Low_resolution_Thesis_CDD_221009_public - Visual Optics and ...

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$XXX Congress of the European Society of Cataract and Refractive ...$

CHAPTER 1 evolution of the process. These models pretend to obtain precise prediction of the outcomes of the surgery, by including a detailed description of the phenomena involved. Kwon and Bott have recently presented a model that takes into account the corneal remodelling that occurs through healing (Kwon and Bott, 2008). All these numerical models need experimental data for validation and parameter adjustment that are presumably difficult to obtain from measurements on real corneas. 1.7.6. Experimental models for refractive surgery Ablation of plastic flat surfaces had been used before in the context of refractive surgery (Gottsch et al., 1996, Odonnell et al., 1996, Roszkowska et al., 2003), to assess post-operative roughness. Corneal laser ablation models have not only attracted the interest of the scientific community, but also of normalization agencies. For instance, the ANSI Z80.11-2007 norm requires the ablation of plastic plates for calibration (energy adjustment and laser profile testing) of corneal refractive surgery (2007). The standard also recommends the use of plastic corneal models for in vitro testing of the ablation characteristics of the laser systems and to validate experimentally mathematical models, simulations, and ablation algorithms. The Ophthalmic Devices Panel of the Food and Drug Administration (FDA) is currently evaluating the ANSI Z80.11 Standard for recognition (2008), and the FDA section on Medical Devices has pointed out the necessity to develop accurate calibration techniques to assure that the achieved corneal ablation depth map equals the one intended through plastic corneal models (Drum, 2007, Drum, 2003, Drum, 2005). 1.8. OPEN QUESTIONS IN CORNEAL REFRACTIVE SURGERY Refractive outcomes are subject to some variability due to regression (Chayet et al., 1996), hydration (Feltham and Stapleton, 2002) or other factors that lead to empirical adjustments of the ablation nomogram (Mrochen et al., 2006, Ditzen et al., 1999). Concerning wavefront-guided refractive surgery, there is still an important lack of predictability (Kohnen et al., 2007). Despite some initial promising clinical results and some evidence that the increase of spherical aberration is attenuated (Mrochen et al., 2000) in many cases spherical aberration is still introduced. Although some studies show trends toward better visual and optical outcomes following wavefrontcustomized procedures (Kim and Chuck, 2008), the improvement is hardly significant when compared with the new generation of conventional procedures (Padmanabhan et al., 2008, Netto et al., 2006, Alio and Montes-Mico, 2006). Many causes have been pointed out for the relatively minor impact of aberration correction (Kohnen et al., 2007), such as fluctuations in the aberrations or errors in their measurement, centration, alignment or torsion errors (during the measurements or the ablation), and flap creation effects. Corneal biomechanics is another potential cause for the inaccurate prediction of the corneal postoperative shape. Therefore, the current objective of refractive surgery is still preventing the induction of spherical aberration and the changes in asphericity. This objective is required for successful wavefrontguided surgery. The controlled induction of shape changes required in customized ablation algorithms, entails 1) an adequate profile design (Manns et al., 2002a, Klein, 1998, Mrochen et al., 2004), 2) the correct transfer of the pattern to the cornea through deep knowledge of the ablation process, 3) validated numerical models based on experimental data, 4) the consideration of biological effects and 5) the back surface of the cornea, as described hereafter: 50
INTRODUCTION Algorithm design: The design of the ablation pattern is the key element for improving refractive surgery. The patterns, and the algorithms used to apply them to the cornea, are proprietary. Although much of research assumes certain shape (Munnerlyn or parabolic approximations) the programmed pattern could deviate from these equations. Furthermore, even calculations and simulations of the manufacturers based on their own nominal proprietary algorithms can be incorrect, as the effective ablation pattern can be substantially different of that pretended, due to optical, mechanical or electrical variability or miss-calibrations. Tools for precise assessment of the ablation pattern, both