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Rahmani A, Eom K. Enhanced organic photovoltaic-based retinal prosthesis using a cathode-modified structure with plasmonic silver nanoparticles: a computational study. Front Cell Neurosci 2024; 18:1385567. [PMID: 38873618 PMCID: PMC11169897 DOI: 10.3389/fncel.2024.1385567] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2024] [Accepted: 05/13/2024] [Indexed: 06/15/2024] Open
Abstract
Introduction Organic interfaces have recently emerged as a breakthrough trend in biomedical applications, demonstrating exceptional performance in stimulating retinal neuronal cells owing to their high flexibility and compatibility with tissues. However, the primary challenge associated with organic photovoltaics is their low efficiency compared to that of their inorganic counterparts. Among different approaches, embedding plasmonic metal nanoparticles (NPs) in active or buffer layers can efficiently improve photovoltaic cell performance. Methods A cathode decorated with silver nanoparticles is introduced to increase the absorption Phenomenon and improve the interface performance as a computational study. In addition to embedding spherical silver nanoparticles in the active layer (A-AgNPs), a monolayer array of spherical AgNPs in the cathode electrode (K-AgNPs) is incorporated. In this configuration, the large K-AgNPs play dual roles: acting as cathode electrode and serving as plasmonic centers to increase light trapping and absorption. The bulk heterojunction PCPDTBT:PCBM is chosen as the active layer due to its favorable electronic properties. Results Our computational analysis demonstrates a notable 10% enhancement in the photovoltaic cell current density for the developed structure with K-AgNPs in contrast to without them. Additionally, the simulation results reveal that the modeled device achieves a two-fold efficiency of the bare photovoltaic cell (without A-AgNPs and K-AgNPs), which is particularly evident at a low intensity of 0.26 mW/mm2. Discussion This study aims to propose an efficient epiretinal prosthesis structure using a different strategy for plasmonic effects rather than conventional methods, such as incorporating NPs into the active or buffer layer. This structure can prevent the harmful side effects of using large metal NPs (r > 10 nm) in the active layer during exciton quenching, charge trapping, and recombination, which deteriorate the power conversion efficiency (PCE).
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Affiliation(s)
- Ali Rahmani
- Department of Electronics Engineering, College of Engineering, Pusan National University, Busan, Republic of Korea
- Department of Electronics, College of Electrical and Computer Engineering, Yadegar-e-Imam Khomeini (RAH) Shahre Rey Branch, Islamic Azad University, Tehran, Iran
| | - Kyungsik Eom
- Department of Electronics Engineering, College of Engineering, Pusan National University, Busan, Republic of Korea
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Corna A, Cojocaru AE, Bui MT, Werginz P, Zeck G. Avoidance of axonal stimulation with sinusoidal epiretinal stimulation. J Neural Eng 2024; 21:026036. [PMID: 38547529 DOI: 10.1088/1741-2552/ad38de] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2023] [Accepted: 03/28/2024] [Indexed: 04/11/2024]
Abstract
Objective.Neuromodulation, particularly electrical stimulation, necessitates high spatial resolution to achieve artificial vision with high acuity. In epiretinal implants, this is hindered by the undesired activation of distal axons. Here, we investigate focal and axonal activation of retinal ganglion cells (RGCs) in epiretinal configuration for different sinusoidal stimulation frequencies.Approach.RGC responses to epiretinal sinusoidal stimulation at frequencies between 40 and 100 Hz were tested inex-vivophotoreceptor degenerated (rd10) isolated retinae. Experiments were conducted using a high-density CMOS-based microelectrode array, which allows to localize RGC cell bodies and axons at high spatial resolution.Main results.We report current and charge density thresholds for focal and distal axon activation at stimulation frequencies of 40, 60, 80, and 100 Hz for an electrode size with an effective area of 0.01 mm2. Activation of distal axons is avoided up to a stimulation amplitude of 0.23µA (corresponding to 17.3µC cm-2) at 40 Hz and up to a stimulation amplitude of 0.28µA (14.8µC cm-2) at 60 Hz. The threshold ratio between focal and axonal activation increases from 1.1 for 100 Hz up to 1.6 for 60 Hz, while at 40 Hz stimulation frequency, almost no axonal responses were detected in the tested intensity range. With the use of synaptic blockers, we demonstrate the underlying direct activation mechanism of the ganglion cells. Finally, using high-resolution electrical imaging and label-free electrophysiological axon tracking, we demonstrate the extent of activation in axon bundles.Significance.Our results can be exploited to define a spatially selective stimulation strategy avoiding axonal activation in future retinal implants, thereby solving one of the major limitations of artificial vision. The results may be extended to other fields of neuroprosthetics to achieve selective focal electrical stimulation.
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Affiliation(s)
- Andrea Corna
- Institute of Biomedical Electronics, TU Wien, Vienna, Austria
| | | | - Mai Thu Bui
- Institute of Biomedical Electronics, TU Wien, Vienna, Austria
| | - Paul Werginz
- Institute of Biomedical Electronics, TU Wien, Vienna, Austria
| | - Günther Zeck
- Institute of Biomedical Electronics, TU Wien, Vienna, Austria
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Hou Y, Nanduri D, Granley J, Weiland JD, Beyeler M. Axonal stimulation affects the linear summation of single-point perception in three Argus II users. J Neural Eng 2024; 21:026031. [PMID: 38457841 PMCID: PMC11003296 DOI: 10.1088/1741-2552/ad31c4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2023] [Revised: 02/20/2024] [Accepted: 03/08/2024] [Indexed: 03/10/2024]
Abstract
Objective.Retinal implants use electrical stimulation to elicit perceived flashes of light ('phosphenes'). Single-electrode phosphene shape has been shown to vary systematically with stimulus parameters and the retinal location of the stimulating electrode, due to incidental activation of passing nerve fiber bundles. However, this knowledge has yet to be extended to paired-electrode stimulation.Approach.We retrospectively analyzed 3548 phosphene drawings made by three blind participants implanted with an Argus II Retinal Prosthesis. Phosphene shape (characterized by area, perimeter, major and minor axis length) and number of perceived phosphenes were averaged across trials and correlated with the corresponding single-electrode parameters. In addition, the number of phosphenes was correlated with stimulus amplitude and neuroanatomical parameters: electrode-retina and electrode-fovea distance as well as the electrode-electrode distance to ('between-axon') and along axon bundles ('along-axon'). Statistical analyses were conducted using linear regression and partial correlation analysis.Main results.Simple regression revealed that each paired-electrode shape descriptor could be predicted by the sum of the two corresponding single-electrode shape descriptors (p < .001). Multiple regression revealed that paired-electrode phosphene shape was primarily predicted by stimulus amplitude and electrode-fovea distance (p < .05). Interestingly, the number of elicited phosphenes tended to increase with between-axon distance (p < .05), but not with along-axon distance, in two out of three participants.Significance.The shape of phosphenes elicited by paired-electrode stimulation was well predicted by the shape of their corresponding single-electrode phosphenes, suggesting that two-point perception can be expressed as the linear summation of single-point perception. The impact of the between-axon distance on the perceived number of phosphenes provides further evidence in support of the axon map model for epiretinal stimulation. These findings contribute to the growing literature on phosphene perception and have important implications for the design of future retinal prostheses.
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Affiliation(s)
- Yuchen Hou
- Department of Computer Science, University of California, Santa Barbara, CA, United States of America
- Department of Psychological & Brain Sciences, University of California, Santa Barbara, CA, United States of America
| | - Devyani Nanduri
- Department of Biomedical Engineering, University of Southern California, Los Angeles, CA, United States of America
| | - Jacob Granley
- Department of Computer Science, University of California, Santa Barbara, CA, United States of America
| | - James D Weiland
- Department of Biomedical Engineering, University of Southern California, Los Angeles, CA, United States of America
- Department of Biomedical Engineering, University of Michigan, Ann Arbor, MI, United States of America
| | - Michael Beyeler
- Department of Computer Science, University of California, Santa Barbara, CA, United States of America
- Department of Psychological & Brain Sciences, University of California, Santa Barbara, CA, United States of America
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Muralidharan M, Guo T, Tsai D, Lee JI, Fried S, Dokos S, Morley JW, Lovell NH, Shivdasani MN. Neural activity of retinal ganglion cells under continuous, dynamically-modulated high frequency electrical stimulation. J Neural Eng 2024; 21:015001. [PMID: 38290151 DOI: 10.1088/1741-2552/ad2404] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2023] [Accepted: 01/30/2024] [Indexed: 02/01/2024]
Abstract
Objective.Current retinal prosthetics are limited in their ability to precisely control firing patterns of functionally distinct retinal ganglion cell (RGC) types. The aim of this study was to characterise RGC responses to continuous, kilohertz-frequency-varying stimulation to assess its utility in controlling RGC activity.Approach.We usedin vitropatch-clamp experiments to assess electrically-evoked ON and OFF RGC responses to frequency-varying pulse train sequences. In each sequence, the stimulation amplitude was kept constant while the stimulation frequency (0.5-10 kHz) was changed every 40 ms, in either a linearly increasing, linearly decreasing or randomised manner. The stimulation amplitude across sequences was increased from 10 to 300µA.Main results.We found that continuous stimulation without rest periods caused complex and irreproducible stimulus-response relationships, primarily due to strong stimulus-induced response adaptation and influence of the preceding stimulus frequency on the response to a subsequent stimulus. In addition, ON and OFF populations showed different sensitivities to continuous, frequency-varying pulse trains, with OFF cells generally exhibiting more dependency on frequency changes within a sequence. Finally, the ability to maintain spiking behaviour to continuous stimulation in RGCs significantly reduced over longer stimulation durations irrespective of the frequency order.Significance.This study represents an important step in advancing and understanding the utility of continuous frequency modulation in controlling functionally distinct RGCs. Our results indicate that continuous, kHz-frequency-varying stimulation sequences provide very limited control of RGC firing patterns due to inter-dependency between adjacent frequencies and generally, different RGC types do not display different frequency preferences under such stimulation conditions. For future stimulation strategies using kHz frequencies, careful consideration must be given to design appropriate pauses in stimulation, stimulation frequency order and the length of continuous stimulation duration.
