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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.
241

Association of anthropometric measures across the life-course with refractive error and ocular biometry at age 15 years

Bruce, A., Ghorbani Mojarrad, Neema, Santorelli, G. 13 July 2020 (has links)
Yes / Background A recent Genome-wide association meta-analysis (GWAS) of refractive error reported shared genetics with anthropometric traits such as height, BMI and obesity. To explore a potential relationship with refractive error and ocular structure we performed a life-course analysis including both maternal and child characteristics using data from the Avon Longitudinal Study of Parents and Children cohort. Methods Measures collected across the life-course were analysed to explore the association of height, weight, and BMI with refractive error and ocular biometric measures at age 15 years from 1613children. The outcome measures were the mean spherical equivalent (MSE) of refractive error (dioptres), axial length (AXL; mm), and radius of corneal curvature (RCC; mm). Potential confounding variables; maternal age at conception, maternal education level, parental socio-economic status, gestational age, breast-feeding, and gender were adjusted for within each multi-variable model. Results Maternal height was positively associated with teenage AXL (0.010 mm; 95% CI: 0.003, 0.017) and RCC (0.005 mm; 95% CI: 0.003, 0.007), increased maternal weight was positively associated with AXL (0.004 mm; 95% CI: 0.0001, 0.008). Birth length was associated with an increase in teenage AXL (0.067 mm; 95% CI: 0.032, 0.10) and flatter RCC (0.023 mm; 95% CI: 0.013, 0.034) and increasing birth weight was associated with flatter RCC (0.005 mm; 95% CI: 0.0003, 0.009). An increase in teenage height was associated with a lower MSE (− 0.007 D; 95% CI: − 0.013, − 0.001), an increase in AXL (0.021 mm; 95% CI: 0.015, 0.028) and flatter RCC (0.008 mm; 95% CI: 0.006, 0.010). Weight at 15 years was associated with an increase in AXL (0.005 mm; 95% CI: 0.001, 0.009). Conclusions At each life stage (pre-natal, birth, and teenage) height and weight, but not BMI, demonstrate an association with AXL and RCC measured at age 15 years. However, the negative association between refractive error and an increase in height was only present at the teenage life stage. Further research into the growth pattern of ocular structures and the development of refractive error over the life-course is required, particularly at the time of puberty.
242

Modeling the Complex Refractive Index of CdxZn1-xo by Spectrophotometric Characterization: An Evolutionary Approach

Falanga, Matthew 01 January 2007 (has links)
The complex refractive index is reported at room temperature for CdxZn1_xO thin film alloys for Cd composition up to 0.16. The CdxZn1_xO epilayers were grown by molecular-beam epitaxy on smooth ZnO/GaN/sapphire lattice templates. Transmission spectra were recorded by spectrophotometry in the 350-800nm wavelength range. The refractive index and extinction coefficient were derived by an evolutionary algorithm, which optimizes the Sellmeier and Forouhi-Bloomer dispersion models by a least-squares fitting to the experimental data.
243

Surface Modification of Multimaterial Multifunctional Fibers Enabling Biosensing Applications

Lopez Marcano, Ana Graciela 27 June 2018 (has links)
During the last decades, the continuing need for faster and smaller sensors has indeed triggered the rapid growth of more sophisticated technologies. This has led to the development of new optical-based sensors, able to detect and measure different phenomena using light. Furthermore, material processing technologies and micro fabrication methods have exponentially advanced, allowing engineers and scientists to develop new and more complex sensors on optical fibers platforms; specifically attractive for life science and biomedical research. All these substantial developments have brought biosensors to a point where multifunctionality is needed, this has led to envision the "Lab-on-Fiber" concept. Which promotes the integration of different sensing components into a single platform, an optical fiber. In this work, an integrated system with non-conventional polymer optical fibers and their further surface modification has been developed. With these different approaches, electrodes, hollow channels and plasmonic nanostructures can be incorporated into a single optical fiber-based sensor, allowing for both electrical and optical sensing with the capabilities of tuning and signal enhancement thanks to the metallic nanostructures. Different fiber substrates can be designed and modified in order to satisfy multiple requirements for a wide variety of applications. / MS / Silica optical fibers have been used since the 1960’s to guide optical signals, such as light, with low losses through long distances; making them an attractive platform to use in large communication systems. However, over the past couple of decades researchers have been trying to implement these low-loss platforms in sensing devices for many different fields, such as environmental and structural monitoring, and chemical and biomedical research. Unfortunately, their high brittleness has prompted researchers to introduce different materials in the same technology, leveraging the development of multimaterial non-conventional fibers. Where different polymers and even metals have replaced silica as the structural material, making these fibers more cost-affordable, flexible, and allow for multi-sensing capabilities of both electrical and optical signals. Although these multimaterial fibers are able to transmit light, they need to be functionalized or modified in order for them to be able to sense different phenomena occurring in their surrounding media. This can be achieved by integrating small particles or structures onto the fibers end-faces, these small structures are known as plasmonic nanostructures. When light (electromagnetic radiation) travels through a fiber and interacts with the free (conduction) electrons of a metallic nanostructure, it leads to a coupling that results in collective oscillations, which produce strong enhancement of the local electromagnetic fields surrounding the nanostructures. The latter can be easily detected with the help of an optical spectrum analyzer that iv stores the transmitted light as a function of the transmitted wavelength. Noble metals like gold and silver produce unprecedented electromagnetic field enhancements and are also biocompatible, making them very attractive in biosensing applications. In this research metallic plasmonic nanostructures were deposited on the end face of multimaterial polymer fibers to enhance the optical properties and potentially the electrical properties as well, creating new sensing devices. The enhancement produced by these structures was studied with both experimental measurements and theoretical simulations. The results demonstrate that the nanostructures investigated in this work can indeed enhance the optical properties of the used polymer fibers, enabling them to work as sensing probes for a many different applications, especially biosensing research.
244

