11 research outputs found

    A multimodal investigation in eye movements

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    While functional magnetic resonance imaging (fMRI) has identified which regions of interest (ROIs) are functionally active during a vergence movement (inward or outward eye rotation), task-modulated coactivation between ROIs is less understood. This study tests the following hypotheses: (1) significant task-modulated coactivation would be observed between the frontal eye fields (FEFs), the posterior parietal cortex (PPC), and the cerebellar vermis (CV); (2) significantly more functional activity and task-modulated coactivation would be observed in binocularly normal controls (BNCs) compared with convergence insufficiency (CI) subjects; and (3) after vergence training, the functional activity and task-modulated coactivation would increase in CIs compared with their baseline measurements. A block design of sustained fixation versus vergence eye movements stimulates activity in the FEFs, PPC, and CV. fMRI data from four CI subjects before and after vergence training are compared with seven BNCs. Functional activity is assessed using the blood oxygenation level dependent (BOLD) percent signal change. Task-modulated coactivation is assessed using an ROI-based task modulated coactivation analysis that reveals significant correlation between ROIs

    Ocular accommodation in primary school children

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    Aim Clear near vision would seem vital for education. Existing literature has suggested an association between accommodation and education. However, this evidence base is limited and conflicting. Furthermore, a causal relationship between accommodation response (AR) and education has not been shown to date. This PhD thesis was funded by Fight for Sight charity as a “first step” to investigate typical accommodation in primary school children and establish if a relationship exists between accommodation and education. Should a relationship be identified, the results were designed to provide pilot data for further research to investigate causality. Methods Three studies were conducted: 1. A qualitative study, involving parents of primary school children, explored parental concerns regarding accommodation research. 2. During a controlled laboratory based study AR to a range of targets was objectively assessed using the Plusoptix PowerRefII photorefractor. The relationship between AR and academic ability markers was analysed; providing pilot data for a school based study. 3 A purpose built portable laboratory (incorporating a Plusoptix R09 photorefractor) was used to asses AR in participants, from a range of socio-economic backgrounds, to various targets in a community (school based) setting. AR was analysed in relation to reading and attention. xvii Results The qualitative study established that parents would be willing to participate in future accommodation research but exposed concerns regarding research duration. In both the laboratory and school studies increased AR was observed in response to complex targets. Accommodation was not related to performance on educational tests. Conclusions AR is influenced by target type. Under naturalistic conditions typical children will exert increased accommodation to more cognitively demanding targets. Accommodation does not appear correlated to reading ability or attention. Even very able readers appear to function with a degree of accommodative lag

    Accommodation: optical function and crystalline lens imaging

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    Esta tesis se centra en el estudio, por medio de varias técnicas in vivo, del proceso de acomodación del ojo humano. En primer lugar, haciendo uso de un sistema de Óptica Adaptativa, muestra que las aberraciones de alto orden disminuyen la precisión acomodativa, al mismo tiempo que tienden a incrementar las fluctuaciones de la acomodación. Por último, con un sistema de Tomografía de Coherencia Óptica de alta resolución, se hace imagen estática tridimensional del cristalino para diferentes demandas acomodativas. Del mismo modo, también se hace imagen dinámica bidimensional del cristalino durante la acomodación. El análisis de las imágenes permite obtener información de la respuesta acomodativa del ojo

    Light-assisted domain engineering, waveguide fabrication and microstructuring of lithium niobate

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    The thesis is focussing on the interaction of lithium niobate with UV and ultrafast laser radiation to achieve 1) ferroelectric domain inversion, 2) waveguide fabrication, and 3) surface microstructuring. Preferential ferroelectric domain inversion has been demonstrated by 'latent light-assisted poling' and 'inhibition of poling' using ultrafast laser irradiation at 400 nm and CW highly absorbed UV radiation (305..244 nm) respectively. The characteristics of the resultant domains have been experimentally investigated as a function of the fabrication conditions and a theoretical model have been proposed to explain the experimental observations. UV radiation in the 305 nm to 244 nm range have been used for the fabrication of optical waveguides in lithium niobate. The waveguiding characteristics and electro-optic response of the UV written optical channel waveguides have been investigated experimentally. Inhibition of poling and post processing has been used for the fabrication of ridge waveguide structures with enhanced refractive index change. Finally, a method for the fabrication of ultra-smooth lithium niobate single crystal photonic microstructures has been proposed. The method is based on surface tension reshaping of surface microstructures which are produced by preferential poling and subsequent etching. Whispering gallery mode resonators have been fabricated and characterised here