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Affiliation(s)
| | - Tianruo Guo
- Graduate School of Biomedical Engineering, UNSW, Sydney, NSW 2052, Australia
| | - David Tsai
- Graduate School of Biomedical Engineering, UNSW, Sydney, NSW 2052, Australia
- School of Electrical Engineering & Telecommunications, UNSW, Sydney, NSW 2052, Australia
| | - Jae-Ik Lee
- Department of Neurosurgery, Massachusetts General Hospital and Harvard Medical School, Boston, MA, United States of America
| | - Shelley Fried
- Department of Neurosurgery, Massachusetts General Hospital and Harvard Medical School, Boston, MA, United States of America
| | - Socrates Dokos
- Graduate School of Biomedical Engineering, UNSW, Sydney, NSW 2052, Australia
| | - John W Morley
- Graduate School of Biomedical Engineering, UNSW, Sydney, NSW 2052, Australia
- School of Medicine, Western Sydney University, Penrith, NSW 2751, Australia
| | - Nigel H Lovell
- Graduate School of Biomedical Engineering, UNSW, Sydney, NSW 2052, Australia
- Tyree Institute of Health Engineering (iHealthE), UNSW, Sydney, NSW 2052, Australia
| | - Mohit N Shivdasani
- Graduate School of Biomedical Engineering, UNSW, Sydney, NSW 2052, Australia
- Tyree Institute of Health Engineering (iHealthE), UNSW, Sydney, NSW 2052, Australia
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Lavoie J, Besrour M, Lemaire W, Rouat J, Fontaine R, Plourde E. Learning to see via epiretinal implant stimulation in silicowith model-based deep reinforcement learning. Biomed Phys Eng Express 2024; 10:025006. [PMID: 37595568 DOI: 10.1088/2057-1976/acf1a5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2023] [Accepted: 08/18/2023] [Indexed: 08/20/2023]
Abstract
OBJECTIVE Diseases such as age-related macular degeneration and retinitis pigmentosa cause the degradation of the photoreceptor layer. One approach to restore vision is to electrically stimulate the surviving retinal ganglion cells with a microelectrode array such as epiretinal implants. Epiretinal implants are known to generate visible anisotropic shapes elongated along the axon fascicles of neighboring retinal ganglion cells. Recent work has demonstrated that to obtain isotropic pixel-like shapes, it is possible to map axon fascicles and avoid stimulating them by inactivating electrodes or lowering stimulation current levels. Avoiding axon fascicule stimulation aims to remove brushstroke-like shapes in favor of a more reduced set of pixel-like shapes. APPROACH In this study, we propose the use of isotropic and anisotropic shapes to render intelligible images on the retina of a virtual patient in a reinforcement learning environment named rlretina. The environment formalizes the task as using brushstrokes in a stroke-based rendering task. MAIN RESULTS We train a deep reinforcement learning agent that learns to assemble isotropic and anisotropic shapes to form an image. We investigate which error-based or perception-based metrics are adequate to reward the agent. The agent is trained in a model-based data generation fashion using the psychophysically validated axon map model to render images as perceived by different virtual patients. We show that the agent can generate more intelligible images compared to the naive method in different virtual patients. SIGNIFICANCE This work shares a new way to address epiretinal stimulation that constitutes a first step towards improving visual acuity in artificially-restored vision using anisotropic phosphenes.
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Affiliation(s)
- Jacob Lavoie
- Department of Electrical Engineering and Computer Engineering, Université de Sherbrooke, Sherbrooke, Quebec, J1K 2R1, Canada
| | - Marwan Besrour
- Department of Electrical Engineering and Computer Engineering, Université de Sherbrooke, Sherbrooke, Quebec, J1K 2R1, Canada
| | - William Lemaire
- Department of Electrical Engineering and Computer Engineering, Université de Sherbrooke, Sherbrooke, Quebec, J1K 2R1, Canada
| | - Jean Rouat
- Department of Electrical Engineering and Computer Engineering, Université de Sherbrooke, Sherbrooke, Quebec, J1K 2R1, Canada
| | - Réjean Fontaine
- Department of Electrical Engineering and Computer Engineering, Université de Sherbrooke, Sherbrooke, Quebec, J1K 2R1, Canada
| | - Eric Plourde
- Department of Electrical Engineering and Computer Engineering, Université de Sherbrooke, Sherbrooke, Quebec, J1K 2R1, Canada
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Hou Y, Nanduri D, Granley J, Weiland JD, Beyeler M. Axonal stimulation affects the linear summation of single-point perception in three Argus II users. MEDRXIV : THE PREPRINT SERVER FOR HEALTH SCIENCES 2023:2023.07.21.23292908. [PMID: 37546858 PMCID: PMC10402233 DOI: 10.1101/2023.07.21.23292908] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 08/08/2023]
Abstract
Purpose Retinal implants use electrical stimulation to elicit perceived flashes of light ("phosphenes"). Single-electrode phosphene shape has been shown to vary systematically with stimulus parameters and the retinal location of the stimulating electrode, due to incidental activation of passing nerve fiber bundles. However, this knowledge has yet to be extended to paired-electrode stimulation. Methods We retrospectively analyzed 3548 phosphene drawings made by three blind participants implanted with an Argus II Retinal Prosthesis. Phosphene shape (characterized by area, perimeter, major and minor axis length) and number of perceived phosphenes were averaged across trials and correlated with the corresponding single-electrode parameters. In addition, the number of phosphenes was correlated with stimulus amplitude and neuroanatomical parameters: electrode-retina and electrode-fovea distance as well as the electrode-electrode distance to ("between-axon") and along axon bundles ("along-axon"). Statistical analyses were conducted using linear regression and partial correlation analysis. Results Simple regression revealed that each paired-electrode shape descriptor could be predicted by the sum of the two corresponding single-electrode shape descriptors (p < .001). Multiple regression revealed that paired-electrode phosphene shape was primarily predicted by stimulus amplitude and electrode-fovea distance (p < .05). Interestingly, the number of elicited phosphenes tended to increase with between-axon distance (p < .05), but not with along-axon distance, in two out of three participants. Conclusions The shape of phosphenes elicited by paired-electrode stimulation was well predicted by the shape of their corresponding single-electrode phosphenes, suggesting that two-point perception can be expressed as the linear summation of single-point perception. The notable impact of the between-axon distance on the perceived number of phosphenes provides further evidence in support of the axon map model for epiretinal stimulation. These findings contribute to the growing literature on phosphene perception and have important implications for the design of future retinal prostheses.
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Affiliation(s)
- Yuchen Hou
- Department of Computer Science, University of California, Santa Barbara, CA
- Department of Psychological & Brain Sciences, University of California, Santa Barbara, CA
| | - Devyani Nanduri
- Department of Biomedical Engineering, University of Southern California, Los Angeles, CA
- Department of Biomedical Engineering, University of Michigan, Ann Arbor, MI
| | - Jacob Granley
- Department of Computer Science, University of California, Santa Barbara, CA
| | - James D Weiland
- Department of Biomedical Engineering, University of Michigan, Ann Arbor, MI
| | - Michael Beyeler
- Department of Computer Science, University of California, Santa Barbara, CA
- Department of Psychological & Brain Sciences, University of California, Santa Barbara, CA
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Kish KE, Yuan A, Weiland JD. Patient-specific computational models of retinal prostheses. Sci Rep 2023; 13:22271. [PMID: 38097732 PMCID: PMC10721907 DOI: 10.1038/s41598-023-49580-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2023] [Accepted: 12/09/2023] [Indexed: 12/17/2023] Open
Abstract
Retinal prostheses stimulate inner retinal neurons to create visual perception for blind patients. Implanted arrays have many small electrodes. Not all electrodes induce perception at the same stimulus amplitude, requiring clinicians to manually establish a visual perception threshold for each one. Phosphenes created by single-electrode stimuli can also vary in shape, size, and brightness. Computational models provide a tool to predict inter-electrode variability and automate device programming. In this study, we created statistical and patient-specific field-cable models to investigate inter-electrode variability across seven epiretinal prosthesis users. Our statistical analysis revealed that retinal thickness beneath the electrode correlated with perceptual threshold, with a significant fixed effect across participants. Electrode-retina distance and electrode impedance also correlated with perceptual threshold for some participants, but these effects varied by individual. We developed a novel method to construct patient-specific field-cable models from optical coherence tomography images. Predictions with these models significantly correlated with perceptual threshold for 80% of participants. Additionally, we demonstrated that patient-specific field-cable models could predict retinal activity and phosphene size. These computational models could be beneficial for determining optimal stimulation settings in silico, circumventing the trial-and-error testing of a large parameter space in clinic.
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Affiliation(s)
- Kathleen E Kish
- Biomedical Engineering, University of Michigan, Ann Arbor, 48105, USA
- BioInterfaces Institute, University of Michigan, Ann Arbor, 48105, USA
| | - Alex Yuan
- Ophthalmology and Ophthalmic Research, Cole Eye Institute, Cleveland Clinic Foundation, Cleveland, 44195, USA
| | - James D Weiland
- Biomedical Engineering, University of Michigan, Ann Arbor, 48105, USA.
- BioInterfaces Institute, University of Michigan, Ann Arbor, 48105, USA.
- Ophthalmology and Visual Science, University of Michigan, Ann Arbor, 48105, USA.
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Granley J, Fauvel T, Chalk M, Beyeler M. Human-in-the-Loop Optimization for Deep Stimulus Encoding in Visual Prostheses. ADVANCES IN NEURAL INFORMATION PROCESSING SYSTEMS 2023; 36:79376-79398. [PMID: 38984104 PMCID: PMC11232484] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Subscribe] [Scholar Register] [Indexed: 07/11/2024]
Abstract
Neuroprostheses show potential in restoring lost sensory function and enhancing human capabilities, but the sensations produced by current devices often seem unnatural or distorted. Exact placement of implants and differences in individual perception lead to significant variations in stimulus response, making personalized stimulus optimization a key challenge. Bayesian optimization could be used to optimize patient-specific stimulation parameters with limited noisy observations, but is not feasible for high-dimensional stimuli. Alternatively, deep learning models can optimize stimulus encoding strategies, but typically assume perfect knowledge of patient-specific variations. Here we propose a novel, practically feasible approach that overcomes both of these fundamental limitations. First, a deep encoder network is trained to produce optimal stimuli for any individual patient by inverting a forward model mapping electrical stimuli to visual percepts. Second, a preferential Bayesian optimization strategy utilizes this encoder to optimize patient-specific parameters for a new patient, using a minimal number of pairwise comparisons between candidate stimuli. We demonstrate the viability of this approach on a novel, state-of-the-art visual prosthesis model. We show that our approach quickly learns a personalized stimulus encoder, leads to dramatic improvements in the quality of restored vision, and is robust to noisy patient feedback and misspecifications in the underlying forward model. Overall, our results suggest that combining the strengths of deep learning and Bayesian optimization could significantly improve the perceptual experience of patients fitted with visual prostheses and may prove a viable solution for a range of neuroprosthetic technologies.
