000164435 001__ 164435
000164435 005__ 20190619003307.0
000164435 0247_ $$2doi$$a10.5075/epfl-thesis-5048
000164435 02470 $$2urn$$aurn:nbn:ch:bel-epfl-thesis5048-5
000164435 02471 $$2nebis$$a6379334
000164435 037__ $$aTHESIS
000164435 041__ $$aeng
000164435 088__ $$a5048
000164435 245__ $$aAnalysis of Factors Affecting the Performance of Retinal Prostheses Using Finite Element Modelling of Electric Field Distribution in the Retina
000164435 269__ $$a2011
000164435 260__ $$bEPFL$$c2011$$aLausanne
000164435 300__ $$a171
000164435 336__ $$aTheses
000164435 520__ $$aThis dissertation proposes a computational framework  targeted at improving the design of currently employed  retinal prostheses. The framework was used for analysing  factors impacting the performance of prostheses in terms of  electrical stimulation for retinal neurons, which might lead  to a perception of pixelated vision. Despite their  demonstrated effectiveness, the chronic and safe usage of  these retinal prostheses in human and animal trials is  jeopardised due to high stimulation thresholds. This is  related to the distance between the stimulating electrodes  and the retinal neurons resulting from the implantation  procedure. The major goal of this dissertation was to  evaluate the stimulation efficacy in current implantable  planar microelectrode-based retinal prostheses and  consequently demonstrate their weakness, thereby providing  scope for the development of future implants. The effect of geometrical factors i.e., electrode-retina  distance and electrode size on stimulation applied to the  retina by retinal prostheses was studied. To this end, a  finite element method based simulation framework to compute  electric field distribution in the retina was constructed. An  electrical model of the retina was an integral part of the  framework, essentially represented by a resistivity profile  of the multi-layered retina. The elements of a retinal  prosthesis were modelled by incorporating realistic electrode  sizes, an anatomical and electrical model of the retina, a  precise positioning of stimulation and return electrodes and  the location of the implant with respect to the retina  representing the epiretinal and subretinal stimulation  schemes. The simulations were carried out both in quasi-static and  direct current (DC) modes. It was observed that  electrode-electrolyte interface and tissue capacitance could  be safely neglected in our model based on the magnitude of  the applied voltage stimulus and frequencies under  consideration. Therefore, all simulations were conducted in  DC mode. Thresholds and lateral extents of the stimulation  were computed for electrode sizes corresponding to existing  and self-fabricated implants. The values and trends obtained  were in agreement with experiments from literature and our  collaborators at the les Hôpitaux Universitaires de  Genève (HUG). In the subretinal stimulation scheme,  the computed variation of impedance with electrode-retina  distance correlated well with time varying in vivo  impedance measurements in rats conducted in collaboration  with the Institut de la Vision, INSERM, Paris. Finally, it  was also reiterated that the currently employed retinal  prostheses are not very efficient due to a significant  distance between the stimulation electrode and the retinal  cells. In addition, I present a new experimental technique for  measuring the absolute and local resistivity profile in  high-resolution along the retinal depth, based on impedance  spectroscopy using a bipolar microprobe. This experiment was  devised to extract the resistivity profile of an embryonic  chick retina to construct an electrical model for the  simulation framework to simulate in vitro retinal  stimulation experiments conducted by HUG collaborators. We  validated the capability of the technique in rat and  embryonic chick retinas. In conclusion, the computational framework presented in  this dissertation is more realistic than those found in  literature, but represents only a preliminary step towards an  accurate model of a real implantation scenario in  vivo. The simulation results are in agreement with  results from clinical trials in humans for epiretinal  configuration (literature) and with in vitro results  for epiretinal and subretinal stimulation applied to chick  retinas (HUG). The developed simulation framework computes quantities  that can form a reference for quality control during surgery  while inserting implants in the eye and functionality checks  by electrophysiologists. Furthermore, this framework is  useful in deciding the specifications of stimulation  electrodes such as optimal size, shape, material, array  density, and the position of the reference electrode to name  a few. The work presented here offers to aid in optimising  retinal prostheses and implantation procedures for patients  and eventually contributes towards improving their quality of  life.
000164435 6531_ $$aSimulation Framework
000164435 6531_ $$aFinite Element Method
000164435 6531_ $$aElectrode-retina Distance
000164435 6531_ $$aRetinal Prosthesis
000164435 6531_ $$aMicroelectrodes
000164435 6531_ $$aTissue Resistivity Profiling
000164435 6531_ $$améthodes de simulation
000164435 6531_ $$asimulations par éléments finis
000164435 6531_ $$adistance électrode/rétine
000164435 6531_ $$aimplants rétiniens
000164435 6531_ $$amicroélectrodes
000164435 6531_ $$arésistivité tissulaire
000164435 700__ $$0242541$$g171587$$aKasi Raj, Sri Harsha
000164435 720_2 $$aRenaud, Philippe$$edir.$$g107144$$0240219
000164435 8564_ $$uhttps://infoscience.epfl.ch/record/164435/files/EPFL_TH5048.pdf$$zTexte intégral / Full text$$s10151733$$yTexte intégral / Full text
000164435 909C0 $$xU10324$$0252064$$pLMIS4
000164435 909CO $$pthesis-bn2018$$pthesis-public$$pDOI$$ooai:infoscience.tind.io:164435$$qGLOBAL_SET$$pSTI$$pthesis$$qDOI2
000164435 918__ $$dEDMI$$cIMT$$aSTI
000164435 919__ $$aLMIS4
000164435 920__ $$b2011
000164435 970__ $$a5048/THESES
000164435 973__ $$sPUBLISHED$$aEPFL
000164435 980__ $$aTHESIS