in flat and in curved surfaces, are an important requirement for the improvement of refractive surgery. These can allow the direct comparison across laser systems, and help explain clinical results. Transfer of the ablation pattern to the cornea: Undoubtedly, not only the ablation pattern design itself, but also how accurately it is transferred to the cornea (i.e. physical aspects of the ablation process) determine the optical outcomes of the surgery. Experimental studies of the physics of the ablation in curved surfaces, isolated from biological processes, performed in controlled environments with low variability (from ocular parameters, centration or alignment), can help understand and improve the energy transfer to the cornea. Precise tools and procedures for measuring the outcomes of the ablation (from isolated pulses to complete patterns) are also essential. Input data and experimental validation for numerical models: Computational models for the precise simulation of corneal ablation require several input numerical parameters (mainly physical properties of the material and physical parameters of the laser). Many of them need to be measured and checked experimentally. Moreover, the whole model needs validation, by testing it over different controlled conditions. Calibration procedures for the lasers, and measurements of their efficiency effects, are among the most needed results in this field. The role of Biological effects: Most models of the effect of wound healing and biomechanical changes on refractive surgery are vague and mostly at a quantitative stage. Although these effects are likely to produce uncertainty and instability, the boundaries of biological effects are not yet defined, as they are entangled with purely physical effects. More studies on long term and short term shape surface shape changes after surgery are needed. The role of the back surface of the cornea: The biological changes (wound healing or biomechanical effects) will likely affect the back surface of the cornea, which can compensate in part the aberrations of the anterior surface. Several studies have shown important changes in the posterior corneal surface suggesting an influence of corneal biomechanical effects in the optical outcomes, although these results are controversial. 51
Page 1: Doctoral thesis Corneal Ablation an
Page 5 and 6: Contents Corneal Ablation and Conta
Page 7 and 8: 2.2.1. Fitting surfaces............
Page 9 and 10: 5.3.3. Ablation efficiency factors
Page 11: 10.5. DISCUSSION...................
Page 14 and 15: We thank José Antonio Sánchez-Gil
Page 16 and 17: BOZR Back Optic Zone Radius BCVA Be
Page 19 and 20: INTRODUCTION 1.1. MOTIVATION The fr
Page 21 and 22: INTRODUCTION 1.2. THE OPTICAL SYSTE
Page 23 and 24: INTRODUCTION Myopia is a very commo
Page 25 and 26: INTRODUCTION a point focus: the dif
Page 27 and 28: INTRODUCTION system, and tilt repre
Page 29 and 30: INTRODUCTION term Z 0 2 stands for
Page 31 and 32: INTRODUCTION which image was shadow
Page 33 and 34: INTRODUCTION The defocus Zernike te
Page 35 and 36: INTRODUCTION 1.4.6.3. Internal Aber
Page 37 and 38: INTRODUCTION 1.5.2.3. Alternating v
Page 39 and 40: INTRODUCTION and further-more, at l
Page 41 and 42: INTRODUCTION alcohol is used to loo
Page 43 and 44: INTRODUCTION changes in reflectivit
Page 45 and 46: INTRODUCTION Marcos et al. (Marcos
Page 47 and 48: INTRODUCTION 1.7.3. Ablation effici
Page 49: INTRODUCTION corneal surface may be
Page 53 and 54: INTRODUCTION contact lenses the fie
Page 55 and 56: INTRODUCTION 1.10.1. Tear studies A
Page 57 and 58: INTRODUCTION there are still many u
Page 59 and 60: INTRODUCTION 6. Evaluation and unde
Page 61 and 62: METHODS 2Chapter Chapter 2 - Method
Page 63 and 64: METHODS 2.1. MEASUREMENT OF OPTICAL
Page 65 and 66: METHODS In both profilometers, cust
Page 67 and 68: METHODS The measurement method that
Page 69 and 70: METHODS Fig. 2. 9. Set of points in
Page 71 and 72: METHODS Slit lamp Scheimpflug Camer
Page 73 and 74: METHODS representing the deviation
Page 75 and 76: METHODS 2.2.2.2. Ablation pattern f
Page 77 and 78: METHODS direction. These calculatio
Page 79 and 80: METHODS eye through the whole pupil
Page 81 and 82: METHODS (1993) power thresholds for
Page 83 and 84: METHODS alignment (frontal-illumina
Page 85 and 86: METHODS Fig. 2. 24. Example frame f
Page 87 and 88: METHODS 4) New image processing too
Page 89 and 90: METHODS Fig. 2. 28. Corrected entra
Page 91 and 92: METHODS Badal lens, corresponds to
Page 93: METHODS Each VA measurement consist
Page 99: REFRACTIVE SURGERY PMMA MODEL 3.1.