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Affiliation(s)
- Jacob Granley
- Department of Computer Science, University of California, Santa Barbara
| | - Tristan Fauvel
- Institut de la Vision, Sorbonne Université, 17 rue Moreau, F-75012 Paris, France, Now with Quinten Health
| | - Matthew Chalk
- Institut de la Vision, Sorbonne Université, 17 rue Moreau, F-75012 Paris, France
| | - Michael Beyeler
- Department of Computer Science, Department of Psychological & Brain Sciences, University of California, Santa Barbara
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Kerschensteiner D. Losing, preserving, and restoring vision from neurodegeneration in the eye. Curr Biol 2023; 33:R1019-R1036. [PMID: 37816323 PMCID: PMC10575673 DOI: 10.1016/j.cub.2023.08.044] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/12/2023]
Abstract
The retina is a part of the brain that sits at the back of the eye, looking out onto the world. The first neurons of the retina are the rod and cone photoreceptors, which convert changes in photon flux into electrical signals that are the basis of vision. Rods and cones are frequent targets of heritable neurodegenerative diseases that cause visual impairment, including blindness, in millions of people worldwide. This review summarizes the diverse genetic causes of inherited retinal degenerations (IRDs) and their convergence onto common pathogenic mechanisms of vision loss. Currently, there are few effective treatments for IRDs, but recent advances in disparate areas of biology and technology (e.g., genome editing, viral engineering, 3D organoids, optogenetics, semiconductor arrays) discussed here enable promising efforts to preserve and restore vision in IRD patients with implications for neurodegeneration in less approachable brain areas.
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Affiliation(s)
- Daniel Kerschensteiner
- Department of Ophthalmology and Visual Sciences, Washington University School of Medicine, St. Louis, MO 63110, USA; Department of Neuroscience, Washington University School of Medicine, St. Louis, MO 63110, USA; Department of Biomedical Engineering, Washington University School of Medicine, St. Louis, MO 63110, USA.
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10
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Kish KE, Yuan A, Weiland JD. Patient-specific computational models of retinal prostheses. RESEARCH SQUARE 2023:rs.3.rs-3168193. [PMID: 37577674 PMCID: PMC10418526 DOI: 10.21203/rs.3.rs-3168193/v1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 08/15/2023]
Abstract
Retinal prostheses stimulate inner retinal neurons to create visual perception for blind patients. Implanted arrays have many small electrodes, which act as pixels. Not all electrodes induce perception at the same stimulus amplitude, requiring clinicians to manually establish a visual perception threshold for each one. Phosphenes created by single-electrode stimuli can also vary in shape, size, and brightness. Computational models provide a tool to predict inter-electrode variability and automate device programming. In this study, we created statistical and patient-specific field-cable models to investigate inter-electrode variability across seven epiretinal prosthesis users. Our statistical analysis revealed that retinal thickness beneath the electrode correlated with perceptual threshold, with a significant fixed effect across participants. Electrode-retina distance and electrode impedance also correlated with perceptual threshold for some participants, but these effects varied by individual. We developed a novel method to construct patient-specific field-cable models from optical coherence tomography images. Predictions with these models significantly correlated with perceptual threshold for 80% of participants. Additionally, we demonstrated that patient-specific field-cable models could predict retinal activity and phosphene size. These computational models could be beneficial for determining optimal stimulation settings in silico, circumventing the trial-and-error testing of a large parameter space in clinic.
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Affiliation(s)
| | - Alex Yuan
- Cole Eye Institute, Cleveland Clinic Foundation
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11
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Palanker D. Electronic Retinal Prostheses. Cold Spring Harb Perspect Med 2023; 13:a041525. [PMID: 36781222 PMCID: PMC10411866 DOI: 10.1101/cshperspect.a041525] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/15/2023]
Abstract
Retinal prostheses are a promising means for restoring sight to patients blinded by photoreceptor atrophy. They introduce visual information by electrical stimulation of the surviving inner retinal neurons. Subretinal implants target the graded-response secondary neurons, primarily the bipolar cells, which then transfer the information to the ganglion cells via the retinal neural network. Therefore, many features of natural retinal signal processing can be preserved in this approach if the inner retinal network is retained. Epiretinal implants stimulate primarily the ganglion cells, and hence should encode the visual information in spiking patterns, which, ideally, should match the target cell types. Currently, subretinal arrays are being developed primarily for restoration of central vision in patients impaired by age-related macular degeneration (AMD), while epiretinal implants-for patients blinded by retinitis pigmentosa, where the inner retina is less preserved. This review describes the concepts and technologies, preclinical characterization of prosthetic vision and clinical outcomes, and provides a glimpse into future developments.
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Affiliation(s)
- Daniel Palanker
- Department of Ophthalmology and Hansen Experimental Physics Laboratory, Stanford University, Stanford, California 94305, USA
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12
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Fine I, Boynton GM. Pulse trains to percepts: A virtual patient describing the perceptual effects of human visual cortical stimulation. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.03.18.532424. [PMID: 36993519 PMCID: PMC10055195 DOI: 10.1101/2023.03.18.532424] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/19/2023]
Abstract
The field of cortical sight restoration prostheses is making rapid progress with three clinical trials of visual cortical prostheses underway. However, as yet, we have only limited insight into the perceptual experiences produced by these implants. Here we describe a computational model or 'virtual patient', based on the neurophysiological architecture of V1, which successfully predicts the perceptual experience of participants across a wide range of previously published cortical stimulation studies describing the location, size, brightness and spatiotemporal shape of electrically induced percepts in humans. Our simulations suggest that, in the foreseeable future the perceptual quality of cortical prosthetic devices is likely to be limited by the neurophysiological organization of visual cortex, rather than engineering constraints.
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13
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Wang C, Fang C, Zou Y, Yang J, Sawan M. Artificial intelligence techniques for retinal prostheses: a comprehensive review and future direction. J Neural Eng 2023; 20. [PMID: 36634357 DOI: 10.1088/1741-2552/acb295] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2022] [Accepted: 01/12/2023] [Indexed: 01/14/2023]
Abstract
Objective. Retinal prostheses are promising devices to restore vision for patients with severe age-related macular degeneration or retinitis pigmentosa disease. The visual processing mechanism embodied in retinal prostheses play an important role in the restoration effect. Its performance depends on our understanding of the retina's working mechanism and the evolvement of computer vision models. Recently, remarkable progress has been made in the field of processing algorithm for retinal prostheses where the new discovery of the retina's working principle and state-of-the-arts computer vision models are combined together.Approach. We investigated the related research on artificial intelligence techniques for retinal prostheses. The processing algorithm in these studies could be attributed to three types: computer vision-related methods, biophysical models, and deep learning models.Main results. In this review, we first illustrate the structure and function of the normal and degenerated retina, then demonstrate the vision rehabilitation mechanism of three representative retinal prostheses. It is necessary to summarize the computational frameworks abstracted from the normal retina. In addition, the development and feature of three types of different processing algorithms are summarized. Finally, we analyze the bottleneck in existing algorithms and propose our prospect about the future directions to improve the restoration effect.Significance. This review systematically summarizes existing processing models for predicting the response of the retina to external stimuli. What's more, the suggestions for future direction may inspire researchers in this field to design better algorithms for retinal prostheses.
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Affiliation(s)
- Chuanqing Wang
- Center of Excellence in Biomedical Research on Advanced Integrated-on-chips Neurotechnologies, School of Engineering, Westlake University, Hangzhou 310030, People's Republic of China
| | - Chaoming Fang
- Center of Excellence in Biomedical Research on Advanced Integrated-on-chips Neurotechnologies, School of Engineering, Westlake University, Hangzhou 310030, People's Republic of China
| | - Yong Zou
- Beijing Institute of Radiation Medicine, Beijing, People's Republic of China
| | - Jie Yang
- Center of Excellence in Biomedical Research on Advanced Integrated-on-chips Neurotechnologies, School of Engineering, Westlake University, Hangzhou 310030, People's Republic of China
| | - Mohamad Sawan
- Center of Excellence in Biomedical Research on Advanced Integrated-on-chips Neurotechnologies, School of Engineering, Westlake University, Hangzhou 310030, People's Republic of China
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14
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Roh H, Otgondemberel Y, Im M. Short pulses of epiretinal prostheses evoke network-mediated responses in retinal ganglion cells by stimulating presynaptic neurons. J Neural Eng 2022; 19. [PMID: 36055185 DOI: 10.1088/1741-2552/ac8ed7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2022] [Accepted: 09/02/2022] [Indexed: 11/12/2022]
Abstract
OBJECTIVE Microelectronic retinal implant aims to restore functional vision with electric stimulation. Short pulses are generally known to directly activate retinal ganglion cells (RGCs) with a notion of one or two spike(s) per pulse. In the present work, we systematically explore network-mediated responses that arise from various short pulses in both normal and degenerate retinas. APPROACH Cell-attached patch clamping was used to record spiking responses of RGCs in wild-type (C57BL/6J) and retinal degeneration (rd10) mice. Alpha RGCs of the mouse retinas were targeted by their large soma sizes and classified by their responses to spot flashes. Then, RGCs were electrically stimulated by various conditions such as duration (100-460 μs), count (1-10), amplitude (100-400 μA), and repeating frequency (10-40 Hz) of short pulses. Also, their responses were compared with each own response to a single 4-ms-long pulse which is known to evoke strong indirect responses. MAIN RESULTS Short pulses evoked strong network-mediated responses not only in both ON and OFF types of RGCs in the healthy retinas but also in RGCs of the severely degenerate retina. However, the spike timing consistency across repeats not decreased significantly in the rd10 RGCs compared to the healthy ON and OFF RGCs. Network-mediated responses of ON RGCs were highly dependent on the current amplitude of stimuli but much less on the pulse count and the repetition frequency. In contrast, responses of OFF RGCs were more influenced by the number of stimuli than the current amplitude. SIGNIFICANCE Our results demonstrate that short pulses also elicit indirect responses by activating presynaptic neurons. In the case of the commercial retinal prostheses using repeating short pulses, there is a possibility that the performance of clinical devices is highly related to the preserved retinal circuits. Therefore, examination of surviving retinal neurons in patients would be necessary to improve the efficacy of retinal prostheses.
