Low_resolution_Thesis_CDD_221009_public - Visual Optics and ...

INTRODUCTION
6. Evaluation and understanding of optical performance of eyes with RGP contact
lenses.
7. Reasons for the improved optics with RGP contact lenses.
8. Evaluation of optical performance with monofocal and multifocal soft contact
lenses in physical and real eyes.
9. Understanding of the failure/success of multifocal contact lenses in producing
effective multifocality, on an individual basis.
10. Correlations of visual and optical quality in patient eyes.
1.14. THESIS SYNOPSIS
In this thesis we studied the physical implications of corneal ablation and the effect of
contact lens fitting. Both are complex phenomena, entangled with biological effects,
and with many mixed (and often yet unbounded) physical causes. Our approach was to
study the problem starting with a high degree of control, and lowered complexity. In
following steps, the degree of complexity is progressively increased.
Three experimental models have been developed during this thesis, with the aim
of isolating the physical process of interest from the inherent variability of human eyes
and gaining control (avoiding biomechanics, theoretical assumptions, crossinteractions,
tear effects, etc): 1) a model for the study of the laser ablation of the
anterior cornea, 2) a model for the study of the posterior surface of the cornea which
was applied to the study of posterior cornea stability after refractive surgery, and 3) an
in-vitro model of contact lens fitting, oriented to multifocal lenses. These three models
were used to study, with high precision, the optical changes produced by the
manipulation of the refractive properties of the cornea.
To support those experimental studies, we developed new measurement methods
and procedures. In particular, a new generation of LRT aberrometer was implemented
for this Thesis, and methodologies for the measurement of changes in optical surfaces.
These were applied to the experimental models. Besides, during this thesis different
clinical studies were performed on patients, of the specific questions studied in vitro:
the posterior surface of the cornea, and contact lens fitting (from monofocal RGP –
semirigid- contact lenses to soft multifocal contact lenses).
The body of this thesis is structured as follows:
Chapter 2 describes the common methods used throughout this thesis:
instruments for the precise measurement of optical surfaces (and real and artificial
corneas in particular), a versatile system (Laser Ray Tracing) for the measurement of
optical quality of the eye, methods for the measurement of optical performance, and
different techniques for computer simulation of different phenomena.
Chapter 3 introduces in vitro plastic artificial eye model for the study of the
physical factors involved in refractive surgery. Efficiency effects were measured by
ablating flat and spherical artificial corneas of PMMA, with a conventional refractive
surgery system, provided with non-optimized algorithms.
In Chapter 4 a study of the ablation process vs material, number of pulses and
fluence is presented, aiming at a better understanding the use of plastic models in
refractive surgery, and providing valuable information of the optical and ablation
properties of the materials and for the improvement ot the model. A new material,
Filofocon A, is introduced, with ablation properties that make it more suitable for
refractive surgery models.
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