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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Predicting the power of an intraocular lens implant : an application of model selection theory

Diodati-Nolin, Anna C. January 1985 (has links)
No description available.
2

Predicting the power of an intraocular lens implant : an application of model selection theory

Diodati-Nolin, Anna C. January 1985 (has links)
No description available.
3

Linear optics of the pseudophakic eye

27 October 2008 (has links)
D.Phil. / That the eye is essentially a first-order optical instrument is evidenced by the success Gaussian optics has met with in optometry and ophthalmology. An unfortunate consequence of this approach is that a brief review of the literature on the topic of intraocular lens power calculation gives one the impression that the character of such a lens is described fully by its dioptric power. This is not so. Indeed, the idea that a thin refracting interface can somehow embody the optical character of the thick intraocular lens can, and in many ways has, limited the scope of intraocular lens power formula. The purpose of this dissertation is to apply the methods of linear algebra to the investigation of the first-order optical character of the stigmatic and astigmatic pseudophakic eye. This work attempts to lay a solid foundation for the study of the pseudophakic eye in the context of first-order astigmatic optics. While the majority of concepts and results of this dissertation are directly applicable to the study of the pseudophakic eye, an attempt has been made to ensure that the methods outlined in this work may be applied to the study of optical systems in the broader context of first-order optics. Central to this work are the members of the non-abelian symplectic group Sp(2n) under the operation of conventional matrix multiplication. The elements are evendimensional, non-singular symplectic matrices with unit determinant which are referred to here as ray transferences. These matrices act on the members of even-dimensional vector spaces so as to preserve a particular skew-symmetric, non-degenerate bilinear pairing referred to as the symplectic form. The laws that govern the operation of these matrices, the three symplectic relations, flow naturally from the structure of the symplectic group. From the ray transference four 2„e 2 fundamental properties of an optical system may be defined, the dilation A , the disjugacy B , the divergence C and the divarication D. A number of additional optical properties can be derived from the fundamental properties. Examples of derived properties include the dioptric power F , the negative of the divergence C and refractive state 0 F . The ray transference is used here in the derivation of a set of new intraocular lens formulae for the pseudophakic eye. These formulae are entirely general, working equally well in both stigmatic and astigmatic pseudophakic eyes in which additional (possibly astigmatic) intraocular devices may already be present. Formulae for both distant and near objects are provided. The constraints under which the divergence of a thick (possibly bitoric) intraocular lens is conserved despite changes in the lens are investigated. Furthermore, the constraints under which the refractive state of the pseudophakic is conserved in spite of changes in the thick intraocular lens are investigated. We find that there exist an infinite number of thick intraocular lenses that will produce a given refractive outcome, say emmetropia, in the pseudophakic eye. The basic theory of matrix differentiation with respect to a scalar variable is utilized in the study of the changes in the optical character of the pseudophakic eye following axial translation of a variety of intraocular lens systems. A novel method of representing the changes in the stigmatic and antistigmatic properties of refraction on account of axial translation and rotation of a toric intraocular lens in the astigmatic eye is presented and numerical examples are provided. The analysis permits the calculation of the ideal axial lens position and orientation in the astigmatic pseudophakic eye. Such methods will prove increasingly important in refractive data analysis, particularly in light of the development of continuously adjustable intraocular devices. / Prof. W.F. Harris
4

Visual Function and Mobility After Multifocal Versus Monofocal Intraocular Lens Implantation

Hall, Courtney D., Barnes, Claire S., Gutherie, Audrey H., Lynch, Mary G. 01 January 2021 (has links)
Clinical relevance: Mobility and fall risk may be important considerations in choosing between intraocular lenses. Background: Fall risk in older adults increases when wearing multifocal spectacles, but little is known about mobility among individuals with different types of intraocular lenses. This study compared visual function, fall risk and balance control following bilateral implantation of monofocal or multifocal intraocular lenses. Methods: This was a non-randomised, cross-sectional study involving adults with bilateral intraocular lenses. Participants completed questionnaires concerning physical functioning, fall history and balance-related confidence. Binocular visual acuity, contrast sensitivity (Pelli-Robson chart and computerized testing), depth perception and glare sensitivity were assessed. Physical performance measures included the Sensory Organization Test, preferred gait speed, Dynamic Gait Index and wayfinding in a virtual environment. Results: Fifteen participants (mean ± standard deviation, 67.1 ± 6.8 years) had monofocal intraocular lenses and 14 participants (68.1 ± 6.1 years) had multifocal intraocular lenses. Contrast sensitivity in the monofocal group was significantly better than that in the multifocal group (p = 0.02) at intermediate and high spatial frequencies. Contrast sensitivity of the monofocal group also was less affected by glare than the contrast sensitivity of the multifocal group, at an intermediate spatial frequency (p = 0.02). However, the multifocal group had significantly better Dynamic Gait Index scores (p = 0.04), even after controlling for perceived physical function. Conclusions: The participants with monofocal intraocular lenses generally had better contrast sensitivity than did those with multifocal intraocular lenses. However, the scores on a mobility test that is associated with fall risk were worse for those with monofocal lenses.
5

