The human eye has various aberrations that distort the image formed
on the retina. Monochromatic aberrations are the distortions present at
a single wavelength and chromatic aberrations are wavelength dependent. Longitudinal chromatic aberration (LCA) describes the difference in defocus at different wavelengths. The LCA of the human eye is approximately 2 dioptres (D) across the visible spectrum. Normally we are unaware of these distortions, however, they do play an important role in our vision. The aim of this thesis was to investigate the importance of these aberrations in the context of the modern world.

The illuminant spectra that we are exposed to today are quite different
from 100 years ago. Because LCA results in a difference in defocus with
wavelength this means that the amount of defocus blur in the retinal
image will change depending on the spectrum of light. In this thesis
findings are reported indicating that there are certain illuminant spectra
for which the chromatic fringes due to LCA were more visible. We
also investigated how people accommodated to spectra made up of two distinct narrowband LEDs. The findings suggest that people do not
accommodate optimally to these spectra.

There is also increasing interest in blurring stimuli realistically. This is
partly with the emergence of virtual reality, so that 3D scenes appear as realistic as possible, but also has more clinical applications in trialling the effects of different corrective lenses on vision before the lenses are made (or inserted in the case of intraocular lenses). We investigated the importance of including monochromatic aberrations when rendering out of focus stimuli. It seems that monochromatic aberrations do make the stimuli appear more realistic, however, they did not have a significant impact on visual acuity.