京都大学 / 0048 / 新制・課程博士 / 博士(医学) / 甲第20271号 / 医博第4230号 / 新制||医||1021(附属図書館) / 京都大学大学院医学研究科医学専攻 / (主査)教授 木村 剛, 教授 富樫 かおり, 教授 高橋 淳 / 学位規則第4条第1項該当 / Doctor of Medical Science / Kyoto University / DFAM

京都大学 / 0048 / 新制・課程博士 / 博士(医学) / 甲第21629号 / 医博第4435号 / 新制||医||1033(附属図書館) / 京都大学大学院医学研究科医学専攻 / (主査)教授 伊佐 正, 教授 柳田 素子, 教授 宮本 享 / 学位規則第4条第1項該当 / Doctor of Medical Science / Kyoto University / DFAM

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Spectral domain optical coherence tomography (OCT) is a powerful tool for measuring nanometer-scale displacement responses in the cochlea, as it is capable of volumetric imaging and vibrometry at a depth into a sample. The past decade has seen a wealth of OCT-measured displacement data from structures within the organ of Corti complex (OCC) that had previously been impossible to measure in vivo. These data have revealed surprising features of active intra-OCC motion but have not yet led to a complete understanding of cochlear amplification, the means by which active processes enhance the tuning and gain of the cochlear displacement responses in a level-dependent manner. Certain technical challenges arise from the properties of OCT imaging and vibrometry that obscure the interpretation of intra-OCC displacement measurements. In particular, OCT-measured responses are dependent on the orientation of the system's beam axis. The beam axis is generally chosen based on experimental convenience, and has no inherent relevance to the anatomy of the cochlea. This introduces two problems: 1) OCT-acquired images of the cochlea may be taken at skewed angles relative to the cochlea's naturally endowed anatomical coordinates, and 2) OCT-measured displacement responses are projections of a three-dimensional motion onto the beam axis. This thesis concerns the quantification of these effects on intra-OCC displacement measurements, as well as the development of methods to overcome these complications in vivo. In doing so, previously reported data that appear to disagree can be synthesized. I present a method by which the skew of OCT images relative to cochlear anatomy can be quantified, relating the OCT system's optical coordinates to the cochlear anatomy. With this method, I have shown that OCT images resembling familiar anatomical drawings of longitudinal cross-sections often capture a completely different anatomical slice of the cochlea. This leads to large quantitative shifts in phase responses when measuring displacements along a single beam axis, as opposed to what one would measure if s/he were measuring along an anatomically relevant axis. I have also provided a method by which to account for this phenomenon to capture structures related in some desired anatomical fashion. I then turn to the issue of projection of the three-dimensional cochlear motion onto the OCT beam axis. I have provided a method for reconstructing two- and three-dimensional displacement responses in the relevant anatomical directions by acquiring displacement measurements at multiple locations within the cochlea. In doing so, I have revealed that previously unexplained disagreements between measurements in different experimental preparations can be explained by competing components of motion being projected onto the single axis. I have also shown that motion at the junction between the outer hair cells and Deiters cells follows a lineal pattern, as opposed to non-degenerate elliptical patterns that would be expected of fluid motion in this region. This method requires the acquisition of data at many points within the OCC, making it significantly time-consuming. This makes it vulnerable to sample drift and deterioration, and reduces experimental yield. Certain applications of the method -- such as reconstructing displacement maps over a dense volume -- are thereby intractable. To address this problem, I have developed a compressed sensing method for vibrometry (CSVi). CSVi is a classical optimization method based on a total generalized variation signal prior, which is shown to out-perform methods using total variation and wavelet domain sparsity priors. I have also found that uniform sub-sampling schema offered significant performance benefits over random sub-sampling schema. I found that this CSVi method can reconstruct densely sampled displacement maps in the cochlea in vivo with less than 5% normalized mean square error, using only 10% of samples. While these methods offer new insight into interpretation of OCT displacement measurements, there is still a challenge in measuring the motion of the stereocilia of the hair cells. The stereocilia are too small to be imaged using OCT, and the proxy measurement of differential motion of the reticular lamina and tectorial membrane (between which the stereocilia lie) is not yet achievable in the gerbil base. Stereocilia motion is related to the transduction current through the hair cells, which is critical to understanding cochlear function. These currents lead to neurotransmitter release and active electromotile responses believed to be responsible for cochlear amplification. I present a model for studying another proxy measurement of the stereocilia motion -- the voltage in the cochlea's scala tympani, or cochlear microphonic (CM). This model of CM reveals that to match experimental data 1) stereocilia motion must be more sharply tuned than measured intra-OCC displacement responses, 2) the displacement-current gain of the mechano-electric transducer channels in vivo must be larger than what is measured in vitro by a factor of ~6, and 3) the hair cells at more basal locations of the cochlea must be compromised. These predictions offer insight into aspects of cochlear mechanics that are not easily probed using OCT.