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Affiliation(s)
- Hyeonhee Roh
- Korea Institute of Science and Technology (KIST), 5 Hwarang-ro 14-gil, Seongbuk-gu, Seoul, 02792, Korea (the Republic of)
| | - Yanjinsuren Otgondemberel
- Brain Science Institute, Korea Institute of Science and Technology (KIST), 5 Hwarang-ro 14-gil, Seongbuk-gu, Seoul, 02792, Korea (the Republic of)
| | - Maesoon Im
- Brain Science Institute, Center for BioMicrosystems, Korea Institute of Science and Technology, 5 Hwarang-ro 14-gil, Seongbuk-gu, L7325B, Seoul, Seoul, Seoul, 02792, Korea (the Republic of)
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15
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Yücel EI, Sadeghi R, Kartha A, Montezuma SR, Dagnelie G, Rokem A, Boynton GM, Fine I, Beyeler M. Factors affecting two-point discrimination in Argus II patients. Front Neurosci 2022; 16:901337. [PMID: 36090266 PMCID: PMC9448992 DOI: 10.3389/fnins.2022.901337] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2022] [Accepted: 07/11/2022] [Indexed: 11/13/2022] Open
Abstract
Two of the main obstacles to the development of epiretinal prosthesis technology are electrodes that require current amplitudes above safety limits to reliably elicit percepts, and a failure to consistently elicit pattern vision. Here, we explored the causes of high current amplitude thresholds and poor spatial resolution within the Argus II epiretinal implant. We measured current amplitude thresholds and two-point discrimination (the ability to determine whether one or two electrodes had been stimulated) in 3 blind participants implanted with Argus II devices. Our data and simulations show that axonal stimulation, lift and retinal damage all play a role in reducing performance in the Argus 2, by either limiting sensitivity and/or reducing spatial resolution. Understanding the relative role of these various factors will be critical for developing and surgically implanting devices that can successfully subserve pattern vision.
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Affiliation(s)
- Ezgi I. Yücel
- Department of Psychology, University of Washington, Seattle, WA, United States
| | - Roksana Sadeghi
- Department of Biomedical Engineering, Johns Hopkins School of Medicine, Baltimore, MD, United States
| | - Arathy Kartha
- Department of Ophthalmology, Johns Hopkins School of Medicine, Baltimore, MD, United States
| | - Sandra Rocio Montezuma
- Department of Ophthalmology and Visual Neurosciences, University of Minnesota, Minneapolis, MN, United States
| | - Gislin Dagnelie
- Department of Ophthalmology, Johns Hopkins School of Medicine, Baltimore, MD, United States
| | - Ariel Rokem
- Department of Psychology, University of Washington, Seattle, WA, United States,eScience Institute, University of Washington, Seattle, WA, United States
| | - Geoffrey M. Boynton
- Department of Psychology, University of Washington, Seattle, WA, United States
| | - Ione Fine
- Department of Psychology, University of Washington, Seattle, WA, United States,*Correspondence: Ione Fine,
| | - Michael Beyeler
- Department of Computer Science, University of California, Santa Barbara, Santa Barbara, CA, United States,Department of Psychological and Brain Sciences, University of California, Santa Barbara, Santa Barbara, CA, United States
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16
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Jung R, Kelbsch C, Wilhelm H, Wilhelm B, Strasser T, Peters T, Kempf M, Kortüm F, Pohl L, Stingl K, Stingl K. Cell-specific electrical stimulation of human retinal neurons assessed by pupillary response dynamics in vivo. Exp Eye Res 2022; 222:109185. [PMID: 35850172 DOI: 10.1016/j.exer.2022.109185] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2022] [Revised: 06/12/2022] [Accepted: 07/05/2022] [Indexed: 11/30/2022]
Abstract
Studies on the electrical excitability of retinal neurons show that photoreceptors and other cell types can be selectively activated by distinct stimulation frequencies in vitro. Yet, this principle still needs to be validated in humans in vivo. As a first step, this study explored the frequency preferences of human rods by means of transcorneal electrostimulation (TES), using the electrically-elicited pupillary responses (EEPRs) as an objective readout. The stimulation paradigm contained a 1.2 Hz sinusoidal envelope, which was superimposed on variable carrier frequencies (4-30 Hz). These currents were delivered to one of the participant's eyes via a corneal electrode and consensual pupillary reactions were recorded from the contralateral eye. The responsiveness of the retina at each frequency was assessed based on the EEPR dynamics. Differences between healthy participants and patients with retinitis pigmentosa were evaluated to identify the preferred frequency range of rods. The responsiveness of healthy individuals revealed a clear peak around 6-8 Hz. In contrast, the pupillary responses of patients were significantly reduced in the lower frequency range. These findings suggest that the responses in this frequency bin were selectively mediated by rods. This work provides evidence that different retinal cell types can be selectively activated via TES in vivo, and that this effect can be captured noninvasively using EEPRs. This knowledge may be exploited for the diagnostics and therapy of retinal diseases, e.g., to design cell-specific functional tests for the degenerating retina, or to optimize stimulation paradigms which are currently used by retinal prostheses.
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Affiliation(s)
- Ronja Jung
- University Eye Hospital, Center for Ophthalmology, University of Tuebingen, 72076, Tuebingen, Germany.
| | - Carina Kelbsch
- University Eye Hospital, Center for Ophthalmology, University of Tuebingen, 72076, Tuebingen, Germany; Pupil Research Group, Center for Ophthalmology, University of Tuebingen, 72076, Tuebingen, Germany
| | - Helmut Wilhelm
- Pupil Research Group, Center for Ophthalmology, University of Tuebingen, 72076, Tuebingen, Germany
| | - Barbara Wilhelm
- Pupil Research Group, Center for Ophthalmology, University of Tuebingen, 72076, Tuebingen, Germany
| | - Torsten Strasser
- University Eye Hospital, Center for Ophthalmology, University of Tuebingen, 72076, Tuebingen, Germany; Pupil Research Group, Center for Ophthalmology, University of Tuebingen, 72076, Tuebingen, Germany; Institute for Ophthalmic Research, University of Tübingen, 72076, Tübingen, Germany
| | - Tobias Peters
- Pupil Research Group, Center for Ophthalmology, University of Tuebingen, 72076, Tuebingen, Germany
| | - Melanie Kempf
- University Eye Hospital, Center for Ophthalmology, University of Tuebingen, 72076, Tuebingen, Germany; Center for Rare Diseases, University of Tübingen, 72076, Tübingen, Germany
| | - Friederike Kortüm
- University Eye Hospital, Center for Ophthalmology, University of Tuebingen, 72076, Tuebingen, Germany
| | - Lisa Pohl
- University Eye Hospital, Center for Ophthalmology, University of Tuebingen, 72076, Tuebingen, Germany
| | - Krunoslav Stingl
- University Eye Hospital, Center for Ophthalmology, University of Tuebingen, 72076, Tuebingen, Germany; Pupil Research Group, Center for Ophthalmology, University of Tuebingen, 72076, Tuebingen, Germany; Center for Rare Diseases, University of Tübingen, 72076, Tübingen, Germany
| | - Katarina Stingl
- University Eye Hospital, Center for Ophthalmology, University of Tuebingen, 72076, Tuebingen, Germany; Center for Rare Diseases, University of Tübingen, 72076, Tübingen, Germany
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17
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Flexible ultrasound-induced retinal stimulating piezo-arrays for biomimetic visual prostheses. Nat Commun 2022; 13:3853. [PMID: 35788594 PMCID: PMC9253314 DOI: 10.1038/s41467-022-31599-4] [Citation(s) in RCA: 31] [Impact Index Per Article: 15.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2021] [Accepted: 06/22/2022] [Indexed: 12/29/2022] Open
Abstract
Electronic visual prostheses, or biomimetic eyes, have shown the feasibility of restoring functional vision in the blind through electrical pulses to initiate neural responses artificially. However, existing visual prostheses predominantly use wired connections or electromagnetic waves for powering and data telemetry, which raises safety concerns or couples inefficiently to miniaturized implant units. Here, we present a flexible ultrasound-induced retinal stimulating piezo-array that can offer an alternative wireless artificial retinal prosthesis approach for evoking visual percepts in blind individuals. The device integrates a two-dimensional piezo-array with 32-pixel stimulating electrodes in a flexible printed circuit board. Each piezo-element can be ultrasonically and individually activated, thus, spatially reconfigurable electronic patterns can be dynamically applied via programmable ultrasound beamlines. As a proof of concept, we demonstrate the ultrasound-induced pattern reconstruction in ex vivo murine retinal tissue, showing the potential of this approach to restore functional, life-enhancing vision in people living with blindness.
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18
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Fauvel T, Chalk M. Human-in-the-loop optimization of visual prosthetic stimulation. J Neural Eng 2022; 19. [PMID: 35667363 DOI: 10.1088/1741-2552/ac7615] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2022] [Accepted: 06/06/2022] [Indexed: 11/12/2022]
Abstract
Retinal prostheses are a promising strategy to restore sight to patients with retinal degenerative diseases. These devices compensate for the loss of photoreceptors by electrically stimulating neurons in the retina. Currently, the visual function that can be recovered with such devices is very limited. This is due, in part, to current spread, unintended axonal activation, and the limited resolution of existing devices. Here we show, using a recent model of prosthetic vision, that optimizing how visual stimuli are encoded by the device can help overcome some of these limitations, leading to dramatic improvements in visual perception. APPROACH We propose a strategy to do this in practice, using patients' feedback in a visual task. The main challenge of our approach comes from the fact that, typically, one only has access to a limited number of noisy responses from patients. We propose two ways to deal with this: first, we use a model of prosthetic vision to constrain and simplify the optimization. We show that, if one knew the parameters of this model for a given patient, it would be possible to greatly improve their perceptual performance. Second we propose a preferential Bayesian optimization to efficiently learn these model parameters for each patient, using minimal trials. MAIN RESULTS To test our approach, we presented healthy subjects with visual stimuli generated by a recent model of prosthetic vision, to replicate the perceptual experience of patients fitted with an implant. Our optimization procedure led to significant and robust improvements in perceived image quality, that transferred to increased performance in other tasks. SIGNIFICANCE Importantly, our strategy is agnostic to the type of prosthesis and thus could readily be implemented in existing implants.
