Alfredo Dubra's PhD thesis - Imperial College London

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6. Tear topography dynamics experiment M = 0.134 N M = 0.193 N M = 0.254 N mk1/46 st3/15 (a) (b) (c) im4/17 M = 0.240 N M = 0.484 N M = 0.154 N pb2/92 mk1/33 kh3/47 (d) (e) (f) M = 0.412 N M = 0.489 N (g) te2/49 (h) te2/13 Figure 6.8: Normalized second order moment of the AC term of tear topography lateral shearing interferograms (M N ) illustrating some of the different tear topography features. 105
Chapter 7 Summary and discussion The design of a double shearing interferometer for evaluating the dynamics of the front surface of the pre-corneal tear film has been described. The instrument was built and tested on 20 subjects, and the data was analyzed with purpose-developed software. In order to achieve the topography integration from finite differences, we generalized an existing reconstruction method based on the DFT, which allows the processing of data volumes that can not be achieved with current computing powers and conventional pseudoinverse reconstruction techniques. The data processing software was tested in a set of recorded interferograms that illustrate the different features found on the tear topography, to become familiar with the limits of both the software algorithms and the theory on which these algorithms are based. We found that observing the back-reflection of the tear surface with normal coherent illumination might be a qualitative tool for studying the tear topography evolution, without the need for data processing and with relatively high resolution. The only problem that might prevent this technique from being used clinically is the small tolerance to eye misalignment. A modified version of Prydal’s experiment was performed to estimate the tear film thickness [83], with the purpose of estimating the amplitude of back-reflections from surfaces within the eye other than the front surface of the tear. It was found, based on fringe contrast estimation that the intensity of these reflections are around 150 times lower than those of the front surface of the tear, thus introducing very little 106
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A Shearing Interferometer for the E
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Acknowledgements Pursuing the PhD d
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Contents Contents 4 List of Figures
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CONTENTS 5.1 Prydal type experiment
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List of Figures 1.1 Young’s exper
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LIST OF FIGURES 5.2 Sequence of ref
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Chapter 1 Introduction Assessing an
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1. Introduction (a) (b) Figure 1.3:
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1. Introduction was then modified a
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1. Introduction been achieved by us
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1. Introduction A less significant
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1. Introduction It should also be m
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Chapter 2 Lateral shearing interfer
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2. Lateral shearing interferometer
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P P 2. Lateral shearing interferome
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3. Data processing If we look at th
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3. Data processing term on the retr
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3. Data processing mk1/33 (a) (b) k
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3. Data processing mk1/46 (a) (b) (
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3. Data processing 0.43 mk1/46 (a)
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3. Data processing 3.3 Pupil positi
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Page 67 and 68: Chapter 4 Wavefront reconstruction
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Page 79 and 80: Chapter 5 Preliminary experiments 5
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Page 113 and 114: A. Preliminary study of feasibility
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Page 127 and 128: Bibliography [1] T. Young. The Bake
Page 129 and 130: BIBLIOGRAPHY [22] P. Artal, S. Marc
Page 131 and 132: BIBLIOGRAPHY [44] Austin Roorda and
Page 133 and 134: BIBLIOGRAPHY [67] W.N. Charman and
Page 135 and 136: BIBLIOGRAPHY [89] J.P. Craig, P.A.
Page 137: BIBLIOGRAPHY [115] Frangois C. Delo
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Alfredo Dubra's PhD thesis - Imperial College London

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