Limitations of correcting spherical aberration with aspheric intraocular lenses.

Dietze, Holger H., Cox, Michael J. January 2005 (has links)
No / Aspheric intraocular lenses (IOLs) are designed to correct spherical aberration in pseudophakic eyes. We predict the benefit from correcting spherical aberration based on simulations and aberrometry of pseudophakic eyes implanted with spherical IOLs. METHODS Ray tracing was performed through a model eye with an equi-biconvex spherical IOL and with a spherical aberration-correcting aspheric IOL. The IOLs were increasingly tilted and/or displaced, and the resulting transverse aberrations of 169 rays were transformed into Zernike coefficients for different pupil sizes. The benefit from correcting spherical aberration at individual mesopic pupils was investigated by canceling in the sets of Zernike coefficients for 41 eyes implanted with a spherical IOL. RESULTS Both the model eye and the real eye data predict that age-related miosis reduces spherical aberration in the eye implanted with a spherical IOL to approximately 1/3 of the spherical aberration at a 6-mm pupil. A reduction of similar magnitude occurs when spherical aberration-induced non-paraxial defocus is corrected by a spectacle lens. For natural mesopic pupils, canceling the Zernike coefficient improved the objective image quality at a rate similar to changing defocus by 0.05 diopters. Average centration and tilt levels diminish the lead of aspheric IOLs over spherical IOLs, depending on the direction of decentration. CONCLUSIONS The benefit from correcting spherical aberration in a pseudophakic eye is limited for some or all of the following reasons: wearing glasses, age-related miosis, tilt and decentration of IOL, small contribution of spherical aberration to all aberrations, and intersubject variability
6

Optical Performance Test & Analysis of Intraocular Lenses

Choi, Junoh January 2008 (has links)
Cataract is a condition in the eye that if left untreated, could lead to blindness. One of the effective ways to treat cataract is the removal of the cataractous natural crystalline lens and implantation of an artificial lens called an intraocular lens(IOL). The designs of the IOLs have shown improvements over the years to further imitate natural human vision. A need for an objective testing and analysis tool for the latest IOLs grow with the advancements of the IOLs.In this dissertation, I present a system capable of objective test and analysis of the advanced IOLs. The system consists of-Model eye into which an IOL can be inserted to mimic conditions of the human eye.-Modulation Transfer Function measurement setup capable of through-focus test for depth of field studies and polychromatic test for study of effects of chromatization.-Use of Defocus Transfer Function to simulate depth of field characteristic of rotationally symmetric multifocal designs and extension of the function to polychromatic conditions.-Several target imaging experiments for comparison of stray light artifacts and simulation using a non-sequential ray trace package.
7

Análise de qualidade óptica e performance visual em olhos implantados com lentes intraoculares asféricas neutras / Implantation of an aspherical intraocular lens