    Anterior segment topography and aberrations for clinical applications

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    En esta tesis se ha llevado a cabo el desarrollo de un Tomógrafo de Coherencia Óptica (OCT) para visualizar en alta resolución y cuantificar tridimensionalmente el segmento anterior del ojo y se ha adaptado el aberrómetro Trazado de Rayos Laser (LRT) para medir las aberraciones oculares en distintas condiciones: queratocono y su tratamiento con anillos intracorneales (ICRS), estimulando la acomodación y en pacientes con lentes intraoculares (IOL). En particular, (1) se analiza la geometría de la córnea y las aberraciones en pacientes con queratocono antes y después de la cirugía de ICRS, y se analiza la posición de los ICRS; (2) se evalúa por primera vez in vivo la topografía del cristalino con la acomodación; (3) se analiza por primera vez la posición tridimensional y el impacto visual de las IOL acomodativas; y (4) se analiza in vivo la aberración cromática longitudinal en pacientes con IOL.Instituto Universitario de Oftalmobiología Aplicad

    Updates on Myopia

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    This book is open access under a CC BY 4.0 license. This open access book discusses basic clinical concepts of myopia, prevention of progression and surgical treatments for myopia and pathological myopia. It also summarises the latest evidence and best practices for managing myopia, high myopia and its complications. Written by leading experts, the book addresses clinical diagnosis and interpretation of imaging modalities, and various complications of myopia such as glaucoma, choroidal neovascularization, retinal degeneration and cataracts. It is a valuable comprehensive resource for general and sub-specialist ophthalmologists as well as residents and ophthalmologists in training.

    Low-Toxicity Diacetone Acrylamide-Based Photopolymer For applications in Holography

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    Photopolymers are fast becoming one of the most popular holographic recording media due to their suitability for a wide range of holographic applications, such as sensors, diffractive optics and data storage. The majority of the investigated water-soluble holographic photopolymers are Acrylamide (AA) based. However, the toxic and carcinogenic nature of AA is a growing concern. In order for photopolymer recording media to be a viable option for holographic applications, efforts must be made to remove any occupational and environmental hazards involved in large-scale material development and device fabrication. The main objective of the work presented here is the development and characterisation of an environmentally friendly photopolymer for holographic applications which uses the non-toxic, non-carcinogenic monomer Diacetone Acrylamide (DA) as a substitute for AA in the photopolymer composition. The new DA photopolymer has been shown to achieve diffraction efficiency values of up to 95 % in transmission mode with refractive index modulation values of 3.5×10-3, and diffraction efficiencies of up to 38 % in the reflection regime with the incorporation of a chain transfer agent and after UV post exposure. Parameters such as shrinkage of the photopolymer layer and rate of polymerisation during the recording process have been quantified. The effect of the incorporation of the additives, namely glycerol and zeolite nanoparticles, on the holographic recording properties of the DA-based material has been investigated. A cytotoxicity comparison between the DA and AA photopolymers has also been carried out. The ability of the new photopolymer material to act as a gas sensor has been demonstrated. For the first time, reflection gratings recorded in the photopolymer have been successfully used as pressure-sensing devices, producing a visible and quantifiable colour change under exposure to different pressures

    Advances in Ophthalmology

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    This book focuses on the different aspects of ophthalmology - the medical science of diagnosis and treatment of eye disorders. Ophthalmology is divided into various clinical subspecialties, such as cornea, cataract, glaucoma, uveitis, retina, neuro-ophthalmology, pediatric ophthalmology, oncology, pathology, and oculoplastics. This book incorporates new developments as well as future perspectives in ophthalmology and is a balanced product between covering a wide range of diseases and expedited publication. It is intended to be the appetizer for other books to follow. Ophthalmologists, researchers, specialists, trainees, and general practitioners with an interest in ophthalmology will find this book interesting and useful
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