Amblyopia is the leading cause of monocular visual impairment in children. Therapy for amblyopia is extremely beneficial in some children but ineffective in others. It is critical that the reasons for this discrepancy are understood. Emerging evidence indicates that current clinical protocols for the diagnosis of amblyopia may not be sufficiently sensitive in identifying individuals who, on more detailed examination, exhibit subtle structural defects of the eye. Presently, the magnitude of this problem is unknown. The aim of this study was to establish the prevalence of subtle retinal/optic nerve head defects in eyes diagnosed with amblyopia, to distinguish between possible explanations for the origin of such defects and to investigate the relationship between quantitative measures of retinal structure, retinal nerve fibre layer thickness and optic nerve head dimensions. Using the imaging technique of Optical Coherence Tomography (OCT) retinal structure has been investigated in detail, following the visual pathway across the retina from the fovea, via the paramacular bundle to the optic disc, where peripapillary retinal nerve fibre thickness has been imaged and subjected to detailed measures along with optic disc size and shape. The study formed two phases, the first imaging the eyes of visually normal adults and children, comparing them to amblyopes, both adults and children who had completed their treatment. The second phase, a longitudinal study, investigated retinal structure of amblyopic children undertaking occlusion therapy for the first time. By relating pre-therapy quantitative measures to the visual outcome the second phase of the study aimed to examine whether OCT imaging could identify children achieving a poor final outcome. The results show a clear picture of inter-ocular symmetry structure in all individuals, visually normal and amblyopic. Optic disc characteristics revealed no structural abnormalities in amblyopes, in any of the measured parameters, nor was there any association between the level of visual acuity and the measured structure. At the fovea differences were shown to occur in the presence of amblyopia, with thickening of the fovea and reduction of the foveal pit depth. The structural changes were found to be both bilateral and symmetrical with the fellow eye also affected. In the longitudinal phase of the study these changes were demonstrated to a greater extent in children who ¿failed¿ to respond to treatment. This bilateral, symmetrical structural change found at the fovea, which has not been previously reported, cannot therefore be the primary cause of the visual loss which has been diagnosed as amblyopia.

