Low_resolution_Thesis_CDD_221009_public - Visual Optics and ...

ANNEX A
A.3.1. Scheimpflug imaging topography
We collected repeated measurements of the anterior and posterior corneal surface of
three healthy eyes of three subjects with a Pentacam ® (Oculus, Wetzlar, Germany)
Scheimpflug-imaging topographer. This method provides quantitative elevation maps
of both surfaces, sampled in a uniform square grid of side 100 m (see Fig. A.1, left)
(Perez-Escudero et al., 2009b). The instrument’s software corrects the geometrical
distortion of both corneal surfaces (due to the tilt of optical surfaces which is a
characteristic of Scheimpflug cameras), and the optical distortion of the posterior
surface, (due to its imaging through the anterior corneal surface (Dubbelman and
Heijde, 2001)). We collected 33 measurements of the right eye of Subject 1 (age 26),
23 measurements of the right eye of Subject 2 (age 25), and 35 measurements of the
right eye of Subject 3 (age 37). All the measurements on each eye were taken
consecutively in one single session, which took 45 minutes or less.
In addition to these data, we used data from a previous study (Perez-Escudero et
al., 2009b), of 27 eyes of 14 patients before and after LASIK surgery, and 18 eyes of 9
control subjects. Each subject was measured in three or four experimental sessions on
different days (over the first month post-surgery in patients , and over one week for
controls), and the measurements were repeated between 3 and 6 times per
experimental session.
A.3.2. Corneal videokeratoscopy
We used an Atlas ® 990 (Carl Zeiss Meditec AG, Jena, Germany) topographer based
on Placido disks to collect repeated measurements of the anterior corneal surface of
eyes. We obtained 55 repeated measurements on Subject 1 and 20 measurements on
Subject 2. The subjects and eyes are the same that participated in the Scheimpflug
corneal topography measurements described above. Each session took less than two
hours. The videokeratoscope provides a 3D elevation map sampled in concentric
circles around the corneal apex (see Fig. A.1, center).
A.3.3. Lens profilometry
In-vivo corneal measurements are subject to variability in the sample, and also to
uncertainty in centration and alignment. We also used a microscopy-based non-contact
optical profilometer (PlSensofar, Barcelona, Spain) (Artigas et al., 2004) to
obtain repeated profilometric measurements of an aspheric intraocular lens. The
instrument was programmed to take 36 2-D profiles at identical exact conditions
(within less than 140 minutes), using the confocal mode of the instrument, as
described in Ref. (Dorronsoro et al., 2009). Each profile extends about 5.5 mm,
consisting of 1658 data points equispaced in the horizontal direction. Accuracy in the
vertical direction is within 0.1 m.
A.3.4. Simulations
We generated an ideal rotationally symmetric ellipsoid of radius R = 8 mm and
asphericity Q = 0.3. We used the same sampling as the one used by Pentacam (grid of
100 m squares). We added gaussian noise along the z direction at each point, with
10-m standard deviation. The procedure was repeated 1000 times.
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