Rozprawy doktorskie na temat „Correction de refraction”

L'ostéoporose est une maladie caractérisée par une réduction de la masse osseuse et une augmentation de la porosité. Elle affaiblit les os et peut conduire à des fractures de fragilité. Globalement, 1/3 des femmes de plus de 50 ans et 1/5 des hommes de plus de 50 ans subiront des fractures liées à l'ostéoporose, contribuant à plus de 8,9 millions de fractures annuelles dans le monde. Ces fractures peuvent être prévenues si elles sont détectées et traitées suffisamment tôt. Plusieurs techniques ont été développées pour évaluer la qualité osseuse, l'échographie émergeant comme une option peu coûteuse, portable et sûre. L'imagerie par ultrasons du cortex des os longs permet l'évaluation de la qualité osseuse en estimant l'épaisseur corticale et la vitesse d'onde ultrasonore, des biomarqueurs de la résistance mécanique et du risque de fracture. Cependant, des défis se posent avec l'augmentation de la porosité corticale dans l'os ostéoporotique, rendant difficile la détection de la surface interne (endosteum) et limitant la qualité de l'image. L'objectif de ce travail est de concevoir une technique de reconstruction d'images capable d'améliorer les images échographiques de l'os cortical. Cela passe par la compréhension des facteurs influençant la qualité de l'image. Pour ce faire, des ensembles de données échographiques synthétiques et expérimentaux ont été générés. Nos résultats démontrent l'estimation réussie de l'épaisseur corticale et de la vitesse d'onde ultrasonore en utilisant l'imagerie par ultrasons pour un os cortical homogène. L'estimation in vivo de la vitesse d'onde au cortex tibial de sujets sains a atteint une précision de moins de 3%. Cependant, pour les os dégradés, une porosité corticale accrue et une taille de pore vasculaire plus grande créent un bruit qui obscurcit la visibilité de l'interface endostéale. Un nouvel algorithme de formation de faisceau spéculaire corrigé de la réfraction a été proposé pour améliorer la visibilité de l'interface endostéale. L'application de cet algorithme à la fois à des ensembles de données ex vivo et in vivo a révélé une visibilité améliorée par rapport à la formation de faisceau Delay-and-Sum (DAS) traditionnelle. Ce travail offre une meilleure compréhension des facteurs affectant le contraste des images échographiques osseuses et propose de considérer les diffuseurs comme des réflecteurs spéculaires pour améliorer la visibilité de l'interface endostéale. En évaluant la spécularité de l'interface endostéale, il devient possible d'évaluer potentiellement la rugosité de l'endosteum. Cela ouvre la voie à la conception de nouveaux quantificateurs de qualité mécanique osseuse. L'imagerie échographique osseuse montre des promesses dans l'identification et le suivi des personnes présentant une faible qualité mécanique osseuse corticale à risque de fracture ostéoporotique
Osteoporosis is a disease characterized by a decrease in bone mass and an increase in porosity, weakening the bones and potentially leading to fragility fractures. Globally, one-third of women over the age of 50 and one-fifth of men aged over 50 will experience osteoporosis-related fractures, contributing to over 8.9 million fractures annually worldwide. Early detection and treatment can prevent these fractures. Several techniques have been developed to assess bone quality, with ultrasound emerging as a cost-effective, portable, and safe option. Ultrasound imaging of the cortex of long bones allows for the evaluation of bone quality by estimating cortical thickness and ultrasonic wave-speed, which are biomarkers of mechanical strength and fracture risk. However, challenges arise with increased cortical porosity in osteoporotic bone, making it difficult to detect the inner surface (endosteum) and limiting image quality. The aim of this study is to design an image reconstruction technique to enhance ultrasound images of cortical bone. This involves understanding the factors influencing image quality. Synthetic and experimental ultrasound datasets were generated to achieve this. The results demonstrate successful estimation of cortical thickness and ultrasonic wave-speed using ultrasound imaging for homogeneous cortical bone. In vivo estimation of wave-speed at the tibial cortex of healthy individuals achieved a precision of less than 3%. However, for degraded bones, increased cortical porosity and vascular pore size create speckle that obscures the visibility of the endosteal interface. A novel refraction-corrected specular beamforming algorithm was proposed to improve the visibility of the endosteal interface. Application of this algorithm to both ex vivo and in vivo datasets revealed enhanced visibility compared to traditional Delay-and-Sum (DAS) beamforming. This study provides a better understanding of factors affecting bone ultrasound image contrast and proposes considering scatterers as specular reflectors to enhance endosteal interface visibility. By evaluating the specularity of the endosteal interface, it becomes possible to potentially assess the roughness of the endosteum. This opens a way for designing new bone mechanical quality quantifiers. Bone ultrasound imaging shows promise in identifying and monitoring individuals with low cortical bone mechanical quality at risk of osteoporotic fracture