Despite advancements in percutaneous coronary intervention, stents are still limited by a 2% annual rate of in-stent restenosis (ISR) related to neointimal (NI) tissue proliferation. Efforts to prevent ISR formation remain the focus of ongoing work. Adenosine (ADO) is a purine nucleoside with integral roles in vascular homeostasis, though it has limited clinical application. ADO signals primarily via four receptors with ADO receptor-A2B (ADOR-A2B) considered to play an integral role in vascular healing. Dipyridamole (DP) is a commercially approved therapy known to improve vascular events and modulate adenosine biology. Our objectives with this study included (i) assessing whether ADO could serve as a biomarker of cardiac events; (ii) determine if DP could mitigate NI formation in a pre-clinical stent model; and, (iii) quantify the mechanisms of DP-related vasculoprotection, specifically related to ADOR-A2B. We assessed the analytic and biologic variability of circulating ADO levels in humans and demonstrated that circulating ADO was not predictive of cardiac events at one year following invasive coronary angiography. We then assessed whether modulation of adenosine biology with DP had therapeutic efficacy in a pre-clinical model. Utilizing meta-analysis, we confirmed the sustained effects of DP on vascular patency rates in both pre-clinical and clinical studies. We refined a pre-clinical rabbit model of stent implantation with assessment of stent healing by intravascular optical coherence tomography – with excellent translation to clinical observations. We then assessed DP in a pre-clinical model, demonstrating reduction in ISR and improved stent healing with DP compared to control. Last, we sought to elucidate the mechanisms behind the observed DP effects, specifically related to ADOR-A2B. In vivo, DP therapy demonstrated reduced NI smooth muscle cell (SMC) content. In vitro assessment of DP demonstrated dose-dependent inhibition of SMC proliferation and migration with alteration of SMC phenotypic switching, while selective modulation of ADOR-A2B and ADOR-A2B knockdown support an ADOR-A2B-mediated component to the observed DP effects. Adenosine biology is integral to vascular homeostasis. In humans, circulating adenosine levels in humans are not predictive of one year cardiovascular events. However, DP may improve vascular healing post stent implantation and warrants clinical evaluation for stent healing. The observed DP benefits may, in part, stem from ADOR-A2B modulation. ADOR-A2B is a viable target for assessment of small molecule modulation as a novel therapeutic target to improve vascular outcomes.

京都大学 / 新制・課程博士 / 博士(医学) / 甲第24877号 / 医博第5011号 / 新制||医||1068(附属図書館) / 京都大学大学院医学研究科医学専攻 / (主査)教授 川上 浩司, 教授 森田 智視, 教授 長船 健二 / 学位規則第4条第1項該当 / Doctor of Medical Science / Kyoto University / DFAM

Sensory adaptation to blur improves visual acuity under defocused conditions. This phenomenon has been successfully demonstrated using subjective measures of acuity and is known as blur adaptation. This study investigates aspects of the mechanism of blur adaptation in human vision using subjective and objective methods. Parafoveal visual acuity measured under defocused conditions demonstrates that blur adaptation is not limited to the fovea. The presence of the adaptive mechanism in the parafovea also suggests that the neural compensation that takes places under defocused conditions acts across a spatial range and is not limited to specific frequency bands. An evaluation of the contrast sensitivity function under defocus provides further evidence. Electrophysiological methods measure the effect of blur adaptation at the retina and at the visual cortex to provide objective evidence for the presence of the blur adaptation mechanism. Finally enhanced-depth imaging optical coherence tomography examines whether a period of prolonged defocus triggers any short-term changes in choroidal thickness in a similar manner to that reported in animal emmetropisation. / Engineering and Physical Sciences Research Council

Glaucoma is a leading cause of irreversible vision loss globally, and demands early and accurate diagnosis. OCT has become a key investigative technique in glaucoma, and, although it provides invaluable clinical support, detection of early glaucoma remains imperfect. Recent OCT developments enabled direct assessment of retinal nerve fibre bundle (RNFB) reflectance in en face OCT images. The technique has considerable potential in the assessment of glaucoma, yet it has limited clinical usability due to an incomplete understanding of RNFB features in healthy and glaucoma eyes and the lack of accepted methods to identify reflectance defects. This thesis aimed to better understand characteristics of RNFB reflectance in en face OCT imaging and to develop objective methods to extract defects in this domain. Structural and functional measures of glaucoma changes were collected in eyes with established glaucoma and age-similar controls. Results showed that the healthy configuration of RNFB varies across the retina and between different eyes. We developed a method for automated and objective examination of reflectivity changes in en face images. This method considers individual anatomy and varying RNFB configuration, and found more abnormalities than previous approaches. Measures of en face reflectance and conventional retinal nerve fibre layer thickness were strongly related. The agreement between changes of reflectance and visual function was moderate-to-good, and both testing domains presented concordant abnormalities in all tested eyes. Following further minimisation of artefacts in en face images, direct use of reflectance analysis or its combination with perimetry appear viable and with significant potential for clinical examination of glaucoma.