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CHAPTER 3 optimization of refractiv
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CHAPTER 3 These data demonstrate th
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CHAPTER 3 regression line, since it
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CHAPTER 3 Figure 3.3 shows one of t
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CHAPTER 3 Ablation efficiency facto
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CHAPTER 3 considering the same set
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CHAPTER 3 3.5.3 Impact of correctio
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ABLATION PROPERTIES OF FILOFOCON A
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OPTIMIZED LASER PLATFORMS 5.1 ABSTR
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CHAPTER 5 pulses. Fluence, repetiti
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CHAPTER 5 ablations. The slit-confo
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CHAPTER 5 (Anera et al., 2003): d S
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CHAPTER 5 asymmetries also appeared
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CHAPTER 5 5.3.4. Ablation patterns
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CHAPTER 5 a) b) : 6.5 mm c) Fig. 5.
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CHAPTER 5 achieve proper reflection
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CHAPTER 5 Both the ablation algorit
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HYBRID PORCINE/PLASTIC MODEL 6.1. A
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CHAPTER 6 6.3.1. Hybrid porcine-pla
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CHAPTER 6 is detected. Therefore, i
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CHAPTER 6 no preferential orientati
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ANTERIOR AND POSTERIOR CORNEAL ELEV
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183
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SOFT CONTACT LENS FITTING USING MOD
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SOFT CONTACT LENS FITTING USING MOD
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ON-EYE OPTICAL PERFORMANCE OF RIGID
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SOFT MONOFOCAL AND MULTIFOCAL CONTA
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SOFT MONOFOCAL AND MULTIFOCAL CONTA
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CORRELATION BETWEEN RADIUS AND ASPH
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CONCLUSIONS Conclusions This thesis
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CONCLUSIONS 5We have developed a pr
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CONCLUSIONS LIST OF METHODOLOGICAL
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CONCLUSIONS FUTURE RESEARCH LINES T
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CONCLUSIONS LIST OF PUBLICATIONS AN
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REFERENCES References AIZAWA, D., S
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REFERENCES PHOTODECOMPOSITION (APD)
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REFERENCES DORRONSORO, C., CANO, D.
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REFERENCES GISPETS, J., ARJONA, M.
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REFERENCES KOPF, M., YI, F., ISKAND
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REFERENCES MARCOS, S., DORRONSORO,
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REFERENCES NOVO, A., PAVLOPOULOS, G
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REFERENCES SAKIMOTO, T., ROSENBLATT
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REFERENCES WANG, L., DAI, E., KOCH,
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RESÚMENES pacientes reales fue com
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RESÚMENES experimentales de cirug
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RESÚMENES cada punto de las cornea
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RESÚMENES plástico medidas anteri
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RESÚMENES 8 Evaluación óptica de
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RESÚMENES 9 Prestaciones ópticas
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RESÚMENES 10 Calidad óptica y cal
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RESÚMENES A Correlación entre rad
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CONCLUSIONES clínicos. La descripc
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CONCLUSIONES 12 Las superficies ocu
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CONCLUSIONES IMPLICACIONES DE ESTA
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CONCLUSIONES contribuyen a la compr
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(y muchísimo más difícil). Me da
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