Les considérations environnementales occupent une place croissante dans l'opinion publique ainsi que dans les politiques nationales et internationales. Le cas de la rivière en est un exemple particulièrement frappant : au centre d'enjeux multiples et pour certains hautement stratégiques (énergie, irrigation), elle est le théâtre d'un conflit d'usages donnant lieu à l'établissement de compromis particulièrement fins pour la gestion de la ressource. Dans les approches les plus courantes, la description de l'état et du fonctionnement d'un hydrosystème tel que celui de la rivière est effectuée par la mesure de variables physiques ou la mise en relation des variables d'intérêt avec les paramètres physiques quantifiables caractérisant le milieu (modèles hydrauliques, modèles hydrobiologiques). L'objectif de ce travail est donc de proposer une réponse à la question de la mesure de la géométrie de la rivière par télédétection. On s'attache tout d'abord à décrire le contexte particulier de la rivière mentionné plus haut puis à effectuer un état de l'art faisant ressortir une lacune pour la restitution du relief immergé par stéréo à travers l'eau avec des moyens légers. On propose ensuite une méthode complète d'acquisition d'images et de traitements permettant d'estimer le relief immergé de rivière. Le travail effectué repose sur la mise en oeuvre de moyens technologiques légers permettant une grande flexibilité pour l'acquisition des données. On se base sur les méthodes de stéréorestitution du relief, pour lesquelles on propose une adaptation au contexte spécifique de la photogrammétrie à travers l'eau. Enfin, on met en place des méthodes de correction des mesures brutes intégrant des contraintes a priori (cohérence hydraulique ; cohérence spatiale) pour la correction de l'effet de réfraction. L'application de la méthode développée en conditions opérationnelles sur une rivière peu profonde à fond de galets montre que la mesure du relief immergé par stéréophotogrammétrie est possible, et permet une représentation de la topographie du lit d'une qualité compatible avec les modèles hydrobiologiques (modèles habitat-poisson). On a ainsi développé, testé, validé et determiné les conditions d'application d'une méthode de mesure de la géométrie de la rivière par télédétection originale et complémentaire des technologies existantes.

The core function of optometrists is the prescribing of spectacles in order to alleviate symptoms and improve visual function. Most commonly, the spectacles are used to correct refractive errors and, less frequently, they are also used to correct a decompensated heterophoria. Whilst identifying and diagnosing a marked refractive error or decompensated heterophoria is relatively straightforward, the management of marginal or borderline cases is much more difficult, for there is no clear cut-off point between normality and abnormality. The literature search in this thesis reveals a lack of evidence-based research on the criteria for determining when a refractive or prismatic correction is required. The aim of the present research was to investigate at what point optometrists currently decide to prescribe spectacles in borderline cases, and to see if current prescribing habits relate to the advice given in the literature. Further aims were to investigate whether the correction of borderline refractive errors and decompensated heterophoria improves reading performance, and to investigate any association between an improvement in reading performance and symptoms. A practitioner survey was given to practitioners attending CET events during 2001 and to the UK Optometry E-mail discussion list. A wide variety of prescribing criteria were reported from the 37 respondents, and the presence of symptoms greatly influenced the decision to prescribe. Practitioners reported that their likelihood of prescribing when symptoms are present exceeded 50% for: horizontal aligning prism of ≥ 1.5Δ, vertical aligning prism ≥ 1.0Δ, hypermetropia of ≥ +0.75, reading additions of ≥ +0.75DS and astigmatism of ≥ -0.75DC. For asymptomatic patients, practitioners’ likelihood of prescribing exceeded 50% for: reading additions of ≥+1.50DS and astigmatic corrections of ≥-1.50DC. In the absence of symptoms, optometrists would not regularly correct any degree of hypermetropia or aligning prism up to the limits of the survey. In a prospective clinical trial, 58 subjects with decompensated heterophoria and 208 subjects with borderline refractive errors had their reading performance assessed with the Wilkins Rate of Reading Test both with the refractive or prismatic lens in place and with a placebo control lens using a double-masked randomised design. Analysis of the data indicated that prescribing prism for decompensated exophoria of 2Δ, a reading addition of +1.00DS and correcting oblique cylindrical errors is likely to result in an improvement in reading performance. Correlations between symptoms and the change in reading performance with small refractive or prismatic corrections were very weak. It is concluded that the correction of borderline decompensated heterophoria and refractive errors can improve rate of reading. Guidelines are suggested for the correction of these anomalies that are based on the present data on visual performance, as well as the literature on the effect of these anomalies on symptoms.

