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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

Relationships between Visual Field Sensitivity and Spectral Absorption Properties of the Neuroretinal Rim in Glaucoma by Multispectral Imaging

Denniss, Jonathan, Schiessl, I., Nourrit, V., Fenerty, C.H., Gautam, R., Henson, D.B. 07 November 2011 (has links)
No / To investigate the relationship between neuroretinal rim (NRR) differential light absorption (DLA, a measure of spectral absorption properties) and visual field (VF) sensitivity in primary open-angle glaucoma (POAG). atients diagnosed with (n = 22) or suspected of having (n = 7) POAG were imaged with a multispectral system incorporating a modified digital fundus camera, 250-W tungsten-halogen lamp, and fast-tuneable liquid crystal filter. Five images were captured sequentially within 1.0 second at wavelengths selected according to absorption properties of hemoglobin (range, 570–610 nm), and a Beer-Lambert law model was used to produce DLA maps of residual NRR from the images. Patients also underwent VF testing. Differences in NRR DLA in vertically opposing 180° and 45° sectors either side of the horizontal midline were compared with corresponding differences in VF sensitivity on both decibel and linear scales by Spearman's rank correlation. The decibel VF sensitivity scale showed significant relationships between superior–inferior NRR DLA difference and sensitivity differences between corresponding VF areas in 180° NRR sectors (Spearman ρ = 0.68; P < 0.0001), superior-/inferior-temporal 45° NRR sectors (ρ = 0.57; P < 0.002), and superior-/inferior-nasal 45° NRR sectors (ρ = 0.59; P < 0.001). Using the linear VF sensitivity scale significant relationships were found for 180° NRR sectors (ρ = 0.62; P < 0.0002) and superior–inferior–nasal 45° NRR sectors (ρ = 0.53; P < 0.002). No significant difference was found between correlations using the linear or decibel VF sensitivity scales. Residual NRR DLA is related to VF sensitivity in POAG. Multispectral imaging may provide clinically important information for the assessment and management of POAG. / College of Optometrists (UK) PhD Studentship (JD), Central Manchester NHS Foundation Trust Grant RO1180, the Manchester Academic Health Sciences Centre (MAHSC), and the NIHR Manchester Biomedical Research Centre.
2

Predicting visual acuity from visual field sensitivity in age-related macular degeneration

Denniss, Jonathan, Baggaley, H.C., Astle, A.T. January 2018 (has links)
Yes / Purpose: To investigate how well visual field sensitivity predicts visual acuity at the same locations in macular disease, and to assess whether such predictions may be useful for selecting an optimum area for fixation training. Methods: Visual field sensitivity and acuity were measured at nine locations in the central 10° in 20 people with AMD and stable foveal fixation. A linear mixed model was constructed to predict acuity from sensitivity, taking into account within-subject effects and eccentricity. Cross validation was used to test the ability to predict acuity from sensitivity in a new patient. Simulations tested whether sensitivity can predict nonfoveal regions with greatest acuity in individual patients. Results: Visual field sensitivity (P < 0.0001), eccentricity (P = 0.007), and random effects of subject on eccentricity (P = 0.043) improved the model. For known subjects, 95% of acuity prediction errors (predicted − measured acuity) fell within −0.21 logMAR to +0.18 logMAR (median +0.00 logMAR). For unknown subjects, cross validation gave 95% of acuity prediction errors within −0.35 logMAR to +0.31 logMAR (median −0.01 logMAR). In simulations, the nonfoveal location with greatest predicted acuity had greatest “true” acuity on median 26% of occasions, and median difference in acuity between the location with greatest predicted acuity and the best possible location was +0.14 logMAR (range +0.04 to +0.17). Conclusions: The relationship between sensitivity and acuity in macular disease is not strongly predictive. The location with greatest sensitivity on microperimetry is unlikely to represent the location with the best visual acuity, even if eccentricity is taken into account. / College of Optometrists Postdoctoral Research Award (JD and ATA; London, UK) and National Institute for Health Research (NIHR) Postdoctoral Fellowship (ATA; London, UK). Presents independent research funded by the NIHR. / Research Development Fund Publication Prize Award winner, August 2018.
3

Central Visual Field Sensitivity Data from Microperimetry with Spatially Dense Sampling

Astle, A.T., Ali, I., Denniss, Jonathan 04 August 2016 (has links)
Yes / Microperimetry, also referred to as fundus perimetry or fundus-driven perimetry, enables simultaneous acquisition of visual sensitivity and eye movement data. We present sensitivity data collected from 60 participants with normal vision using gaze-contingent perimetry. A custom designed spatially dense test grid was used to collect data across the visual field within 13° of fixation. These data are supplemental to a study in which we demonstrated a spatial interpolation method that facilitates comparison of acquired data from any set of spatial locations to normative data and thus screening of individuals with both normal and non-foveal fixation (Denniss and Astle, 2016)[1].
4