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Affiliation(s)
- Tristan Fauvel
- Institut de la Vision, INSERM, 17 Rue Moreau, Paris, Île-de-France, 75014, FRANCE
| | - Matthew Chalk
- Institut de l a Vision, INSERM, 17 Rue Moreau, Paris, 75014, FRANCE
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19
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Van Gelder RN, Chiang MF, Dyer MA, Greenwell TN, Levin LA, Wong RO, Svendsen CN. Regenerative and restorative medicine for eye disease. Nat Med 2022; 28:1149-1156. [PMID: 35715505 PMCID: PMC10718186 DOI: 10.1038/s41591-022-01862-8] [Citation(s) in RCA: 29] [Impact Index Per Article: 14.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2022] [Accepted: 05/06/2022] [Indexed: 12/11/2022]
Abstract
Causes of blindness differ across the globe; in higher-income countries, most blindness results from the degeneration of specific classes of cells in the retina, including retinal pigment epithelium (RPE), photoreceptors, and retinal ganglion cells. Advances over the past decade in retinal regenerative medicine have allowed each of these cell types to be produced ex vivo from progenitor stem cells. Here, we review progress in applying these technologies to cell replacement - with the goal of vision restoration in degenerative disease. We discuss the landscape of human clinical trials for RPE transplantation and advanced preclinical studies for other cell types. We also review progress toward in situ repair of retinal degeneration using endogenous progenitor cells. Finally, we provide a high-level overview of progress toward prosthetic ocular vision restoration, including advanced photovoltaic devices, opsin-based gene therapy, and small-molecule photoswitches. Progress in each of these domains is at or near the human clinical-trial stage, bringing the audacious goal of vision restoration within sight.
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Affiliation(s)
- Russell N Van Gelder
- Karalis-Johnson Retina Center, Department of Ophthalmology, University of Washington School of Medicine, Seattle, WA, USA.
- Department of Biological Structure, University of Washington School of Medicine, Seattle, WA, USA.
- Department of Pathology and Laboratory Medicine, University of Washington School of Medicine, Seattle, WA, USA.
- Roger and Angie Karalis Johnson Retina Center, University of Washington School of Medicine, Seattle, WA, USA.
| | - Michael F Chiang
- National Eye Institute, National Institutes of Health, Bethesda, MD, USA
| | - Michael A Dyer
- Department of Developmental Neurobiology, St. Jude's Research Hospital, Memphis, TN, USA
| | - Thomas N Greenwell
- National Eye Institute, National Institutes of Health, Bethesda, MD, USA
| | - Leonard A Levin
- Department of Ophthalmology and Visual Sciences, McGill University, Montreal, Quebec, Canada
- Department of Neurology & Neurosurgery, McGill University, Montreal, Quebec, Canada
| | - Rachel O Wong
- Karalis-Johnson Retina Center, Department of Ophthalmology, University of Washington School of Medicine, Seattle, WA, USA
- Department of Biological Structure, University of Washington School of Medicine, Seattle, WA, USA
| | - Clive N Svendsen
- Board of Governors Regenerative Medicine Institute, Los Angeles, CA, USA
- Department of Biomedical Sciences, Cedars Sinai Medical Center, Los Angeles, CA, USA
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20
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Christie B, Sadeghi R, Kartha A, Caspi A, Tenore FV, Klatzky RL, Dagnelie G, Billings S. Sequential epiretinal stimulation improves discrimination in simple shape discrimination tasks only. J Neural Eng 2022; 19. [PMID: 35613043 DOI: 10.1088/1741-2552/ac7326] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/2022] [Accepted: 05/24/2022] [Indexed: 11/12/2022]
Abstract
OBJECTIVE Electrical stimulation of the retina can elicit flashes of light called phosphenes, which can be used to restore rudimentary vision for people with blindness. Functional sight requires stimulation of multiple electrodes to create patterned vision, but phosphenes tend to merge together in an uninterpretable way. Sequentially stimulating electrodes in human visual cortex has recently demonstrated that shapes could be "drawn" with better perceptual resolution relative to simultaneous stimulation. The goal of this study was to evaluate if sequential stimulation would also form clearer shapes when the retina is the neural target. APPROACH Two human participants with retinitis pigmentosa who had Argus® II retinal prostheses participated in this study. We evaluated different temporal parameters for sequential stimulation in phosphene shape mapping and forced-choice discrimination tasks. For the discrimination tasks, performance was compared between stimulating electrodes simultaneously versus sequentially. MAIN RESULTS Phosphenes elicited by different electrodes were reported as vastly different shapes. Sequential electrode stimulation outperformed simultaneous stimulation in simple discrimination tasks, in which shapes were created by stimulating 3-4 electrodes, but not in more complex discrimination tasks involving 5+ electrodes. For sequential stimulation, the optimal pulse train duration was 200 ms when stimulating at 20 Hz and the optimal gap interval was tied between 0 and 50 ms. Efficacy of sequential stimulation also depended strongly on selecting electrodes that elicited phosphenes with similar shapes and sizes. SIGNIFICANCE An epiretinal prosthesis can produce coherent simple shapes with a sequential stimulation paradigm, which can be used as rudimentary visual feedback. However, success in creating more complex shapes, such as letters of the alphabet, is still limited. Sequential stimulation may be most beneficial for epiretinal prostheses in simple tasks, such as basic navigation, rather than complex tasks such as object identification.
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Affiliation(s)
- Breanne Christie
- Research and Exploratory Development Department, Johns Hopkins University Applied Physics Laboratory, 11100 Johns Hopkins Road, Laurel, Maryland, 20723, UNITED STATES
| | - Roksana Sadeghi
- Department of Biomedical Engineering, Johns Hopkins School of Medicine, 733 N Broadway, Baltimore, Maryland, 21205, UNITED STATES
| | - Arathy Kartha
- Department of Ophthalmology, Johns Hopkins School of Medicine, 1800 Orleans St., Baltimore, Maryland, 21287, UNITED STATES
| | - Avi Caspi
- Jerusalem College of Technology, Ha-Va'ad ha-Le'umi St 21, Jerusalem, 91160, ISRAEL
| | - Francesco V Tenore
- Research and Exploratory Development Department, Johns Hopkins University Applied Physics Laboratory, 11100 Johns Hopkins Road, Laurel, Maryland, 20723, UNITED STATES
| | - Roberta L Klatzky
- Department of Psychology, Carnegie Mellon University, 5000 Forbes Ave, Pittsburgh, Pennsylvania, 15213-3815, UNITED STATES
| | - Gislin Dagnelie
- Department of Ophthalmology, Johns Hopkins School of Medicine, 1800 Orleans St., Baltimore, Maryland, 21287, UNITED STATES
| | - Seth Billings
- Research and Exploratory Development Department, Johns Hopkins University Applied Physics Laboratory, 11100 Johns Hopkins Road, Laurel, Maryland, 20723-6005, UNITED STATES
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21
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Italiano ML, Guo T, Lovell NH, Tsai D. Improving the spatial resolution of artificial vision using midget retinal ganglion cell populations modelled at the human fovea. J Neural Eng 2022; 19. [PMID: 35609556 DOI: 10.1088/1741-2552/ac72c2] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2022] [Accepted: 05/24/2022] [Indexed: 11/11/2022]
Abstract
OBJECTIVE Retinal prostheses seek to create artificial vision by stimulating surviving retinal neurons of patients with profound vision impairment. Notwithstanding tremendous research efforts, the performance of all implants tested to date has remained rudimentary, incapable of overcoming the threshold for legal blindness. To maximize the perceptual efficacy of retinal prostheses, a device must be capable of controlling retinal neurons with greater spatiotemporal precision. Most studies of retinal stimulation were derived from either non-primate species or the peripheral primate retina. We investigated if artificial stimulation could leverage the high spatial resolution afforded by the neural substrates at the primate fovea and surrounding regions to achieve improved percept qualities. APPROACH We began by developing a new computational model capable of generating anatomically accurate retinal ganglion cell (RGC) populations within the human central retina. Next, multiple RGC populations across the central retina were stimulated in-silico to compare clinical and recently proposed neurostimulation configurations based on their ability to improve perceptual efficacy and reduce activation thresholds. MAIN RESULTS Our model uniquely upholds eccentricity-dependent characteristics such as RGC density and dendritic field diameter, whilst incorporating anatomically accurate features such as axon projection and three-dimensional RGC layering, features often forgone in favor of reduced computational complexity. Following epiretinal stimulation, the RGCs in our model produced response patterns in shapes akin to the complex percepts reported in clinical trials. Our results also demonstrated that even within the neuron-dense central retina, epiretinal stimulation using a multi-return hexapolar electrode arrangement could reliably achieve spatially focused RGC activation and could achieve single-cell excitation in 74% of all tested locations. SIGNIFICANCE This study establishes an anatomically accurate three-dimensional model of the human central retina and demonstrates the potential for an epiretinal hexapolar configuration to achieve consistent, spatially confined retinal responses, even within the neuron-dense foveal region. Our results promote the prospect and optimization of higher spatial resolution in future epiretinal implants.