Transient axial length change during the accommodation response in young adults

Mallen, Edward A.H., Hampson, Karen M., Kashyap, Priti January 2006 (has links)
No / The aims of the research may be outlined as follows: to measure the degree of transient axial elongation during the accommodation response in emmetropic and myopic young adults. To evaluate the effect of refractive error and accommodative demand on transient axial elongation of the eye. Axial length of the right eye was measured in 30 emmetropes and 30 myopes, by using the IOLMaster (Carl Zeiss Meditec, Inc., Dublin, CA), while accommodative stimuli of 0, 2, 4 and 6 D were presented with a Badal optometer. Axial length increased in both emmetropic and myopic subjects during short periods of accommodative stimulation. Greater transient increases in axial length were observed in myopic than in emmetropic subjects. The mean axial elongation with a 6-D stimulus to accommodation was 0.037 mm in emmetropes and 0.058 mm in myopes (P = 0.02). The degree of transient axial elongation correlated well with the stimulus to accommodation in emmetropes and myopes. Anterior chamber depth decreased, on average, by 0.19 mm in emmetropes and 0.18 mm in myopes when observing a 6-D stimulus to accommodation. During relatively short periods of accommodative stimulation, axial length increases in both emmetropic and myopic young adults. At higher levels of accommodative stimulation, a significantly greater transient increase in axial length is observed in myopic subjects than in their emmetropic counterparts.
245

Correcting ocular spherical aberration with soft contact lenses.

Cox, Michael J., Dietze, Holger H. January 2004 (has links)
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.
246

Vision and visual history in elite/near-elite level cricketers and rugby-league players

Barrett, Brendan T., Flavell, Jonathan C., Bennett, S.J., Cruickshank, Alice G., Mankowska, Aleksandra, Harris, J.M., Buckley, John 10 November 2017 (has links)
Yes / Background: The importance of optimal and/or superior vision for participation in high-level sport remains the subject of considerable clinical research interest. Here we examine the vision and visual history of elite/near-elite cricketers and rugby-league players. Methods: Stereoacuity (TNO), colour vision, and distance (with/without pinhole) and near visual acuity (VA) were measured in two cricket squads (elite/international-level, female, n=16; near-elite, male, n=23) and one professional rugby-league squad (male, n=20). Refractive error was determined, and details of any correction worn and visual history were recorded. Results: Overall, 63% had their last eye-examination within 2 years. However, some had not had an eye examination for 5 years, or had never had one (near-elite-cricketers: 30%; rugby-league players: 15%; elite-cricketers: 6%). Comparing our results for all participants to published data for young, optimally-corrected, non-sporting adults, distance VA was ~1 line of letters worse than expected. Adopting α=0.01, the deficit in distance-VA deficit was significant, but only for elite-cricketers (p<0.001) (near-elite cricketers, p=0.02; rugby-league players, p=0.03). Near-VA did not differ between subgroups or relative to published norms for young adults (p>0.02 for all comparisons). On average, stereoacuity was better than in young adults, but only in elite-cricketers (p<0.001; p=0.03, near-elite-cricketers; p=0.47, rugby-league -players). On-field visual issues were present in 27% of participants, and mostly (in 75% of cases) comprised uncorrected ametropia. Some cricketers (near-elite: 17.4%; elite: 38%) wore refractive correction during play but no rugby-league player did. Some individuals with prescribed correction choose not to wear it when playing. Conclusion: Aside from near stereoacuity in elite-cricketers, these basic visual abilities were not better than equivalent, published data for optimally-corrected adults. 20-25% exhibited sub-optimal vision, suggesting that the clearest possible vision might not be critical for participation at the highest levels in the sports of cricket or rugby-league. Although vision could be improved in a sizeable proportion of our sample, the impact of correcting these, mostly subtle, refractive anomalies on playing performance is unknown. / Funded by the UK’s Biotechnology and Biological Sciences Research Council (BBSRC) grants BB/J018163/1, BB/J016365/1 and BB/J018872/1.
247

