Modelling electrical stimulation of the human retina

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dc.contributor.advisor Vaghefi, E en
dc.contributor.advisor Trew, M en
dc.contributor.advisor Dokos, S en Shalbaf Hosseinabadi, Farzaneh en 2017-08-10T22:39:02Z en 2017 en
dc.identifier.uri en
dc.description.abstract Retinal prosthetic devices have been trialled in patients suffering from outer retinal degenerative diseases. Encouraging results have been reported, from light perception, recognition of familiar objects, as well as more complex level of perception such as alphabet recognition and reading. However, with a given device the same level of success is not achieved by all patients. The underlying reason, while still not well understood, has been attributed to the state of the disease in the recipient and effective electrode placements during surgery. We believe that developing patient-specific models of the human retina can provide a non-invasive tool to predict the response of individual retinae to electrical stimulation, and possibly assist optimizing retinal implant parameters and enhancing their performance. So far, the anatomical retinal variations between individuals and retinal structural changes due to the onset and progression of the disease have not been included in computational models of retinal electrical stimulation. Hence, their effects on device performance have not been explored yet. The primary objective of this thesis was to develop a patient-specific model of human retinal geometry, from optical coherence tomography (OCT) images, and investigate the possible effect of anatomical variations between individuals on retinal prosthesis performance. A population of five healthy and five diseased volunteers were scanned using OCT imaging, and patient-specific computational models of their retinal geometry were developed. In this model, an array of five hexapolar electrodes configuration was placed in the sub-retinal space at three different retinal regions, at the sub-foveal, at 1 mm eccentricity, and at 2 mm eccentricity from the central fovea. The computed activation threshold was determined for individual electrodes at each implantation site, and the results were compared within the population study. It is shown that anatomical variations between individuals alters the electrode distance to target cells, which in turn changes the 3D current distribution through the retinal layers, and ultimately affects activation threshold within and across subjects. Our observations indicate that the same device with a fixed level of stimulus current will not perform the same in different patients. Hence, to ensure consistent performance, stimulus current should be tuned for each electrode in each individual. Also, it is found that the sub-foveal and 1 mm eccentricity sites of implantations requires a lower activation threshold compared to 2 mm eccentricity positions, suggesting that these two regions can provide higher performance in future clinical applications. en
dc.publisher ResearchSpace@Auckland en
dc.relation.ispartof PhD Thesis - University of Auckland en
dc.relation.isreferencedby UoA99264957406002091 en
dc.rights Items in ResearchSpace are protected by copyright, with all rights reserved, unless otherwise indicated. Previously published items are made available in accordance with the copyright policy of the publisher. en
dc.rights.uri en
dc.rights.uri en
dc.title Modelling electrical stimulation of the human retina en
dc.type Thesis en Bioengineering en The University of Auckland en Doctoral en PhD en
dc.rights.holder Copyright: The author en
dc.rights.accessrights en
pubs.elements-id 646706 en
pubs.record-created-at-source-date 2017-08-11 en

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