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Affiliation(s)
- Michael Lewis Italiano
- Graduate School of Biomedical Engineering, University of New South Wales, Sydney, Sydney, New South Wales, 2052, AUSTRALIA
| | - Tianruo Guo
- Graduate School of Biomedical Engineering, University of New South Wales, Sydney, Sydney, New South Wales, 2052, AUSTRALIA
| | - Nigel H Lovell
- Graduate School of Biomedical Engineering, University of New South Wales, Sydney, Sydney, New South Wales, 2052, AUSTRALIA
| | - David Tsai
- Graduate School of Biomedical Engineering, University of New South Wales, Sydney, Sydney, New South Wales, 2052, AUSTRALIA
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22
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Avraham D, Yitzhaky Y. Simulating the perceptual effects of electrode-retina distance in prosthetic vision. J Neural Eng 2022; 19. [PMID: 35561665 DOI: 10.1088/1741-2552/ac6f82] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2022] [Accepted: 05/13/2022] [Indexed: 11/12/2022]
Abstract
OBJECTIVE Retinal prostheses aim to restore some vision in retinitis pigmentosa and age-related macular degeneration blind patients. Many spatial and temporal aspects have been found to affect prosthetic vision. Our objective is to study the impact of the space-variant distance between the stimulating electrodes and the surface of the retina on prosthetic vision and how to mitigate this impact. APPROACH A prosthetic vision simulation was built to demonstrate the perceptual effects of the electrode-retina distance (ERD) with different random spatial variations, such as size, brightness, shape, dropout, and spatial shifts. Three approaches for reducing the ERD effects are demonstrated: electrode grouping (quads), ERD-based input-image enhancement, and object scanning with and without phosphene persistence. A quantitative assessment for the first two approaches was done based on experiments with 20 subjects and three vision-based computational image similarity metrics. MAIN RESULTS The effects of various ERDs on phosphenes' size, brightness, and shape were simulated. Quads, chosen according to the ERDs, effectively elicit phosphenes without exceeding the safe charge density limit, whereas single electrodes with large ERD cannot do so. Input-image enhancement reduced the ERD effects effectively. These two approaches significantly improved ERD-affected prosthetic vision according to the experiment and image similarity metrics. A further reduction of the ERD effects was achieved by scanning an object while moving the head. SIGNIFICANCE ERD has multiple effects on perception with retinal prostheses. One of them is vision loss caused by the incapability of electrodes with large ERD to evoke phosphenes. The three approaches presented in this study can be used separately or together to mitigate the impact of ERD. A consideration of our approaches in reducing the perceptual effects of the ERD may help improve the perception with current prosthetic technology and influence the design of future prostheses.
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Affiliation(s)
- David Avraham
- Department of Electro-Optical Engineering, Ben-Gurion University of the Negev, 1 Ben-Gurion Blvd., Beer-Sheva, 84105, ISRAEL
| | - Yitzhak Yitzhaky
- Electro-Optical Engineering, School of Engineering, Ben-Gurion University of the Negev, 1 Ben-Gurion Blvd., Beer-Sheva, Southern, 84105, ISRAEL
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23
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Song X, Qiu S, Shivdasani MN, Zhou F, Liu Z, Ma S, Chai X, Chen Y, Cai X, Guo T, Li L. An in-silico analysis of electrically-evoked responses of midget and parasol retinal ganglion cells in different retinal regions. J Neural Eng 2022; 19. [PMID: 35255486 DOI: 10.1088/1741-2552/ac5b18] [Citation(s) in RCA: 11] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2021] [Accepted: 03/07/2022] [Indexed: 11/12/2022]
Abstract
BACKGROUND Visual outcomes provided by present retinal prostheses that primarily target retinal ganglion cells (RGCs) through epiretinal stimulation remain rudimentary, partly due to the limited knowledge of retinal responses under electrical stimulation. Better understanding of how different retinal regions can be quantitatively controlled with high spatial accuracy, will be beneficial to the design of micro-electrode arrays (MEAs) and stimulation strategies for next-generation wide-view, high-resolution epiretinal implants. METHODS A computational model was developed to assess neural activity at different eccentricities (2 mm and 5 mm) within the human retina. This model included midget and parasol RGCs with anatomically accurate cell distribution and cell-specific morphological information. We then performed in silico investigations of region-specific RGC responses to epiretinal electrical stimulation using varied electrode sizes (5 µm - 210 µm diameter), emulating both commercialized retinal implants and recently-developed prototype devices. RESULTS Our model of epiretinal stimulation predicted RGC population excitation analogous to the complex percepts reported in human subjects. Following this, our simulations suggest that midget and parasol RGCs have characteristic regional differences in excitation under preferred electrode sizes. Relatively central (2 mm) regions demonstrated higher number of excited RGCs but lower overall activated receptive field (RF) areas under the same stimulus amplitudes (two-way ANOVA, p < 0.05). Furthermore, the activated RGC numbers per unit active RF area (number-RF ratio) were significantly higher in central than in peripheral regions, and higher in the midget than in the parasol population under all tested electrode sizes (two-way ANOVA, p < 0.05). Our simulations also suggested that smaller electrodes exhibit a higher range of controllable stimulation parameters to achieve pre-defined performance of RGC excitation. ..
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Affiliation(s)
- Xiaoyu Song
- , Shanghai Jiao Tong University, Dongchuan Road, Shanghai Minhang District No. 800, Shanghai, 200240, CHINA
| | - Shirong Qiu
- Shanghai Jiao Tong University, Dongchuan Road, Shanghai Minhang District No. 800, Shanghai, 200240, CHINA
| | - Mohit N Shivdasani
- Graduate School of Biomedical Engineering, University of New South Wales, Lower Ground, Samuels Building (F25), Kensington, New South Wales, 2052, AUSTRALIA
| | - Feng Zhou
- Shanghai Jiao Tong University, Dongchuan Road, Shanghai Minhang District No. 800, Shanghai, 200240, CHINA
| | - Zhengyang Liu
- Shanghai Jiao Tong University, Dongchuan Road, Shanghai Minhang District No. 800, Shanghai, 200240, CHINA
| | - Saidong Ma
- Shanghai Jiao Tong University, Dongchuan Road, Shanghai Minhang District No. 800, Shanghai, 200240, CHINA
| | - Xinyu Chai
- School of Biomedical Engineering, Shanghai Jiao Tong University, Shanghai 200240, Shanghai, 200240, CHINA
| | - Yao Chen
- Department of Biomedical Engineering, Shanghai Jiao Tong University, Shanghai 200040, Shanghai, 200240, CHINA
| | - Xuan Cai
- Department of Ophthalmology, Shanghai Jiao Tong University Affiliated Sixth People's Hospital, 600 Yishan Road, Shanghai, Shanghai, 200233, CHINA
| | - Tianruo Guo
- the University of New South Wales, Lower Ground, Samuels Building (F25), Sydney, 2052, AUSTRALIA
| | - Liming Li
- Shanghai Jiao Tong University, Dongchuan Road, Shanghai Minhang District No. 800, Shanghai, 200240, CHINA
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24
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Kasowski J, Beyeler M. Immersive Virtual Reality Simulations of Bionic Vision. AUGMENTED HUMANS 2022 2022; 2022:82-93. [PMID: 35856703 PMCID: PMC9289996 DOI: 10.1145/3519391.3522752] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/21/2023]
Abstract
Bionic vision uses neuroprostheses to restore useful vision to people living with incurable blindness. However, a major outstanding challenge is predicting what people "see" when they use their devices. The limited field of view of current devices necessitates head movements to scan the scene, which is difficult to simulate on a computer screen. In addition, many computational models of bionic vision lack biological realism. To address these challenges, we present VR-SPV, an open-source virtual reality toolbox for simulated prosthetic vision that uses a psychophysically validated computational model to allow sighted participants to "see through the eyes" of a bionic eye user. To demonstrate its utility, we systematically evaluated how clinically reported visual distortions affect performance in a letter recognition and an immersive obstacle avoidance task. Our results highlight the importance of using an appropriate phosphene model when predicting visual outcomes for bionic vision.
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Paknahad J, Humayun M, Lazzi G. Selective Activation of Retinal Ganglion Cell Subtypes Through Targeted Electrical Stimulation Parameters. IEEE Trans Neural Syst Rehabil Eng 2022; 30:350-359. [PMID: 35130164 PMCID: PMC8904155 DOI: 10.1109/tnsre.2022.3149967] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
To restore vision to the low vision, epiretinal implants have been developed to electrically stimulate the healthy retinal ganglion cells (RGCs) in the degenerate retina. Given the diversity of retinal ganglion cells as well as the difference in their visual function, selective activation of RGCs subtypes can significantly improve the quality of the restored vision. Our recent results demonstrated that with the proper modulation of the current amplitude, small D1-bistratified cells with the contribution to blue/yellow color opponent pathway can be selectively activated at high frequency (200 Hz). The computational results correlated with the clinical findings revealing the blue sensation of 5/7 subjects with epiretinal implants at high frequency. Here we further explored the impacts of alterations in pulse duration and interphase gap on the response of RGCs at high frequency. We used the developed RGCs, A2-monostratified and D1-bistratified, and examined their response to a range of pulse durations (0.1−1.2 ms) and interphase gaps (0−1 ms). We found that the use of short pulse durations with no interphase gap at high frequency increases the differential response of RGCs, offering better opportunities for selective activation of D1 cells. The presence of the interphase gap has shown to reduce the overall differential response of RGCs. We also explored how the low density of calcium channels enhances the responsiveness of RGCs at high frequency.
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Haji Ghaffari D, Akwaboah AD, Mirzakhalili E, Weiland JD. Real-Time Optimization of Retinal Ganglion Cell Spatial Activity in Response to Epiretinal Stimulation. IEEE Trans Neural Syst Rehabil Eng 2021; 29:2733-2741. [PMID: 34941514 PMCID: PMC8851408 DOI: 10.1109/tnsre.2021.3138297] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Retinal prostheses aim to improve visual perception in patients blinded by photoreceptor degeneration. However, shape and letter perception with these devices is currently limited due to low spatial resolution. Previous research has shown the retinal ganglion cell (RGC) spatial activity and phosphene shapes can vary due to the complexity of retina structure and electrode-retina interactions. Visual percepts elicited by single electrodes differ in size and shapes for different electrodes within the same subject, resulting in interference between phosphenes and an unclear image. Prior work has shown that better patient outcomes correlate with spatially separate phosphenes. In this study we use calcium imaging, in vitro retina, neural networks (NN), and an optimization algorithm to demonstrate a method to iteratively search for optimal stimulation parameters that create focal RGC activation. Our findings indicate that we can converge to stimulation parameters that result in focal RGC activation by sampling less than 1/3 of the parameter space. A similar process implemented clinically can reduce time required for optimizing implant operation and enable personalized fitting of retinal prostheses.
