Alfredo Dubra's PhD thesis - Imperial College London

1. Introduction
(a)
(b)
Figure 1.3: Gullstrand’s method for estimating the aberrations introduced by the
cornea. The method is a rudimentary corneal topography, consisting of imaging a set
of squares like the one in (a) after reflection from the first corneal surface and measuring
its deformation as shown in (b). This images were reproduced from Helmholtz’s
Handbuch der Physiologischen Optik [3].
One century later, Gullstrand [3] studied extensively the monochromatic aberrations
of the eye, the influence of the concavity of the tear in vision quality, the scattering
introduced by the fibres in the lens and the cornea and the lack of rotational symmetry
shown by the aberrations in the eye. In his work, Gullstrand tried to characterize the
aberrations of the eye in terms of the caustic, and studied the aberrations introduced
by the cornea by performing a very elementary corneal topography, consisting of
imaging a set of distorted squares on the front corneal surface and measuring their
deformation, as shown in figure 1.3.
1.1 Wavefront sensing in the human eye
We can think of wavefront sensing in the eye as the evaluation of the monochromatic
aberrations of the eye other than piston, tip and tilt, as these do not degrade the
imaging properties of the eye. We could also say that Young is the pioneer of pupilplane
wavefront sensing in the eye, while Gullstrand gave the first steps in image-plane
wavefront sensing in the human eye. However, we can consider that the modern era
of wavefront sensing in the eye did not start until 1961, with the work by Smirnov [4]
where a subjective experiment was set up to sample the wavefront slope across the
pupil and then to estimate the point spread function (PSF) of the eye. Smirnov also
suggested the tear film as a possible source for the noticeable inter-subject variability
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