INTRODUÇÃO: A falta da correção óptica recentemente foi reconhecida como importante causa de baixa visão e parece ser um problema fácil de ser resolvido com o uso de óculos. No entanto, a falta da correção óptica é um problema complexo do seu diagnóstico ao tratamento, envolvendo a procura e alcance da assistência médica, além da confecção e uso dos óculos. OBJETIVOS: Determinar a frequência da necessidade de correção óptica em escolares; determinar a influência do absenteísmo no estudo da frequência da necessidade de correção óptica e suas causas; determinar o impacto da reconvocação dos faltosos na cobertura do atendimento oftalmológico; verificar cobertura oftalmológica prévia; verificar uso da correção óptica prescrita e causas de abandono de óculos. MÉTODO: Foi realizado um estudo transversal analítico. Escolares de 7 a 10 anos do ensino público de Guarulhos foram triados e encaminhados para exame oftalmológico na Campanha Olho no Olho 2006 e 2007. RESULTADOS: Foram triados 40.197 escolares e encaminhados 11.741 escolares com suspeita de problemas visuais. O absenteísmo na primeira convocação foi 42.5% e na reconvocação foi 62.2%. A Campanha alcançou 73.6% dos escolares encaminhados. A reconvocação ampliou a cobertura do projeto em 16.1%. A falta de orientação (não ter recebido aviso ou guia de encaminhamento) foi a razão mais frequente (35.6%) alegada para o não comparecimento, seguida de trabalho (20.6%) e doença (12.4%). A necessidade de óculos não foi fator associado ao comparecimento. Para 60.2% dos escolares foi a primeira oportunidade de exame ocular, sendo que 27.3% procuraram mas não tiveram acesso a consulta médica. Dos 1.379 escolares que já haviam feito exame, 48.3% utilizaram o SUS e 1.029 receberam prescrição de óculos em exame prévio. Destes, 899 (87.4%) fizeram os óculos e apenas 590 (57.3%) usavam os óculos no dia do exame. Dos óculos doados na Campanha, 84.7% dos escolares utilizavam a correção óptica após um ano. A estimativa da frequência da necessidade de correção óptica, na população estudada, foi de 6.9%. CONCLUSÕES: O erro refracional não corrigido foi a maior causa de baixa acuidade visual entre os escolares. A Campanha foi a primeira oportunidade de exame ocular para a maioria dos escolares. Existe uma parcela de pais que não leva seus filhos para exame, mesmo com oferecimento de facilidades (acesso, transporte, alimentação, duas oportunidades diferentes de exame gratuito realizado em fins de semana e doação de óculos). O absenteísmo poderia ser evitado em 87,1% dos casos, com melhor estruturação da primeira convocação. A reconvocação não é recomendada quando os recursos financeiros são escassos
INTRODUCTION: The lack of optical correction was recently recognized as an important cause of low vision and it seems to be an easy problem to be solved with the use of spectacles. However, it is a complex problem from its diagnosis to treatment, which includes medical assistance searching and finding, and spectacles acquisition and use. PURPOSES: To determine the frequency of optical correction need; to determine the impact of the recall of those absent in the ophthalmologic service coverage and its causes; to check the previous ophthalmologic coverage; to check the use of the prescribed optical correction and causes to neglect the use of spectacles. METHOD: An analytical cross-sectional study was conducted. Students between 7 and 10 years old of public education from Guarulhos were screened and referred to ophthalmologic exam in the Eye to Eye Campaign 2006 and 2007. RESULTS: 40.197 students were screened and 11.741 (29,2%) were referred with suspicion of visual problems. The absenteeism in the first call was 42.5% and in the recall 62.2%. The Campaign reached 73.6% of the referred students. The recall expanded the project coverage in 16.1%. The lack of guidelines (parents did not receive notification or referral guide) was the most frequent reason (35.6%) provided by parents for the non attendance, followed by work (20.6%) and disease (12.4%). The need of glasses was not related to the attendance. For 60.2% of the students, it was the first opportunity for ophthalmological exam, whereby 27.3% searched but did not have access to a medical visit. Among the 1.379 students who had already performed an exam, 48.3% used the Public Health System and 1.029 received prescription of glasses in the previous exam. From those, 899 (87.4%) made their glasses and only 590 (57.3%) were wearing glasses on the day of the exam. From the donated spectacles in the Campaign, 84.7% of the students were using the donated optical correction after one year. The estimate of optical correction need within the studied population was 6.9%. CONCLUSIONS: The uncorrected refractive error was the main cause of low visual acuity among students. The Campaign was the first opportunity of ocular exam for most of them. A significant number of parents did not take their children for ophthalmological exams, even when facilities (access, free transportation, meal, two different opportunities of free exam over the weekend and spectacle donation) were offered. For 87.1% of the absenteeism cases, the difficulties could have been overcome via improved structuring of the first call. A recall is not recommended when financial resources are low

Dizziness is a common, multifactorial problem that causes reductions in quality of life and is a major risk factor for falls, but the role of vision is a very under-researched area. This study aimed to investigate any link between dizziness and vision and to establish if changes in spectacle lens correction could elicit dizziness symptoms. A link between dizziness and self-reported poor vision was indicated in the epidemiological literature as shown by a systematic review, provided lightheadedness was not included in the definition of dizziness. Cases of individuals who reported vision-related dizziness were investigated to determine potential areas of research for this thesis and subsequently two studies investigated the effects of refractive correction changes on dizziness status. The first study was limited by logistical problems, although it highlighted limitations in the short form of the Dizziness Handicap Inventory that was used to quantify dizziness. Results of an optometry practice recheck study found that oblique cylindrical changes were significantly more likely to be associated with dizziness symptoms than other spectacle lens changes. It also highlighted that optometrists do not ask/record about dizziness symptoms with only 4% of records including “dizziness” as a problem when 38% of patients reported dizziness symptoms when directly asked. All studies highlighted a need for a patient-reported outcome measure to be designed to assess vision-related dizziness. Literature review, interviews with experts and patients and focus groups led to the development of a pilot questionnaire and subsequently a 25-item Vision-Related Dizziness instrument, the VRD-25. This was validated using responses from 223 respondents, with 79 participants completing the questionnaire a second time to provide test-retest data. Two subscales of VRD-12-frequency (VRD-12f) and VRD-13-severity (VRD-13s) were shown to be unidimensional and had good psychometric properties, convergent validity and test-retest repeatability. The VRD-25 is the only patient-reported outcome measure developed to date to assess vision related dizziness and will hopefully provide the platform to further grow this under-researched area that seems likely to provide important clinical information.
College of Optometrists sponsored the research with a Postgraduate Research Scholarship