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Paknahad J, Kosta P, Bouteiller JMC, Humayun MS, Lazzi G. Mechanisms underlying activation of retinal bipolar cells through targeted electrical stimulation: a computational study. J Neural Eng 2021; 18. [PMID: 34826830 DOI: 10.1088/1741-2552/ac3dd8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2021] [Accepted: 11/26/2021] [Indexed: 11/12/2022]
Abstract
Objective. Retinal implants have been developed to electrically stimulate healthy retinal neurons in the progressively degenerated retina. Several stimulation approaches have been proposed to improve the visual percept induced in patients with retinal prostheses. We introduce a computational model capable of simulating the effects of electrical stimulation on retinal neurons. Leveraging this computational platform, we delve into the underlying mechanisms influencing the sensitivity of retinal neurons' response to various stimulus waveforms.Approach. We implemented a model of spiking bipolar cells (BCs) in the magnocellular pathway of the primate retina, diffuse BC subtypes (DB4), and utilized our multiscale admittance method (AM)-NEURON computational platform to characterize the response of BCs to epiretinal electrical stimulation with monophasic, symmetric, and asymmetric biphasic pulses.Main results. Our investigations yielded four notable results: (a) the latency of BCs increases as stimulation pulse duration lengthens; conversely, this latency decreases as the current amplitude increases. (b) Stimulation with a long anodic-first symmetric biphasic pulse (duration > 8 ms) results in a significant decrease in spiking threshold compared to stimulation with similar cathodic-first pulses (from 98.2 to 57.5µA). (c) The hyperpolarization-activated cyclic nucleotide-gated channel was a prominent contributor to the reduced threshold of BCs in response to long anodic-first stimulus pulses. (d) Finally, extending the study to asymmetric waveforms, our results predict a lower BCs threshold using asymmetric long anodic-first pulses compared to that of asymmetric short cathodic-first stimulation.Significance. This study predicts the effects of several stimulation parameters on spiking BCs response to electrical stimulation. Of importance, our findings shed light on mechanisms underlying the experimental observations from the literature, thus highlighting the capability of the methodology to predict and guide the development of electrical stimulation protocols to generate a desired biological response, thereby constituting an ideal testbed for the development of electroceutical devices.
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Affiliation(s)
- Javad Paknahad
- Department of Electrical and Computer Engineering, University of Southern California, Los Angeles, CA, United States of America.,Institute for Technology and Medical Systems (ITEMS), Keck School of Medicine, University of Southern California, Los Angeles, CA, United States of America
| | - Pragya Kosta
- Institute for Technology and Medical Systems (ITEMS), Keck School of Medicine, University of Southern California, Los Angeles, CA, United States of America
| | - Jean-Marie C Bouteiller
- Department of Biomedical Engineering, University of Southern California, Los Angeles, CA, United States of America
| | - Mark S Humayun
- Department of Biomedical Engineering, University of Southern California, Los Angeles, CA, United States of America.,Department of Ophthalmology, University of Southern California, Los Angeles, CA, United States of America
| | - Gianluca Lazzi
- Department of Electrical and Computer Engineering, University of Southern California, Los Angeles, CA, United States of America.,Institute for Technology and Medical Systems (ITEMS), Keck School of Medicine, University of Southern California, Los Angeles, CA, United States of America.,Department of Biomedical Engineering, University of Southern California, Los Angeles, CA, United States of America.,Department of Ophthalmology, University of Southern California, Los Angeles, CA, United States of America
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28
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Otgondemberel Y, Roh H, Fried SI, Im M. Spiking Characteristics of Network-Mediated Responses Arising in Direction-Selective Ganglion Cells of Rabbit and Mouse Retinas to Electric Stimulation for Retinal Prostheses. IEEE Trans Neural Syst Rehabil Eng 2021; 29:2445-2455. [PMID: 34784280 PMCID: PMC8654582 DOI: 10.1109/tnsre.2021.3128878] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
To restore the sight of individuals blinded by outer retinal degeneration, numerous retinal prostheses have been developed. However, the performance of those implants is still hampered by some factors including the lack of comprehensive understanding of the electrically-evoked responses arising in various retinal ganglion cell (RGC) types. In this study, we characterized the electrically-evoked network-mediated responses (hereafter referred to as electric responses) of ON-OFF direction-selective (DS) RGCs in rabbit and mouse retinas for the first time. Interestingly, both species in common demonstrated strong negative correlations between spike counts of electric responses and direction selective indices (DSIs), suggesting electric stimulation activates inhibitory presynaptic neurons that suppress null direction responses for high direction tuning in their light responses. The DS cells of the two species showed several differences including different numbers of bursts. Also, spiking patterns were more heterogeneous across DS RGCs of rabbits than those of mice. The electric response magnitudes of rabbit DS cells showed positive and negative correlations with ON and OFF light response magnitudes to preferred direction motion, respectively. But the mouse DS cells showed positive correlations in both comparisons. Our Fano Factor (FF) and spike time tiling coefficient (STTC) analyses revealed that spiking consistencies across repeats were reduced in late electric responses in both species. Moreover, the response consistencies of DS RGCs were lower than those of non-DS RGCs. Our results indicate the species-dependent retinal circuits may result in different electric response features and therefore suggest a proper animal model may be crucial in prosthetic researches.
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Vilkhu RS, Madugula SS, Grosberg LE, Gogliettino AR, Hottowy P, Dabrowski W, Sher A, Litke AM, Mitra S, Chichilnisky EJ. Spatially patterned bi-electrode epiretinal stimulation for axon avoidance at cellular resolution. J Neural Eng 2021; 18. [PMID: 34710857 DOI: 10.1088/1741-2552/ac3450] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2021] [Accepted: 10/28/2021] [Indexed: 11/12/2022]
Abstract
Objective.Epiretinal prostheses are designed to restore vision to people blinded by photoreceptor degenerative diseases by stimulating surviving retinal ganglion cells (RGCs), which carry visual signals to the brain. However, inadvertent stimulation of RGCs at their axons can result in non-focal visual percepts, limiting the quality of artificial vision. Theoretical work has suggested that axon activation can be avoided with current stimulation designed to minimize the second spatial derivative of the induced extracellular voltage along the axon. However, this approach has not been verified experimentally at the resolution of single cells.Approach.In this work, a custom multi-electrode array (512 electrodes, 10μm diameter, 60μm pitch) was used to stimulate and record RGCs in macaque retinaex vivoat single-cell, single-spike resolution. RGC activation thresholds resulting from bi-electrode stimulation, which consisted of bipolar currents simultaneously delivered through two electrodes straddling an axon, were compared to activation thresholds from traditional single-electrode stimulation.Main results.On average, across three retinal preparations, the bi-electrode stimulation strategy reduced somatic activation thresholds (∼21%) while increasing axonal activation thresholds (∼14%), thus favoring selective somatic activation. Furthermore, individual examples revealed rescued selective activation of somas that was not possible with any individual electrode.Significance.This work suggests that a bi-electrode epiretinal stimulation strategy can reduce inadvertent axonal activation at cellular resolution, for high-fidelity artificial vision.
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Affiliation(s)
- Ramandeep S Vilkhu
- Department of Electrical Engineering, Stanford University, Stanford, CA, United States of America
| | - Sasidhar S Madugula
- Departments of Neurosurgery, Ophthalmology, and Hansen Experimental Physics Laboratory, Stanford University, Stanford, CA, United States of America
| | - Lauren E Grosberg
- Departments of Neurosurgery, Ophthalmology, and Hansen Experimental Physics Laboratory, Stanford University, Stanford, CA, United States of America
| | - Alex R Gogliettino
- Departments of Neurosurgery, Ophthalmology, and Hansen Experimental Physics Laboratory, Stanford University, Stanford, CA, United States of America
| | - Pawel Hottowy
- Faculty of Physics and Applied Computer Science, AGH University of Science and Technology, Krakow 30-059, Poland
| | - Wladyslaw Dabrowski
- Faculty of Physics and Applied Computer Science, AGH University of Science and Technology, Krakow 30-059, Poland
| | - Alexander Sher
- Santa Cruz Institute for Particle Physics, University of California, Santa Cruz, CA, United States of America
| | - Alan M Litke
- Santa Cruz Institute for Particle Physics, University of California, Santa Cruz, CA, United States of America
| | - Subhasish Mitra
- Department of Electrical Engineering, Stanford University, Stanford, CA, United States of America
| | - E J Chichilnisky
- Departments of Neurosurgery, Ophthalmology, and Hansen Experimental Physics Laboratory, Stanford University, Stanford, CA, United States of America
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30
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Granley J, Beyeler M. A Computational Model of Phosphene Appearance for Epiretinal Prostheses. ANNUAL INTERNATIONAL CONFERENCE OF THE IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. ANNUAL INTERNATIONAL CONFERENCE 2021; 2021:4477-4481. [PMID: 34892213 PMCID: PMC9255280 DOI: 10.1109/embc46164.2021.9629663] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/14/2023]
Abstract
Retinal neuroprostheses are the only FDA-approved treatment option for blinding degenerative diseases. A major outstanding challenge is to develop a computational model that can accurately predict the elicited visual percepts (phosphenes) across a wide range of electrical stimuli. Here we present a phenomenological model that predicts phosphene appearance as a function of stimulus amplitude, frequency, and pulse duration. The model uses a simulated map of nerve fiber bundles in the retina to produce phosphenes with accurate brightness, size, orientation, and elongation. We validate the model on psychophysical data from two independent studies, showing that it generalizes well to new data, even with different stimuli and on different electrodes. Whereas previous models focused on either spatial or temporal aspects of the elicited phosphenes in isolation, we describe a more comprehensive approach that is able to account for many reported visual effects. The model is designed to be flexible and extensible, and can be fit to data from a specific user. Overall this work is an important first step towards predicting visual outcomes in retinal prosthesis users across a wide range of stimuli.
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31
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Abstract
Visual retinal prostheses aim to restore vision for blind individuals who suffer from outer retinal degenerative diseases, such as retinitis pigmentosa and age-related macular degeneration. Perception through retinal prostheses is very limited, but it can be improved by applying object isolation. We used an object isolation algorithm based on integral imaging to isolate objects of interest according to their depth from the camera and applied image processing manipulation to the isolated-object images. Subsequently, we applied a spatial prosthetic vision simulation that converted the isolated-object images to phosphene images. We compared the phosphene images for two types of input images, the original image (before applying object isolation), and the isolated-object image to illustrate the effects of object isolation on simulated prosthetic vision without and with multiple spatial variations of phosphenes, such as size and shape variations, spatial shifts, and dropout rate. The results show an improvement in the perceived shape, contrast, and dynamic range (number of gray levels) of objects in the phosphene image.
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32
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Moleirinho S, Whalen AJ, Fried SI, Pezaris JS. The impact of synchronous versus asynchronous electrical stimulation in artificial vision. J Neural Eng 2021; 18. [PMID: 33900206 DOI: 10.1088/1741-2552/abecf1] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2020] [Accepted: 03/09/2021] [Indexed: 11/12/2022]
Abstract
Visual prosthesis devices designed to restore sight to the blind have been under development in the laboratory for several decades. Clinical translation continues to be challenging, due in part to gaps in our understanding of critical parameters such as how phosphenes, the electrically-generated pixels of artificial vision, can be combined to form images. In this review we explore the effects that synchronous and asynchronous electrical stimulation across multiple electrodes have in evoking phosphenes. Understanding how electrical patterns influence phosphene generation to control object binding and perception of visual form is fundamental to creation of a clinically successful prosthesis.
