286 research outputs found

    Photovoltaic restoration of sight with high visual acuity

    Get PDF
    Patients with retinal degeneration lose sight due to the gradual demise of photoreceptors. Electrical stimulation of surviving retinal neurons provides an alternative route for the delivery of visual information. We demonstrate that subretinal implants with 70-μm-wide photovoltaic pixels provide highly localized stimulation of retinal neurons in rats. The electrical receptive fields recorded in retinal ganglion cells were similar in size to the natural visual receptive fields. Similarly to normal vision, the retinal response to prosthetic stimulation exhibited flicker fusion at high frequencies, adaptation to static images and nonlinear spatial summation. In rats with retinal degeneration, these photovoltaic arrays elicited retinal responses with a spatial resolution of 64 ± 11 μm, corresponding to half of the normal visual acuity in healthy rats. The ease of implantation of these wireless and modular arrays, combined with their high resolution, opens the door to the functional restoration of sight in patients blinded by retinal degeneration

    Characterization of Retinal Ganglion Cell Responses to Electrical Stimulation Using White Noise

    Get PDF
    Retinitis pigmentosa and age-related macular degeneration are two leading causes of degenerative blindness. While there is still not a definitive course of treatment for either of these diseases, there is currently the world over, many different treatment strategies being explored. Of these various strategies, one of the most successful has been retinal implants. Retinal implants are microelectrode or photodiode arrays, that are implanted in the eye of a patient, to electrically stimulate the degenerating retina. Clinical trials have shown that many patients implanted with such a device, are able to regain a certain degree of functional vision. However, while the results of these ongoing clinical trials have been promising, there are still many technical challenges that need to be overcome. One of the biggest challenges facing present implants is the inability to preferentially stimulate different retinal pathways. This is because retinal implants use large-amplitude current or voltage pulses. This in turn leads to the indiscriminate activation of multiple classes of retinal ganglion cells (RGCs), and therefore, an overall reduction in the restored visual acuity. To tackle this issue, we decided to explore a novel stimulus paradigm, in which we present to the retina, a stream of smaller-amplitude subthreshold voltage pulses. By then correlating the retinal spikes to the stimuli preceding them, we calculate temporal input filters for various classes of RGCs, using a technique called spike-triggered averaging (STA). In doing this, we found that ON and OFF RGCs have electrical filters, which are very distinct from each other. This finding creates the possibility for the selective activation of the retina through the use of STA-based waveforms. Finally, using statistical models, we verify how well these temporal filters can predict RGC responses to novel electrical stimuli. In a broad sense, our work represents the successful application of systems engineering tools to retinal prosthetics, in an attempt to answer one of the field’s most difficult questions, namely selective stimulation of the retina

    Doctor of Philosophy

    Get PDF
    dissertationHuman retinitis pigmentosa (RP) typically involves decades of progressive vision loss before some patients become blind, and prospective therapies target patients who have been blind for substantial time, even decades. Evaluations of molecular and cellular therapies have primarily employed short-lived mouse models lacking the scope of remodeling common in human RP. The Rho Tg P347L transgenic rabbit offers a unique opportunity to evaluate the primary degeneration event and subsequent progressive remodeling that ensues over a timespan that recapitulates the human disease phenotype. Retinas from a TgP347L rabbit model of human dominant RP and wild-type litter mates were harvested over an 8-year span and processed for transmission electron microscope connectomics, immunocytochemistry for a range of macromolecules, and computational molecular phenotyping for small molecules, including transport tracing with D-Asp. Early time points in the TgP347L rabbit recapitulate the established sequence of photoreceptor loss, retinal remodeling, and reprogramming, and also reveal progressive disruptions in Müller cell metabolism, where rather than observing a homogeneous glial population, chaotic metabolic signatures emerge. By 4 years, virtually all remnants of photoreceptors are gone and the neural retina manifests severe cell loss and near complete loss of glutamine synthetase, though glial glutamate transport persists. By 6 years, there is a global >90% neuronal loss. In some regions the retina is devoid of identifiable cells and replaced by unknown debris-like assemblies. Though the 6-year retina does have locations with recognizable neurons, all cell types are drastically reduced in number and some have altered metabolic phenotypes. These results are never seen in wt littermates, including rabbits which are 8 years old. Electron microscopic analysis using wide-field connectomics imaging of the 6-year TgP347L sample demonstrates some structurally normal synapses, indicating that survivor neurons in these regions are not quiescent despite the lack of sensory input for a substantial period of time. These results indicate that, although photoreceptor degeneration is the trigger, retinal remodeling ultimately gives way to neurodegeneration, which is a separate unrelenting disease process independent of the initial insult, closely resembling slow progressive CNS neurodegenerations. Indeed, both metabolic disruption and debris-related degeneration predicts the existence of a persistent neuropathy, and increases in ?-synuclein levels support a proteinopathy component. Remodeling and neurodegeneration progress until the retina is devoid of recognizable cells. There is no stable state into which the retina settles and no cell type is spared. This has profound implications for current therapeutics. There will likely be critical windows for implementation but, ultimately, suspension of neurodegenerative remodeling will be required for long-term success

    Analysis of Factors Affecting the Performance of Retinal Prostheses Using Finite Element Modelling of Electric Field Distribution in the Retina