For more than a century it has been known that the eye is not a perfect optical system, but rather a system that suffers from aberrations beyond conventional prescriptive descriptions of defocus and astigmatism. Whereas traditional refraction attempts to describe the error of the eye with only two parameters, namely sphere and cylinder, measurements of wavefront aberrations depict the optical error with many more parameters. What remains questionable is the impact these additional parameters have on visual function. Some authors have argued that higher-order aberrations have a considerable effect on visual function and in certain cases this effect is significant enough to induce amblyopia. This has been referred to as ‘higher-order aberration-associated amblyopia’. In such cases, correction of higher-order aberrations would not restore visual function. Others have reported that patients with binocular asymmetric aberrations display an associated unilateral decrease in visual acuity and, if the decline in acuity results from the aberrations alone, such subjects may have been erroneously diagnosed as amblyopes. In these cases, correction of higher-order aberrations would restore visual function. This refractive entity has been termed ‘aberropia’. In order to investigate these hypotheses, the distribution of higher-order aberrations in strabismic, anisometropic and idiopathic amblyopes, and in a group of visual normals, was analysed both before and after wavefront-guided laser refractive correction. The results show: (i) there is no significant asymmetry in higher-order aberrations between amblyopic and fixing eyes prior to laser refractive treatment; (ii) the mean magnitude of higher-order aberrations is similar within the amblyopic and visually normal populations; (iii) a significant improvement in visual acuity can be realised for adult amblyopic patients utilising wavefront-guided laser refractive surgery and a modest increase in contrast sensitivity was observed for the amblyopic eye of anisometropes following treatment (iv) an overall trend towards increased higher-order aberrations following wavefront-guided laser refractive treatment was observed for both visually normal and amblyopic eyes. In conclusion, while the data do not provide any direct evidence for the concepts of either ‘aberropia’ or ‘higher-order aberration-associated amblyopia’, it is clear that gains in visual acuity and contrast sensitivity may be realised following laser refractive treatment of the amblyopic adult eye. Possible mechanisms by which these gains are realised are discussed.

This work aims to improve the understanding of the fundamental characteristics of environmental flows by interpreting the turbulence in a 3D measurement domain. This thesis primarily describes the Tomographic PIV technique and the results of three experimental investigations of environmental flows. Two experiments were conducted in an open channel flow, divided into four sequential, identical pools, by a combination of regular grids. The first set of TPIV measurements were in the water column, while the second set of measurements were made along the channel bottom. The instantaneous structures in the flow were visualised and the turbulent kinetic energy k, energy dissipation ε and vorticity ω were analysed; their decay along the streamwise direction was revealed. Ejections (Q2) and sweeps (Q4) were identified along the channel bottom. A major contribution that resulted from the investigation pertains to the vibration correction of the cameras. TPIV measurements were taken of a regime of turbulent, forced fountain flows. The fountains were created by injecting a salt-water solution through a circular opening into the bottom of a reservoir of a water-ethanol solution, with their refractive indices carefully matched. The evolution of the fountain in its initial stages was captured and described in a series of chronological measurement volumes. Measurements of the fully developed fountains captured the large scale structures and their characteristics were analysed by considering the topology of the invariants of the velocity gradient tensor. The TPIV system was designed and built in-house at the University of Sydney. The experimental investigations described in this work revealed some interesting features of the environmental flows. The applicability and versatility of TPIV for these flows were demonstrated. The measurements allowed for the quantification and visualisation of the turbulence in the flows and hence shed light on the physics behind them.

The loss of central vision subsequent to macular disease is often extremely debilitating. People with central field loss (CFL) must use other peripheral areas of the retina in order to see; areas with inferior resolution capacity, which are also affected by off-axis optical errors. The overall aim of the work encompassed by this thesis was to identify and evaluate methods of improving vision for people with CFL; with focus on the effects of off-axis optical correction and stimulus motion on resolution acuity and contrast sensitivity. Off-axis optical errors were measured using a commercially-available COAS-HD VR open-view aberrometer. We used adaptive psychophysical methods to evaluate grating resolution acuity and contrast sensitivity in the peripheral visual field; drifting gratings were employed to   measure the effect of motion on these two measures of visual performance. The effect of sphero-cylindrical correction and stimulus motion on visual performance in healthy eyes and in subjects with CFL was also studied; in addition, the effect of adaptive optics aberration correction was examined in one subject with CFL. The COAS-HD aberrometer provided rapid and reliable measurements of off-axis refractive errors. Correction of these errors gave improvements in low-contrast resolution acuity in subjects with higher amounts of oblique astigmatism. Optical correction also improved high-contrast resolution acuity in most subjects with CFL, but not for healthy subjects. Adaptive optics correction improved both high and low contrast resolution acuity in the preferred retinal locus of a subject with CFL. The effect of stimulus motion depended on spatial frequency; motion of 7.5 Hz improved contrast sensitivity for stimuli of low spatial frequency in healthy and CFL subjects. Motion of 15 Hz had little effect on contrast sensitivity for low spatial frequency but resulted in reduced contrast sensitivity for higher spatial frequencies in healthy subjects. Finally, high-contrast resolution acuity was relatively insensitive to stimulus motion in the periphery. This thesis has served to broaden the knowledge regarding peripheral optical errors, stimulus motion and their effects on visual function, both in healthy subjects and in people with CFL. Overall it has shown that correction of off-axis refractive errors is important for optimizing peripheral vision in subjects with CFL; the use of an open-view aberrometer simplifies the determination of these errors. In addition, moderate stimulus motion can have a beneficial effect on contrast sensitivity for objects of predominantly low spatial frequency.