Santhiago, Marcony Rodrigues de 05 October 2012 (has links)
Objetivo: Determinar se o implante de uma determinada lente intraocular asférica resulta em redução das aberrações oculares e melhora da qualidade ótica e sensibilidade ao contraste sem que ocorra redução critica da profundidade de foco. Desenho: Estudo prospectivo, duplo-cego, randomizado. Métodos: Este estudo que incluiu 25 pacientes com catarata bilateral, uma LIO asférica foi implantada em um olho e uma LIO esférica no olho contralateral. Aberrações de maior ordem e parâmetros de qualidade ótica foram obtidos através de aberrômetro de retinoscopia dinâmica, 1 e 3 meses apos a cirurgia. Foi também medido a acuidade visual com e sem correção e a sensibilidade ao contraste. Acuidade visual para perto e distancia intermediaria foi obtida como forma de medida da profundidade de foco. Resultados: Não houve diferença estatisticamente significativa entre os grupos para acuidade visual corrigida e não corrigida 1 e 3 meses apos a cirurgia. Houve diferença estatisticamente significativa entre os grupos quanto a sensibilidade ao contraste sob condições fotópticas na frequência espacial de 12 ciclos por grau e sob condições mesópicas em todas as frequências espaciais estudadas. O grupo com a LIO Akreos AO obteve menores valores de aberrações de maior ordem totais e de aberração esférica com pupilas de 5 e 6 mm e melhores valores de qualidade ótica comparado ao grupo com LIO Akreos Fit (p <0.05). Não houve diferença significativa entre os grupos quando se investigou visão de perto e intermediaria corrigido para longe. Conclusões: A LIO asférica Akreos AO induziu menos aberrações de maior ordem além de produzir melhores parâmetros de qualidade ótica com melhores resultados de sensibilidade ao contraste em condições mesópicas sem redução critica de profundidade de foco quando comparado a LIO esférica Akreos Fit. / PURPOSE: To determine whether implantation of an aspherical intraocular lens (IOL) results in reduced ocular aberrations and improved optical quality and contrast sensitivity after cataract surgery without critical reduction of depth of focus. DESIGN: Double-blinded, randomized, prospective study. METHODS: In an intraindividual study of 25 patients with bilateral cataract, an aspherical IOL (Akreos Advanced Optic [AO]; Bausch & Lomb, Inc., Rochester, New York, USA) was implanted in one eye and a spherical IOL (Akreos Fit; Bausch & Lomb, Inc) in the fellow eye. Higher-order aberrations with a 5- and 6-mm pupil and optical quality parameters were measured with a dynamic retinoscopy aberrometer at 1 and 3 months after surgery. Uncorrected and best-corrected visual acuity and contrast sensitivity under mesopic and photopic conditions also were measured. Distancecorrected near and intermediate visual acuity were studied as a measurement of depth of focus. RESULTS: There was no statistically significant difference between eyes in uncorrected and best-corrected visual acuity at 1 and 3 months after surgery. There was a statistically significant between-group difference in contrast sensitivity under photopic conditions at 12 cycles per degree and under mesopic conditions at all spatial frequencies. The Akreos AO group obtained statistically significant lower values of higher-order aberrations and spherical aberration with 5- and 6-mm pupils and better optical quality parameters compared with the Akreos Fit group (P < .05). There was no significant difference in distance-corrected near and intermediate visual acuity between both groups. CONCLUSIONS: Aspherical aberration-free Akreos AO IOL induced significantly less higher-order aberrations and spherical aberration than the Akreos Fit. Contrast sensitivity under mesopic conditions and optical quality parameters were better with the Akreos AO with similar results of depth of focus.
8

Aphakic iris-claw (Artisan®/Verisyse) lens implantation in low-income African population.

Kruse, Carl-Heinz. January 2007 (has links)
Purpose: To test the viability of implanting the Artisan®/VerisyseTM lens in a low-income monocular aphakic African population with insufficient capsular support where contact lens wear is expensive and spectacle correction is not possible, by assessing the postoperative visual functions. To further assess whether adverse effects (e.g.: pigment dispersion with secondary glaucoma, prolonged uveitis) in patients with highly pigmented irises would be as low as with patients in European and American trials. Methods: A prospective, randomised, controlled clinical trial comparing outcomes in two groups of unilateral aphakic patients. The patients in the first group received an Artisan intra-ocular iris-claw lens as a secondary procedure while the second group remained aphakic (the current treatment status quo for public patients in KwaZulu-Natal province in South Africa). Follow-up was done for 1 year. Results: The study was terminated early due to ethical and statistical reasons. Nine treated and five control patients were included. Monocular uncorrected vision was significantly higher in the treatment group (P=0,012) and patient satisfaction was higher (p=0,002). Changes in other variables (intraocular pressure, angle pigmentation, change in cup-to-disc ratio, iris pigment changes and best spectacle corrected vision) were not significantly different between the two groups. Conclusion: The Artisan®/VerisyseTM lens is a feasible option for aphakic African patients with regard to visual outcome, safety and patient satisfaction. This form of refractive correction should be the standard for patients with no capsular support and where other options are too expensive or carry greater risk. / Thesis (M.Med.)-University of KwaZulu-Natal, Durban, 2007.
9

