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 1.9. CONTACT LENSES Refractive surgery and contact lenses can be considered alternative approaches to achieve the same goal: the refractive correction of the eye by manipulating the corneal power. While the former achieves this goal by permanently removing tissue, the latter places a thin lens of transparent material on the cornea, which is removable. The tissue removed in refractive surgery is sometimes conceptually modelled as a contact lens removed from the cornea (Munnerlyn et al., 1988). Understanding the optical coupling between the contact lens and the optics of the eye is not easy, as we will discuss in the following sections. The problem is more complicated that combining the intended design of the lens and the aberrations of the eye, as one needs to consider the fitting of the lens: tear film on the lens, tear lens between the contact lens and the cornea, lens position, lens material, hydration, conformity and flexure. All these factors, and many others, affect the final optical performance. At the initial stages of this thesis there were very few studies on contact lens fitting in terms of optical aberrations, but with suggestive results. 1.9.1. The origins of contact lenses Leonardo da Vinci in 1508, René Descartes in 1636, and Thomas Young in 1801, anticipated the idea of contact lenses (Phillips and Speedwell, 1997), but the first one to suggest their use to correct the refractive errors of the eye was Sir John Herschel, in 1845 (Walls, 1950), who never tested these ideas. Interestingly, Herschel pointed out that the operation of “applying in contact with the surface of the eye some transparent animal jelly contained in a spherical capsule of glass” (fitting a contact lens) “…would, of course, be delicate, but certainly less so than that of cutting open a living eye, and taking out its contents”. This sentence, that is recognized to constitute the beginning of modern thinking in contact lenses, also seems to anticipate the basic idea or refractive surgery as an alternative procedure for correcting the refractive errors of the eye, although (even more) invasive than contact lenses (See page 185 of this thesis for a detailed revisit of that moment (Walls, 1950)). It was not until 1887 that a German glassblower, F.E. Muller, produced the first eye covering to be seen through and tolerated. In 1888, the German physiologist Adolf Eugen Fick constructed and fitted the first successful contact lens. He fabricated and fitted the glass lenses, initially on rabbits, then on himself, and lastly on a small group of volunteers (Phillips and Speedwell, 1997). Plastic (PMMA) was not introduced until 1936 by Feinbloom. By the end of the 1970s, and through the 1980s and 1990s, a range of oxygen-permeable but rigid materials were developed. The first soft (hydrogel) lenses appeared in the late 1960s. These lenses were soon prescribed more often than rigid lenses, mainly due to their immediate comfort. 1.9.2. Optical differences between contact lenses and spectacles Similarly to what happens in refractive surgery, correcting refractive errors with contact lenses is different in optical terms to correcting with spectacles. The more apparent effect is cosmetic. The magnification of the eyes is eliminated (an observer sees the eyes looking their normal size), and reflections are also removed. Unlike with spectacle lenses which limit the field of view both by the spectacle frame (and the area covered by the lens) and magnification and prismatic effects, with 52
INTRODUCTION contact lenses the field of view remains unchanged, as the lens moves with the eye.. As for binocular vision, prismatic and magnification effects can produce alterations in convergence with spectacle corrections, specially for anisometropic wearers, that are not present with contact lenses. Field distortions, curvatures and oblique aberrations associated to gaze through the periphery of spectacle lenses are not present in contact lenses neither. On the other hand, halos and scattering (from lens deposits, interruptions to the tear of abrupt transitions between zones of the lens) are more common in contact lenses. 1.9.3. Rigid gas permeable (RGP) contact lenses It is widely accepted in the clinical practice that RGP contact lenses (made of oxygenpermeable polymers) provide the best ophthalmic correction, at least from a purely optical viewpoint (Phillips and Speedwell, 1997). RGP contact lenses are expected to mask the anterior corneal surface with a perfectly regular surface, and fill in with tear all the corneal irregularities. The refractive index similarity between the tear film and the anterior corneal surface reduces the impact of corneal aberrations (Griffiths et al., 1998). The better visual response of RGP contact lenses, compared to soft contact lenses (which would produce the same magnification) or spectacles, is well documented in the optometry literature (Griffiths et al., 1998, Phillips and Speedwell, 1997). Most of these studies are based on psychophysical measurements of visual performance and conclude that RGP contact lenses provide higher visual acuity and contrast sensitivity. RGP lenses on-eye are affected by a number of forces. The correct fitting needs a balance among those forces: capillary attraction between the lens and the cornea, gravity, tear meniscus, lid forces, and frictions. The back optics zone radius (BOZR) is the main parameter to vary, when looking for an optimal fitting balance. A correctly fitted contact lens has certain movement during and after blinking, but rests in a stable position between blinks. A particular type of RGP lenses are reversed-geometry contact lenses. These lenses have a secondary curve in the periphery that is steeper than the base curve. These lenses are used in two particular cases: 1) to fit the topographically altered post surgical corneas, and 2) Ortho-K procedures: flattening the cornea after extended wear, to correct refractive errors without surgery. 1.9.4. Soft contact lenses While rigid lenses require a period of adaptation before full comfort is achieved, the main advantage of soft lenses is that they are immediately comfortable. They allow longer wearing times, and do not produce corneal oedema or corneal deformations, or at least to a less extent. Soft contact lenses remain typically more centered on the cornea, and the movements with blinking are small, if compared with RGP lenses. These lenses are almost unaffected by gravity. However, optical quality (Torrents et al., 1997) and visual outcomes are more variable and often not as good as those obtained with rigid lenses. The tear film is not so stable, and the lens shape can fluctuate with blinking. The materials of the lenses are softer than the cornea, and so are more readily deformed by eyelid pressure. The refractive result is neither fixed not absolute. It can change from moment to moment, from day to day. 53
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 and 50: INTRODUCTION corneal surface may be
Page 51: INTRODUCTION Algorithm design: The
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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