Theoretical studies towards a ferroelectric organic field-effect transistor based on functional thiophene molecules

Luschtinetz, Regina 16 January 2013 (has links) (PDF)
Thin-film organic field effect transistors (OFETs) have attracted growing interest in recent years due to their promising electrical, optical and mechanical properties. Especially, oligothiophenes and their derivates are candidates with good prospects for application as the organic semiconducting material in such devices. They possess an extended, polarisable aromatic π-electron system that promotes a high structural arrangement of the molecules. The charge transport in the organic film is realised in the direction perpendicular to the plane of the thiophene rings via a hopping transport mechanism. Thus, a good π-π-overlap and a consequent stacking of the thiophene molecules in the film perpendicular to the gate substrate is essential to achieve excellent electric properties such as high charge carrier mobilities and low resistive losses. The highly polarisable thiophene-based molecules are also very attractive materials that are potentially applicable as the field-sensitive organic semiconducting component of a ferroelectric OFET device. In such a device, the dielectric gate element of a conventional OFET setup is substituted by a ferroelectric substrate. The electric field that is induced by the polarisation of the ferroelectric material serves as gate field and controlls the charge injection and charge density inside the device. In this thesis, thiophene-based molecules are investigated in detail with respect to their application as field-sensitive organic semiconducting component in a ferroelectric OFET device employing quantum-chemical ab initio and DFT-based methods. We demonstrate that the phosphonic acids can bind the organic molecules to the dielectric or ferroelectric material and well-anchored, robust self-assembled monolayers are formed. Furthermore, special focus is put on the influence of the intermolecular interactions among the organic molecules on the technologically relevant structural and electronic properties. It is found that the CN···HC hydrogen bond link the molecules into extended ribbons, but the π-π-stacking-stacking interaction is the main driving force in the self-assembly of the molecules. We also establish in detail the influence of the electric field on the phosphonic acid anchoring molecule and some quarterthiophene derivates. For the latter, the strongest field-sensitivity is obtained for an external electric field aligned parallel to the extension of the thiophene framework. Hence, they are suitable to act as the field-sensitive organic components in devices that take advantage of a band-gap engineering. Moreover, the present results emphasise the importance of the adsorption morphology of the molecules in the film in a π-stacked fashion with their longitudinal axis oriented parallel to the (orthonormal) electric field induced by the ferroelectric substrate.
5

Theoretical studies towards a ferroelectric organic field-effect transistor based on functional thiophene molecules

Luschtinetz, Regina 04 December 2012 (has links)
Thin-film organic field effect transistors (OFETs) have attracted growing interest in recent years due to their promising electrical, optical and mechanical properties. Especially, oligothiophenes and their derivates are candidates with good prospects for application as the organic semiconducting material in such devices. They possess an extended, polarisable aromatic π-electron system that promotes a high structural arrangement of the molecules. The charge transport in the organic film is realised in the direction perpendicular to the plane of the thiophene rings via a hopping transport mechanism. Thus, a good π-π-overlap and a consequent stacking of the thiophene molecules in the film perpendicular to the gate substrate is essential to achieve excellent electric properties such as high charge carrier mobilities and low resistive losses. The highly polarisable thiophene-based molecules are also very attractive materials that are potentially applicable as the field-sensitive organic semiconducting component of a ferroelectric OFET device. In such a device, the dielectric gate element of a conventional OFET setup is substituted by a ferroelectric substrate. The electric field that is induced by the polarisation of the ferroelectric material serves as gate field and controlls the charge injection and charge density inside the device. In this thesis, thiophene-based molecules are investigated in detail with respect to their application as field-sensitive organic semiconducting component in a ferroelectric OFET device employing quantum-chemical ab initio and DFT-based methods. We demonstrate that the phosphonic acids can bind the organic molecules to the dielectric or ferroelectric material and well-anchored, robust self-assembled monolayers are formed. Furthermore, special focus is put on the influence of the intermolecular interactions among the organic molecules on the technologically relevant structural and electronic properties. It is found that the CN···HC hydrogen bond link the molecules into extended ribbons, but the π-π-stacking-stacking interaction is the main driving force in the self-assembly of the molecules. We also establish in detail the influence of the electric field on the phosphonic acid anchoring molecule and some quarterthiophene derivates. For the latter, the strongest field-sensitivity is obtained for an external electric field aligned parallel to the extension of the thiophene framework. Hence, they are suitable to act as the field-sensitive organic components in devices that take advantage of a band-gap engineering. Moreover, the present results emphasise the importance of the adsorption morphology of the molecules in the film in a π-stacked fashion with their longitudinal axis oriented parallel to the (orthonormal) electric field induced by the ferroelectric substrate.

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