Análise de qualidade óptica e performance visual em olhos implantados com lentes intraoculares asféricas neutras / Implantation of an aspherical intraocular lens

Marcony Rodrigues de Santhiago 05 October 2012 (has links)
Objetivo: Determinar se o implante de uma determinada lente intraocular asférica resulta em redução das aberrações oculares e melhora da qualidade ótica e sensibilidade ao contraste sem que ocorra redução critica da profundidade de foco. Desenho: Estudo prospectivo, duplo-cego, randomizado. Métodos: Este estudo que incluiu 25 pacientes com catarata bilateral, uma LIO asférica foi implantada em um olho e uma LIO esférica no olho contralateral. Aberrações de maior ordem e parâmetros de qualidade ótica foram obtidos através de aberrômetro de retinoscopia dinâmica, 1 e 3 meses apos a cirurgia. Foi também medido a acuidade visual com e sem correção e a sensibilidade ao contraste. Acuidade visual para perto e distancia intermediaria foi obtida como forma de medida da profundidade de foco. Resultados: Não houve diferença estatisticamente significativa entre os grupos para acuidade visual corrigida e não corrigida 1 e 3 meses apos a cirurgia. Houve diferença estatisticamente significativa entre os grupos quanto a sensibilidade ao contraste sob condições fotópticas na frequência espacial de 12 ciclos por grau e sob condições mesópicas em todas as frequências espaciais estudadas. O grupo com a LIO Akreos AO obteve menores valores de aberrações de maior ordem totais e de aberração esférica com pupilas de 5 e 6 mm e melhores valores de qualidade ótica comparado ao grupo com LIO Akreos Fit (p <0.05). Não houve diferença significativa entre os grupos quando se investigou visão de perto e intermediaria corrigido para longe. Conclusões: A LIO asférica Akreos AO induziu menos aberrações de maior ordem além de produzir melhores parâmetros de qualidade ótica com melhores resultados de sensibilidade ao contraste em condições mesópicas sem redução critica de profundidade de foco quando comparado a LIO esférica Akreos Fit. / PURPOSE: To determine whether implantation of an aspherical intraocular lens (IOL) results in reduced ocular aberrations and improved optical quality and contrast sensitivity after cataract surgery without critical reduction of depth of focus. DESIGN: Double-blinded, randomized, prospective study. METHODS: In an intraindividual study of 25 patients with bilateral cataract, an aspherical IOL (Akreos Advanced Optic [AO]; Bausch & Lomb, Inc., Rochester, New York, USA) was implanted in one eye and a spherical IOL (Akreos Fit; Bausch & Lomb, Inc) in the fellow eye. Higher-order aberrations with a 5- and 6-mm pupil and optical quality parameters were measured with a dynamic retinoscopy aberrometer at 1 and 3 months after surgery. Uncorrected and best-corrected visual acuity and contrast sensitivity under mesopic and photopic conditions also were measured. Distancecorrected near and intermediate visual acuity were studied as a measurement of depth of focus. RESULTS: There was no statistically significant difference between eyes in uncorrected and best-corrected visual acuity at 1 and 3 months after surgery. There was a statistically significant between-group difference in contrast sensitivity under photopic conditions at 12 cycles per degree and under mesopic conditions at all spatial frequencies. The Akreos AO group obtained statistically significant lower values of higher-order aberrations and spherical aberration with 5- and 6-mm pupils and better optical quality parameters compared with the Akreos Fit group (P < .05). There was no significant difference in distance-corrected near and intermediate visual acuity between both groups. CONCLUSIONS: Aspherical aberration-free Akreos AO IOL induced significantly less higher-order aberrations and spherical aberration than the Akreos Fit. Contrast sensitivity under mesopic conditions and optical quality parameters were better with the Akreos AO with similar results of depth of focus.
10

Correção da presbiopia pseudofácica através da implantação secundária de diafragma estenopeico no sulco ciliar / Pseudophakic presbyopia correction through secondary implantation of pinhole diaphragm in the ciliary sulcus