    Get PDF
    This 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

    Physiology of circadian entrainment

    Get PDF
    Mammalian circadian rhythms are controlled by endogenous biological oscillators, including a master clock located in the hypothalamic suprachiasmatic nuclei (SCN). Since the period of this oscillation is of ∼24 h, to keep synchrony with the environment, circadian rhythms need to be entrained daily by means of Zeitgeber (“time giver”) signals, such as the light-dark cycle. Recent advances in the neurophysiology and molecular biology of circadian rhythmicity allow a better understanding of synchronization. In this review we cover several aspects of the mechanisms for photic entrainment of mammalian circadian rhythms, including retinal sensitivity to light by means of novel photopigments as well as circadian variations in the retina that contribute to the regulation of retinal physiology. Downstream from the retina, we examine retinohypothalamic communication through neurotransmitter (glutamate, aspartate, pituitary adenylate cyclase-activating polypeptide) interaction with SCN receptors and the resulting signal transduction pathways in suprachiasmatic neurons, as well as putative neuron-glia interactions. Finally, we describe and analyze clock gene expression and its importance in entrainment mechanisms, as well as circadian disorders or retinal diseases related to entrainment deficits, including experimental and clinical treatments.Fil: Golombek, Diego Andres. Universidad Nacional de Quilmes. Departamento de Ciencia y Tecnologia; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Rosenstein, Ruth Estela. Universidad de Buenos Aires. Facultad de Medicina. Departamento de Bioquímica Humana; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin

    Towards clinical trials of a novel Bionic Eye: Building evidence of safety and efficacy

    Get PDF
    In the quest for therapeutic solutions for the visually impaired, electrical stimulation of the retina is, and has been, the focus of intense research. Some of these efforts have led to the development of the Phoenix99 Bionic Eye, a device which combines promising technological features with novel stimulation strategies. For medical devices, considerable challenges must be overcome before they’re allowed to be trialled in their target population. The requirements for a study to be performed include the demonstration of a positive risk-benefit ratio of the research. The present dissertation is an attempt to address how pre-clinical trials in animals can be used to understand and minimise risks. A positive risk-benefit ratio means that the potential benefits of the research outweigh the risks of the intervention. In the case of retinal prostheses, the risks include the surgical intervention, the immune response to the device, the safety of the electrical stimuli, and the effects of device ageing. In this work, successful demonstration of the surgical safety and biocompatibility of passive Phoenix99 devices during long-term implantation in sheep called for the evaluation of the chronic effects of the novel stimulation paradigms it can deliver. As preparation for this study, the techniques used to evaluate the safety and efficacy of the stimuli in animals were refined. A systematic approach to minimise the impact of anaesthesia on the experimental results is presented, as well as a novel in vivo retinal recording technique. To maximise the clinical relevance of all animal trials, a computer model for the prediction of thresholds was developed. Finally, in vitro device ageing was performed to deepen our understanding of the design’s potential for long-term implantation. Protocols for a long-term device safety study in sheep and for an acute human trial are also presented, thus taking concrete and sensible steps towards the first clinical use of the Phoenix99 Bionic Eye

    Phenotypic Characterization with Software Development for Analysis of the Visual System in Animal Models of Neurodevelopmental Diseases

    Get PDF
    A neurofibromatose tipo 1 (NF1) é uma perturbação do desenvolvimento neurológico com implicações cognitivas adultas. Provoca anomalias do sistema nervoso central e afeta 1 em 3000 indivíduos em todo o mundo. Contudo, pouco se sabe sobre os efeitos no sistema visual e como estes podem estar associados a défices cognitivos e preveem a sua progressão. Neste trabalho, avalia-se as potenciais alterações na fisiologia da retina num modelo genético de murgalho de NF1, utilizando uma técnica neurofisiológica não invasiva, o eletroretinograma (ERG), para determinar o seu potencial diagnóstico. Como um indicador fiável da função da retina em resposta à luz, o ERG tem a capacidade de ajudar a nossa interpretação da fisiopatologia das perturbações do neurodesenvolvimento e neurodegenerativas. Os principais objetivos desta tese são a caracterização fenotípica do sistema visual num modelo animal de NF1 e o desenvolvimento de ferramentas informáticas (MATLAB e Phyton) para processamento de sinais, análise de forma de onda, extração de características, e classificação. Verificou-se que os parâmetros ERG relacionados principalmente com a atividade oscilatória inibitória revelam alterações subtis dependentes do sexo. Para vários potenciais oscilatórios, machos e fêmeas exibem alterações opostas associadas ao genótipo mutante. Além disso, as características do ERG foram utilizadas para formar um classificador de aprendizagem de máquina baseado nos aglomerados significativos encontrados para algumas interações entre indivíduos, um classificador que se destina a ser capaz de receber um sinal e devolver o provável diagnóstico.Neurofibromatosis type 1 (NF1) is a neurodevelopmental disorder with adult cognitive implications. It causes central nervous system anomalies and affects 1 in 3000 individuals worldwide. However, little is known about the effects on the visual system circuitry and how these may be associated with cognitive deficits and predicts its progression. In this work, it was evaluated the potential alterations in retinal physiology in a genetic mouse model of NF1, using a non-invasive neurophysiological technique, the electroretinogram (ERG), to ascertain its diagnostic potential. As a reliable indicator of retinal function in response to light, the ERG has the ability to aid our interpretation of the pathophysiology of neurodevelopmental and neurodegenerative disorders. The main objectives of this thesis are the phenotypic characterization of the visual system in an animal model of NF1 and the development of computer tools (MATLAB and Phyton) for signal processing, waveform analysis, feature extraction, and classification. This work found that ERG parameters mainly related to inhibitory oscillatory activity reveal subtle sex-dependent alterations. For various oscillatory potentials males and females exhibit opposite changes associated with the transgenic background. Furthermore, the ERG features were used to form a machine learning classifier based on the significant clusters found for some interactions between individuals, a classifier that is meant to be able to receive a signal and return the likely diagnosis
    corecore