Overview: Optical concepts as they relate to the ophthalmologic correction of vision in corneal laser vision correction and intraocular lens design was examined. Purpose: The interaction between the excimer laser and residual corneal tissue in laser vision correction produces unwanted side effects. Understanding the origin of these artifacts can lead to better procedures. Furthermore, accommodating intraocular lenses offer a potential for eliminating presbyopia. Understanding the properties of a new accommodating intraocular lens incorporating a deformable interface may lead to advances in cataract surgery. Introduction: Corneal surface irregularities following laser refractive procedures are commonly seen. They regularly result in a patient’s decreased best corrected visual acuity and decreased contrast sensitivity. These changes are only seen in biologic tissue and the etiology has been elusive. A thermal response has been theorized and was investigated in this research. In addition, intraocular lenses using a mechanically deforming interface to change their power in order to duplicate natural accommodation have been developed. The deforming interface(s) induce optical aberrations due to irregular deformations. Design efforts have centered on minimizing these deformations. Both of the ophthalmic applications have been analyzed using finite element analysis (FEA) to understand their inherent optical properties. Methods: FEA modeling of thermal theory has been applied to verify that excimer laser induced collagen contraction creates corneal surface irregularities and central islands. A mathematical model which indicates the viability of the theory was developed. The modeling results were compared to post ablation changes in eyes utilizing an excimer (ArF 193 nm), as well as non-ablative thermal heating in eyes with a CO₂ laser. Addition modeling was performed on an Intraocular lens prototype measuring of actuation force, lens power, interface contour, optical transfer function, and visual Strehl ratio. Prototype verified mathematical models were utilized to optimize optical and mechanical design parameters to maximize the image quality and minimize the required force. Results: The predictive model shows significant irregular central buckling formation and irregular folding. The amount of collagen contraction necessary to cause significant surface changes is very small (0.3%). Uniform scanning excimer laser ablation to corneal stroma produces a significant central steepening and peripheral flattening in the central 3mm diameter. Isolated thermal load from uniform CO₂ laser irradiation without ablation also produces central corneal steepening and paracentral flattening in the central 3mm diameter. The iterative mathematical modeling based upon the intraocular lens prototype yielded maximized optical and mechanical performance through varied input mechanical and optical parameters to produce a maximized visual Strehl ratio and a minimized force requirement. Conclusions: The thermal load created by laser irradiation creates a characteristic spectrum of morphologic changes on the porcine corneal stromal surface which correlates to the temperature rise and is not seen inorganic, isotropic material. The highly similar surface changes seen with both lasers are likely indicative of temperature induced transverse collagen fibril contraction and stress re-distribution. Refractive procedures which produce significant thermal load should be cognizant of these morphological changes. The optimized intraocular lens operates within the physiologic constraints of the human eye including the force available for full accommodative amplitude using the eye’s natural focusing feedback, while maintaining image quality in the space available. Optimized optical and mechanical performance parameters were delineated as those which minimize both asphericity and actuation pressure. The methodology combines a multidisciplinary basic science approach from biomechanics, optical science, and ophthalmology to optimize an intraocular lens design suitable for preliminary trials.

The purpose of this study was to assess the effects of refractive vision correction through laser surgery (LASIK & PRK) of adults of working age (22-55). This study examined and compared the symptoms of depression, stress perception, and self-esteem prior to surgery and one month after surgery, when sufficient healing has occurred. Research has shown that vision impairment has been reported to be one of the 10 most significant causes of disability in the United States, and, even though clinicians are encouraged to assess emotional response to vision loss, the psychological factors that that play a role in adjustment to vision loss have not been sufficiently studied.