CLEAR - Orthokeratology

Vincent, S.J., Cho, P., Chan, K.Y., Fadel, D., Ghorbani Mojarrad, Neema, González-Méijome, J.M., Johnson, L., Kang, P., Michaud, L., Simard, P., Jones, L. 10 November 2021 (has links)
No / Orthokeratology (ortho-k) is the process of deliberately reshaping the anterior cornea by utilising specialty contact lenses to temporarily and reversibly reduce refractive error after lens removal. Modern ortho-k utilises reverse geometry lens designs, made with highly oxygen permeable rigid materials, worn overnight to reshape the anterior cornea and provide temporary correction of refractive error. More recently, ortho-k has been extensively used to slow the progression of myopia in children. This report reviews the practice of ortho-k, including its history, mechanisms of refractive and ocular changes, current use in the correction of myopia, astigmatism, hyperopia, and presbyopia, and standard of care. Suitable candidates for ortho-k are described, along with the fitting process, factors impacting success, and the potential options for using newer lens designs. Ocular changes associated with ortho-k, such as alterations in corneal thickness, development of microcysts, pigmented arcs, and fibrillary lines are reviewed. The safety of ortho-k is extensively reviewed, along with an overview of non-compliant behaviours and appropriate disinfection regimens. Finally, the role of ortho-k in myopia management for children is discussed in terms of efficacy, safety, and potential mechanisms of myopia control, including the impact of factors such as initial fitting age, baseline refractive error, the role of peripheral defocus, higher order aberrations, pupil size, and treatment zone size. / The CLEAR initiative was facilitated by the BCLA, with financial support by way of Educational Grants for collaboration, publication and dissemination provided by Alcon and CooperVision.
248

Additive Manufacturing of Multi-dimensional Diffractive Elements

Junyu Hua (20347530) 10 January 2025 (has links)
<p dir="ltr">A diffractive optical element (DOE) can manipulate the light to generate the desired profile or shape with micro-structure patterns to alter the phase of the passed light. They are widely used and applied in various experimental and commercial systems because of their complex light manipulation capability, compact and lightweight designs, and holographic imaging ability. </p><p dir="ltr">There are many ways to make DOEs but it is hard to manufacture high precision DOEs with low cost, simple procedures, and capability for 3D structures. The current fabrication of DOEs mainly focuses on nanofabrication techniques, especially photolithography. These methods have a very high resolution and accuracy in nanoscale, but usually require expensive equipment and are limited to planar structures. Additive manufacturing is a low-cost, layer-based manufacturing technique, which is very strong in forming 3D structures. However, the resolution and accuracy of most 3D printers are limited to a micrometer scale, which is not small enough for the diffraction of visible light.</p><p dir="ltr">This research aims to understand the mechanics of modulating the phase of DOEs and improve the manufacturing process of 3D printing to achieve better resolution. Two Photon Polymerization (TPP) and Vat Photopolymerization (VPP) 3D printing techniques were investigated and improved to fabricate application-driven designs from 1D to 2D structures. Different strategies and methods such as drop coating, design of lattice structure, and exposure time controlling, were developed to manipulate the physical structure and material properties to control the phase modulation of DOEs. The results pave the way for the future application of 3D printing to fabricate complicated 3D DOEs. </p><p><br></p>
249

"Phase-Correlation Based Displacemnt-Metrology" - Few Investigations

Diwan, C Yogesh 07 1900 (has links) (PDF)
No description available.
250

Risk Factors Associated with the Occurrence of Refractive errors among Secondary School Children in Malamulele Community, Limpopo Province.

Khoza, Hllawulani Lizzy 09 1900 (has links)
MPH / Department of Public Health / See the attached abstract below

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