Trindade, Claudio Lovaglio Cançado 16 April 2019 (has links)
INTRODUÇÃO: A presbiopia pseudofácica, imposta pela extração do cristalino e implantação de uma lente intraocular monofocal, representa uma relativa limitação da cirurgia de catarata moderna. Diversos métodos para compensação de tal fenômeno já foram descritos. Nesse estudo, avaliamos a eficácia de um implante intraocular estenopeico em promover ampliação da profundidade de foco, e seu impacto no desempenho visual. MÉTODOS: Foram selecionados 10 pacientes hígidos, com boa saúde ocular, previamente submetidos a cirurgia de catarata bilateral com implante de lente intraocular monofocal, os quais apresentavam limitação da acuidade visual para perto. Os pacientes foram submetidos a implantação monocular do diafragma intraocular estenopeico XtraFocus®, no sulco ciliar. As variáveis avaliadas foram acuidade visual, refração subjetiva, sensibilidade ao contraste, amplitude de pseudoacomodação (curva de defocus), estereopsia, campimetria computadorizada, teste de efeito Pulfrich, e avaliação subjetiva do desempenho visual, através da aplicação de questionário. RESULTADOS: Houve significativa melhora da acuidade visual para perto, com 7 pacientes alcançando acuidade visual sem correção para perto de 20/30, no olho operado. Não houve impacto significativo na refração subjetiva, sensibilidade ao contraste e estereopsia. A perimetria computadorizada evidenciou redução de sensibilidade retiniana difusa, no olho operado. A percepção subjetiva do desempenho visual após o tratamento foi favorável, com impacto positivo nas atividades diárias. Não foi observada indução de efeito Pulfrich. CONCLUSÕES: O implante estenopeico estudado foi capaz de promover ampliação da profundidade de foco, com aprimoramento da acuidade visual para perto. O implantação cirúrgica se mostrou segura, sem ocorrência de eventos adversos significativos. Os resultados sugerem que uma maior independência de óculos pode ser alcançada caso a técnica seja aplicada em pacientes portadores de miopia de pequena magnitude. Este achado está em conformidade com trabalhos prévios envolvendo dispositivos estenopeicos. Apesar da limitação à entrada de luz imposta pelo orifício estenopeico, a percepção de luminosidade não é proporcionalmente impactada. Entretanto, em condições de baixa luminosidade, pode haver uma percepção monocular de escuridão / INTRODUCTION: Pseudophakic presbyopia, imposed by crystalline lens extraction and implantation of an artificial monofocal intraocular lens (IOL), represents a relative limitation of modern cataract surgery. Several methods of compensation of this phenomenon have been proposed. In this study, we evaluate the efficacy of a pinhole intraocular implant in promoting depth of focus extension, and its impact in visual performance. METHODS: A selection of 10 healthy patients, with no ocular comorbidity, previously submitted to bilateral cataract surgery and monofocal IOL implantation, presenting with near vision limitation, was carried out. Patients underwent monocular implantation of the XtraFocus® pinhole implant, in the ciliary sulcus. Outcome variables were visual acuity, subjective refraction, contrast sensitivity, amplitude of pseudoaccommodation (defocus curve), stereoacuity, automated perimetry, Pulfrich effect testing and subjective visual performance evaluation with a questionnaire. RESULTS: A significant improvement in near visual acuity was observed, with 7 patients reaching 20/30 uncorrected near visual acuity, in the operated eye. There was no significant impact in subjective refraction, contrast sensitivity and stereoacuity. Automated perimetry revealed a reduction of overall retinal sensitivity, in the operated eye. Subjective assessment of visual performance was favourable, with positive impact in daily activities. Induction of Pulfrich effect was not observed. CONCLUSIONS: The pinhole implant evaluated in this study was able to provide depth of focus extension, and enhance near visual acuity. Surgical implantation was safe, with no occurrence of significant adverse events. Results suggest that a greater level of spectacle independence may be achieved if this approach is combined with low levels of myopia. This finding is in accordance with other studies involving small aperture optics. In spite of the reduction of light entrance caused by the pinhole implant, the overall brightness sensation is not proportionally impaired. However, under low light conditions, a monocular darkening perception can occur

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