L’Institut Clément Ader Albi (ICAA) et l’Institut von Karman (IVK) mènent depuis un certain nombre d’années des travaux sur la radiométrie IR dans le but de faire de la thermographie quantitative (mesure de température vraie sans contact). Ces travaux ont permis d’explorer les potentialités de plusieurs bandes spectrales : 8-12µm, 3-5µm et plus récemment la bande 0,75-1,7µm (proche IR) à l’aide de caméras CCD (Si) ou VisGaAs. Les travaux effectués dans ce domaine spectral ont permis de mettre en évidence un certains nombre de perturbations renforcées par les hautes températures(T>800°C). Cette thèse aborde de façon détaillée le traitement d’un certain nombre de grandeurs d’influence liées à la mesure de différents paramètres dans le domaine du proche IR mais également étendus aux domaines du visible et de l’IR. La première de ces grandeurs est l’émissivité dont le traitement a déjà été abordé par d’autres études. La seconde grandeur d’influence touche plus particulièrement à la localisation des points chauds sur l’objet et la distorsion du champ de température apportée par les effets convectifs présents autour d’un objet à haute température, elle est le coeur de cette thèse. En effet, lorsqu’une pièce chaude se trouve dans un milieu ambiant beaucoup plus froid, il se crée un gradient de température et donc d’indice de réfraction autour de la pièce. Or les caméras travaillant dans les différentes bandes spectrales vont être plus ou moins sensibles à ces variations d’indices de réfraction du fait de la dépendance de l’indice optique avec la longueur d’onde et de la résolution spatiale de la caméra utilisée. Ce phénomène, appelé effet mirage, entraîne inévitablement une déformation des informations spatiales reçues par la caméra. Le but de cette thèse a donc été d’estimer et de proposer une première approche pour corriger l’erreur faite sur la mesure de température et/ou de déformation faites par caméras sur des pièces chaudes. La démarche générale du travail a donc été dans un premier temps de calculer le champ de température autour de l’objet considéré en se ramenant d’abord à des cas simplifiés. On en a déduit alors le champ de réfraction entraînant une « déformation » de l’objet, en faisant le lien entre T et n. Cette étape correspond à l’approche numérique de notre étude. Cette étape numérique a été réalisé à l’aide d’un outil de lancer de rayons développée à l’ICA. L’approche expérimentale a consisté à l’utilisation de méthodes telle que la BOS (Background Oriented Schlieren), la PIV, la srtioscopie afin de déduire le champ de déplacements provoqué par le panache convectif. Ces résultats ont été comparés à la méthode numérique et ceci pour différentes longueurs d’ondes. Enfin, une stratégie de correction d’images perturbées a été abordé à l’aide de méthodes telles que la transformée d’Abel inverse afin de remonter au champ d’indice de réfraction 2D axisymétrique à partir d’une déformation plane.

碩士
國立中正大學
地震研究所暨應用地球物理研究所
97
Compare to single element traditional ultrasonic probe, The phased array source which has several elements is widely used in medical images and nondestructive testing (NDT), Because of its excellent controllable, so we can transmit any direction wavefront by time shift. The synthetic aperture focusing technique (SAFT)is use in traditional ultrasonic probe, and total focusing method (TFM)is use in phased array probe. Both of synthetic aperture focusing technique and total focusing method are a way to improve acoustic image. In nondestructive testing, we usually need to face the problem of refraction. So in this paper we will combine TFM and refraction correction in order to improve acoustic image. Finally, using the phased array probe with transmitting time shift, TFM and refraction correction can built the high resolution 3D image volume.

碩士
國立中正大學
光機電整合工程研究所
106
Myopia is considered an urgent public health problem due to the impact of the global population and the burden of visual disability. An estimated 1.5 billion people were affected in 2010. Myopia is the most common cause of permanent visual impairment and is expected to increase by nearly 5 billion by 2050. Based on the peripheral refractive theory, this study designed a contact lens that can change the peripheral refraction of the retina,and established a measurement system that can measure the refractive state of the eyeball. The ASAP optical simulation software was used to analyze the retina under different refractive conditions. The image, together with the optimization, calculates the refractive power vector as the basis for correcting the effect. The purpose of this study is to cause relative myopia or peripheral hyperopia to control the growth of the axial growth of the eye to control the development of myopia. According to the results, the fourth-order spherical aberration peripheral refractive lens model constructed in this study is used, which has a good corrective effect on myopia control. Keywords: peripheral refraction, lens design, myopia control

博士
國立中央大學
地球物理學系
82
Results obtained in this study indicated that the internal precision of ME5000 distance measuring system, is about ±(0.1+0.1‧D)mm, where D is distance in km. An uncertainty of external precision in the absolute length system of light speed, as indicated from a comparison of the EOM results with Vaisala interference results - i.e., the most accurate method of determining the baseline length. Furthmore, its stability and accuracy has become the foundation for examining the atmospheric refraction correction for a medium - range EDM in the study. Due to long distance, the temperature, pressure and relative humidity are normally taken at the ends of the line during EDM. The averages of temperature, pressure and relative humidity from endpoints measurments are used to represent the true values along the wavepath length. As a consequence, the errors may cause a great restriction for the accuracy of EDM. This study, as based on the theory of atmospheric temperature model of Angus-Leppan and Brunner (1980), primarilly aims at analyzing the successive EDM data in Hsin Chu Medium-Range baseline as well as proposing a more practical and suitable temperature model for local area. Consequently, the error of group refractive index can be reduced and the accuracy improved. Furthermore, multi-layer atmospheric potential temperature model based on Webb (1964) was included to evaluate the additional correction when the elevation difference of EDM line is over the Obukhov length. This could be of help to raise the accuracy of EDM in Geodesy and the detection of crust deformation in Geophysics.

