Low_resolution_Thesis_CDD_221009_public - Visual Optics and ...

INTRODUCTION
1.1. MOTIVATION
The framework of this doctoral thesis is physiological optics and in particular the
optics of the cornea. The research reported here is dedicated to the study of refractive
corrections applied to the cornea, that aim at altering the shape of the first surface of
the eye, the most accessible and the most important from an optical point of view.
Specifically, this research work addresses refractive surgery and contact lenses. We
will study the physical phenomena involved in corneal ablation and in fitting lenses on
the cornea, and we will show results of the shape changes that they introduce, their
optical consequences and their visual impact.
Corneal ablation in refractive surgery and fitting of contact lens are well
established procedures for monofocal corrections. Multifocal corrections have also
been introduced in the clinical practice, both in the form of contact lenses and
refractive surgery. Customization and wavefront guided corrections, both for ablation
algorithms and lens designs are also a hot topic, not only in research laboratories but
also a major focus on ophthalmic industry and advanced clinical practice.
However, there are still many open questions and plenty of room for
improvement, both in monofocal, multifocal, optimized and customized refractive
corrections applied to the cornea. A better knowledge of the physical processes
(ablation and fitting), isolated in controlled conditions, will provide the understanding
and quantification needed to improve the corrections, and in particular the optical
quality (and ultimately, vision) of the treated eye. This thesis is based on the use of
physical models, artificial eyes, and measurements on patients, and advanced methods
for surface characterization and optical quality assessment to study in detail corneal
ablation and contact lens fitting. The results will be relevant for the improvement of
the techniques, procedures and/or designs associated to refractive corneal ablation and
contact lens fitting.
These two fields of study, refractive surgery and contact lenses, are
interconnected, not only as many of the methods that can be used for research are
similar, but also as mutual feedback can be gained from the results. Contact lenses are
a good laboratory test for evaluating and improving multifocal patterns and designs,
that are relevant in refractive surgery. Achieving a higher control on the ablation
process on curved surfaces will make possible the precise manufacture of customized
and/or wavefront optimized contact lenses by laser ablation. The fine control of the
final surface geometry requires deeper understanding on laser efficiency effects that
have affected refractive surgery outcomes in the past (and still does, although to a
minor extent).
Corneal abation and contact lens fitting aim at altering the first surface of the eye
to change its optical performance (in most cases to reduce ametropia or to induce
multifocality). However, as will be shown in this thesis, the posterior surface of the
cornea (or the contact lens) can also play a role. The posterior surface of the cornea,
and the instruments used for its biometry, will also be studied in this thesis in the
context of refractive surgery, through the use of another model cornea.
Physical and optical factors contribute to the quality of the retinal image, but they
constitute only the initial steps of the vision process. Neural factors need also to be
considered when determining visual quality following a refractive procedure or a
contact lens fitting. In this thesis, we will approach the study of these visual
implications with multifocal contact lenses by a through-focus visual acuity test. The
study was performed with contact lenses of different designs (including monofocal
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