碩士
逢甲大學
電機工程學系
104
This paper proposes a multi-layer structure of RGP contact lenses design for peripheral refractive error correction of myopia. The structure is a combination of free-form、even-aspherical and biconic surface. This article describes contact lenses design procedure to correct visual aberration, such as defocus、coma and astigmatism, from the 〖30〗^° temporal side to the 〖30〗^° nasal side. Compared to a conventional contact lens, our design can simultaneously correct the defocus on central field and peripheral field on the retina. It expands the clear visual scope and avoids the further deterioration of myopia. The greatest feature of this design is that we combine three layers together. The first surface is biconic for correcting astigmatism, the second is even-aspherical for correcting high-order aberrations, and the third surface is of free-form to correct off-axis defocus at retina, the last surface is spherical with a radius of curvature matching the front surface of cornea. This design provides more flexibility and optimizable parameters to correct high order aberrations, while correcting the defocus on peripheral field. Thus achieve a better visual image quality, finally field at 0°、±10°、±20°、±30° which cutoff frequency is sequentially 110lp/mm, 35lp/mm, 20lp/mm and 15lp/mm of MTF values have reached 0.3.

碩士
逢甲大學
視光科技碩士在職學位學程
106
The purpose of this study was to develop a new technique of vision correction and promote the visual comfort. The single-pole brainwave extractor and tonometer were applicated to measure the results of the vision correction using the full-correction (MPMVA) lens or the spherical equivalent lens. In the study, the volunteers with astigmatic refractive error wearing MPMVA lens or the spherical equivalent lens received the exam of the single-pole brainwave extractor. When the brainwave exam revealed the focus, the vision was clear. The tonometry were performed after wearing the lens for 15 minutes. About the result, the elevated intraocular pressure (3.33mmHg, right eye and 2.00mmHg, left eye) after wearing the spherical equivalent lens comparing to MPMVA lens were found in the group of low astigmatic refractive error. In the group of high astigmatic refractive error, the elevated intraocular pressure of the right eye (1.33mmHg) was found. The change of the intraocular pressure revealed the difference of MPMVA lens and the spherical equivalent lens. To promote the visual comfort, we suggest using MPMVA lens, especially in the group of low astigmatic refractive error.

BACKGROUND: The human eye is an incredible organ, capable of focusing and detecting light that passes through its specialized structures. These organs are responsible for the sensation of vision and are crucial to the ability to function and operate during daily life. Loss of the sense of vision can result in serious deficits that greatly reduce the quality of a person’s life. One of the most prevalent causes of vision impairment in the world is refractive error. Although this is a common and relatively simple problem to fix with modern technology, ophthalmologists are continuously searching for new methods of treating people’s eyes to correct refractive errors and improve vision. There are several popular methods for correcting refractive errors, including traditional glasses, contact lenses, and laser vision correction. Laser vision correction is the most modern method for improving visual acuity deficits caused by refractive errors. The two most favored techniques for laser vision correction are laser assisted in site keratomileusis (LASIK) and photorefractive keratectomy (PRK). The performance of these procedures requires a laser treatment input to be calculated based on the patient’s refractive error. These laser treatment inputs are often determined using a nomogram. Nomograms are mathematical functions utilizing a graphical display to calculate a given value based on a set of parameters. Nomograms are crucial for safe and effective LASIK and PRK procedures and there is much interest in enhancing these algorithms to improve the refractive and visual acuity outcomes. OBJECTIVES: The objective of the study was to determine if a newer, more complex laser vision correction nomogram could generate laser treatment inputs better than another more traditional nomogram in terms of refractive and visual acuity outcomes. METHODS: The study included 109 eyes belonging to 59 patients. Fifty-one eyes belonging to 28 patients were operated on using the Wellington nomogram and 58 eyes belonging to 31 patients were operated on using the Internet-based refractive analysis (IBRA) nomogram. Visual acuity and refractive outcomes were recorded at a six-week follow-up evaluation. Data were analyzed using statistical tests to determine significant values. RESULTS: No statistically significant difference was found between the recorded visual acuity and refractive outcomes of eyes operated on using the Wellington and IBRA nomograms. CONCLUSIONS: The two nomograms were found to perform at equal efficacy and to reach the established standards for safety. Although no significant difference was found between the two nomogram outcomes it is possible that there were variables limiting the external validity of the statistical analysis. With extra time, additional cases, and better sample matching the study could be expanded and developed to provide a more reliable and more representative dataset to elucidate conclusions with greater impact.
2022-06-07T00:00:00Z

Yes
Purpose To determine whether dizziness and falls rates change due to routine cataract surgery and to determine the influence of spectacle type and refractive factors. Methods Self-reported dizziness and falls were determined in 287 patients (mean age of 76.5 ± 6.3 years, 55% females) before and after routine cataract surgery for the first (81, 28%), second (109, 38%) and both eyes (97, 34%). Dizziness was determined using the short-form of the Dizziness Handicap Inventory. Six-month falls rates were determined using self-reported retrospective data. Results The number of patients with dizziness reduced significantly after cataract surgery (52% vs 38%; χ2 = 19.14, p < 0.001), but the reduction in the number of patients who fell in the 6-months post surgery was not significant (23% vs 20%; χ2 = 0.87, p = 0.35). Dizziness improved after first eye surgery (49% vs 33%, p = 0.01) and surgery on both eyes (58% vs 35%, p < 0.001), but not after second eye surgery (52% vs 45%, p = 0.68). Multivariate logistic regression analyses found significant links between post-operative falls and change in spectacle type (increased risk if switched into multifocal spectacles). Post-operative dizziness was associated with changes in best eye visual acuity and changes in oblique astigmatic correction. Conclusions Dizziness is significantly reduced by first (or both) eye cataract surgery and this is linked with improvements in best eye visual acuity, although changes in oblique astigmatic correction increased dizziness. The lack of improvement in falls rate may be associated with switching into multifocal spectacle wear after surgery.
This work was supported by The Dunhill Medical Trust(grant number SA14/0711).

No
Following aberroscopy, aspheric front surface soft contact lenses (SCLs) were custom-made to correct spherical refractive error and ocular spherical aberration (SA) of 18 myopic and five hypermetropic subjects (age, 20.5 . 5 yr). On-eye residual aberrations, logMAR visual acuity, and contrast sensitivity were compared with the best-correcting spectacle lens, an equally powered standard SCL, and an SCL designed to be aberration free in air. Custom-made and spherical SCLs reduced SA ( p . 0.001; p . 0.05) but did not change total root-meansquare (rms) wave-front aberration (WFA). Aberration-free SCLs increased SA ( p . 0.05), coma ( p . 0.05), and total rms WFA. Visual acuity remained unchanged with any of the SCL types compared with the spectacle lens correction. Contrast sensitivity at 6 cycles/degree improved with the custom-made SCLs ( p . 0.05). Increased coma with aspheric lens designs and uncorrected astigmatism limit the small possible visual benefit from correcting ocular SA with SCLs.

碩士
國立交通大學
電子物理學系
84
The diffractive lens is characteristic of thinness and lightness, and cost effective. The diffractive lens has the same imaging principle as refractive lens. In the traditional optical design, since a single lens has too much aberration, we need two or more refractive lensesto correct the aberration, but now we can easily use a single diffractivelens to improve the performance of a single lens. The aberration of a diffractive lens can be evaluated with the aberration formula of a refrctivelens in which the refrctive index is taken to be infinite. In this thesis, at first we will describe the aberrationfomula of the diffractive lens and simulate the imaging of the optical system.Then we describe how to make a diffractive lens by using the IC technology.At last we measure and evaluate the imaging quality of the optical system.

BACKGROUND: Laser vision correction (LVC) developed as a more permanent alternative to other forms of refractive error correction. In the last several decades, visual outcomes of corneal refractive surgeries like LVC have improved dramatically with the discovery of new technologies and techniques designed to make the patient experience more comfortable and worthwhile. LVC has been shown to safely and effectively treat refractive errors in myopic and hyperopic eyes, with gradually improving outcomes and safety measures. However, it is important to note whether specific excimer lasers impart the same level of safe, effective treatments for patients as technology advances. OBJECTIVE: This study aims to identify whether any statistically significant difference exists in the visual and refractive outcomes of hyperopic laser vision correction using two excimer laser platforms, the VISX STAR S4 IR® and the WaveLight® EX500, and to determine whether either laser shows any statistically significant difference in the rate of repeat surgery within one year post-operatively. METHODS: Using EMR data collected from December 2008 through December 2016, distance and near visual acuity outcomes for hyperopic eyes treated with LASIK, LASEK, or PRK were compared at one month and up to one year post-operatively. Distance eyes were compared separately from monovision (near-targeted) eyes for visual acuity; however, if manifest refraction post-operative data were available, they were used to identify whether any difference existed in the refractive outcomes in either category. The number of enhancements (repeat surgeries) was also tabulated. X2 Tests of Independence were used to determine statistical significance. RESULTS: Visual acuity outcomes in distance eyes at one month post-operatively showed similar trends between the two lasers, with 54% of the 267 VISX- and 60% of the 119 EX500-treated eyes presenting with UCVA of 20/20 or better. Eyes available for follow-up within one year post-operatively kept with this trend; 98 (51%) VISX- and 58 (67%) EX500-treated, eyes had UCVA measured at 20/20 or better. For monovision (treated for reading vision) eyes, 29 (47%) eyes and 19 (54%) of VISX- and EX500-treated eyes, respectively, read J1+ by one month post-operatively. By one year, 16 (39%) and 3 (21%) of available eyes read J1+ after treatment with the VISX and EX500 respectively. The relative enhancement rate was 7.82% (28 eyes) on the VISX and 4.19% (7 eyes) on the EX 500. CONCLUSION: Overall, visual outcomes of laser vision correction for hyperopic patients did not differ consistently between the two lasers. Only distance-treated eyes measured up to one year post-operatively showed a statistically significant difference between the two lasers. The visual and, more importantly, the refractive outcomes were statistically similar at both one month and up to one year post-operatively irrespective of treatment type. Enhancement rate between the two lasers also showed no differences. Both lasers are similarly safe and effective for treating hyperopia and hyperopic astigmatism.
2018-01-11T00:00:00Z