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Affiliation(s)
- Susana Moleirinho
- Department of Neurosurgery, Massachusetts General Hospital, Boston, MA, United States of America.,Department of Neurosurgery, Harvard Medical School, Boston, MA, United States of America
| | - Andrew J Whalen
- Department of Neurosurgery, Massachusetts General Hospital, Boston, MA, United States of America.,Department of Neurosurgery, Harvard Medical School, Boston, MA, United States of America
| | - Shelley I Fried
- Department of Neurosurgery, Massachusetts General Hospital, Boston, MA, United States of America.,Department of Neurosurgery, Harvard Medical School, Boston, MA, United States of America.,Boston VA Healthcare System, Boston, MA, United States of America
| | - John S Pezaris
- Department of Neurosurgery, Massachusetts General Hospital, Boston, MA, United States of America.,Department of Neurosurgery, Harvard Medical School, Boston, MA, United States of America
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33
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Hadjinicolaou AE, Meffin H, Maturana MI, Cloherty SL, Ibbotson MR. Prosthetic vision: devices, patient outcomes and retinal research. Clin Exp Optom 2021; 98:395-410. [DOI: 10.1111/cxo.12342] [Citation(s) in RCA: 28] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2015] [Revised: 07/06/2015] [Accepted: 08/04/2015] [Indexed: 12/11/2022] Open
Affiliation(s)
- Alex E Hadjinicolaou
- National Vision Research Institute, Australian College of Optometry, Carlton, Victoria, Australia,
- ARC Centre of Excellence for Integrative Brain Function and Department of Optometry and Vision Sciences, University of Melbourne, Parkville, Victoria, Australia,
| | - Hamish Meffin
- National Vision Research Institute, Australian College of Optometry, Carlton, Victoria, Australia,
- ARC Centre of Excellence for Integrative Brain Function and Department of Optometry and Vision Sciences, University of Melbourne, Parkville, Victoria, Australia,
| | - Matias I Maturana
- National Vision Research Institute, Australian College of Optometry, Carlton, Victoria, Australia,
- Department of Electrical and Electronic Engineering, The University of Melbourne, Parkville, Victoria, Australia,
| | - Shaun L Cloherty
- National Vision Research Institute, Australian College of Optometry, Carlton, Victoria, Australia,
- ARC Centre of Excellence for Integrative Brain Function and Department of Optometry and Vision Sciences, University of Melbourne, Parkville, Victoria, Australia,
- Department of Electrical and Electronic Engineering, The University of Melbourne, Parkville, Victoria, Australia,
| | - Michael R Ibbotson
- National Vision Research Institute, Australian College of Optometry, Carlton, Victoria, Australia,
- ARC Centre of Excellence for Integrative Brain Function and Department of Optometry and Vision Sciences, University of Melbourne, Parkville, Victoria, Australia,
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34
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Paknahad J, Loizos K, Yue L, Humayun MS, Lazzi G. Color and cellular selectivity of retinal ganglion cell subtypes through frequency modulation of electrical stimulation. Sci Rep 2021; 11:5177. [PMID: 33664347 PMCID: PMC7933163 DOI: 10.1038/s41598-021-84437-w] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2020] [Accepted: 02/15/2021] [Indexed: 01/31/2023] Open
Abstract
Epiretinal prostheses aim at electrically stimulating the inner most surviving retinal cells-retinal ganglion cells (RGCs)-to restore partial sight to the blind. Recent tests in patients with epiretinal implants have revealed that electrical stimulation of the retina results in the percept of color of the elicited phosphenes, which depends on the frequency of stimulation. This paper presents computational results that are predictive of this finding and further support our understanding of the mechanisms of color encoding in electrical stimulation of retina, which could prove pivotal for the design of advanced retinal prosthetics that elicit both percept and color. This provides, for the first time, a directly applicable "amplitude-frequency" stimulation strategy to "encode color" in future retinal prosthetics through a predictive computational tool to selectively target small bistratified cells, which have been shown to contribute to "blue-yellow" color opponency in the retinal circuitry. The presented results are validated with experimental data reported in the literature and correlated with findings in blind patients with a retinal prosthetic implant collected by our group.
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Affiliation(s)
- Javad Paknahad
- grid.42505.360000 0001 2156 6853Department of Electrical Engineering, University of Southern California, Los Angeles, CA USA ,grid.42505.360000 0001 2156 6853The Institute for Technology and Medical Systems (ITEMS), Keck School of Medicine, University of Southern California, Los Angeles, CA USA
| | - Kyle Loizos
- grid.42505.360000 0001 2156 6853The Institute for Technology and Medical Systems (ITEMS), Keck School of Medicine, University of Southern California, Los Angeles, CA USA
| | - Lan Yue
- grid.42505.360000 0001 2156 6853Roski Eye Institute, University of Southern California, Los Angeles, CA USA
| | - Mark S. Humayun
- grid.42505.360000 0001 2156 6853Roski Eye Institute, University of Southern California, Los Angeles, CA USA ,grid.42505.360000 0001 2156 6853Departments of Ophthalmology and Biomedical Engineering, University of Southern California, Los Angeles, CA USA
| | - Gianluca Lazzi
- grid.42505.360000 0001 2156 6853Department of Electrical Engineering, University of Southern California, Los Angeles, CA USA ,grid.42505.360000 0001 2156 6853The Institute for Technology and Medical Systems (ITEMS), Keck School of Medicine, University of Southern California, Los Angeles, CA USA ,grid.42505.360000 0001 2156 6853Departments of Ophthalmology and Biomedical Engineering, University of Southern California, Los Angeles, CA USA
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Gauvain G, Akolkar H, Chaffiol A, Arcizet F, Khoei MA, Desrosiers M, Jaillard C, Caplette R, Marre O, Bertin S, Fovet CM, Demilly J, Forster V, Brazhnikova E, Hantraye P, Pouget P, Douar A, Pruneau D, Chavas J, Sahel JA, Dalkara D, Duebel J, Benosman R, Picaud S. Optogenetic therapy: high spatiotemporal resolution and pattern discrimination compatible with vision restoration in non-human primates. Commun Biol 2021; 4:125. [PMID: 33504896 PMCID: PMC7840970 DOI: 10.1038/s42003-020-01594-w] [Citation(s) in RCA: 60] [Impact Index Per Article: 20.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2020] [Accepted: 12/09/2020] [Indexed: 01/06/2023] Open
Abstract
Vision restoration is an ideal medical application for optogenetics, because the eye provides direct optical access to the retina for stimulation. Optogenetic therapy could be used for diseases involving photoreceptor degeneration, such as retinitis pigmentosa or age-related macular degeneration. We describe here the selection, in non-human primates, of a specific optogenetic construct currently tested in a clinical trial. We used the microbial opsin ChrimsonR, and showed that the AAV2.7m8 vector had a higher transfection efficiency than AAV2 in retinal ganglion cells (RGCs) and that ChrimsonR fused to tdTomato (ChR-tdT) was expressed more efficiently than ChrimsonR. Light at 600 nm activated RGCs transfected with AAV2.7m8 ChR-tdT, from an irradiance of 1015 photons.cm−2.s−1. Vector doses of 5 × 1010 and 5 × 1011 vg/eye transfected up to 7000 RGCs/mm2 in the perifovea, with no significant immune reaction. We recorded RGC responses from a stimulus duration of 1 ms upwards. When using the recorded activity to decode stimulus information, we obtained an estimated visual acuity of 20/249, above the level of legal blindness (20/400). These results lay the groundwork for the ongoing clinical trial with the AAV2.7m8 - ChR-tdT vector for vision restoration in patients with retinitis pigmentosa. Gauvain et al demonstrate that optogenetic therapy using the AAV2.7m8- ChR-tdT construct can partially restore vision in non-human primates to levels above those considered legally-blind. This study enables the identification of the most suitable construct for ongoing clinical trials attempting vision restoration in patients with retinitis pigmentosa.
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Affiliation(s)
- Gregory Gauvain
- Sorbonne Université, INSERM, CNRS, Institut de la Vision, 17 rue Moreau, F-75012, Paris, France.
| | - Himanshu Akolkar
- Sorbonne Université, INSERM, CNRS, Institut de la Vision, 17 rue Moreau, F-75012, Paris, France.,Department of Ophthalmology, University Pittsburgh Medical Center, Pittsburgh, PA, USA
| | - Antoine Chaffiol
- Sorbonne Université, INSERM, CNRS, Institut de la Vision, 17 rue Moreau, F-75012, Paris, France
| | - Fabrice Arcizet
- Sorbonne Université, INSERM, CNRS, Institut de la Vision, 17 rue Moreau, F-75012, Paris, France
| | - Mina A Khoei
- Sorbonne Université, INSERM, CNRS, Institut de la Vision, 17 rue Moreau, F-75012, Paris, France
| | - Mélissa Desrosiers
- Sorbonne Université, INSERM, CNRS, Institut de la Vision, 17 rue Moreau, F-75012, Paris, France
| | - Céline Jaillard
- Sorbonne Université, INSERM, CNRS, Institut de la Vision, 17 rue Moreau, F-75012, Paris, France
| | - Romain Caplette
- Sorbonne Université, INSERM, CNRS, Institut de la Vision, 17 rue Moreau, F-75012, Paris, France
| | - Olivier Marre
- Sorbonne Université, INSERM, CNRS, Institut de la Vision, 17 rue Moreau, F-75012, Paris, France
| | - Stéphane Bertin
- CHNO des Quinze-Vingts, INSERM-DGOS CIC 1423, 28 rue de Charenton, F-75012, Paris, France
| | - Claire-Maelle Fovet
- Département des Sciences du Vivant (DSV), MIRcen, Institut d'imagerie Biomédicale (I2BM), Commissariat à l'Energie Atomique et aux Energies Alternatives (CEA), 92260, Fontenay-aux-Roses, France
| | - Joanna Demilly
- Département des Sciences du Vivant (DSV), MIRcen, Institut d'imagerie Biomédicale (I2BM), Commissariat à l'Energie Atomique et aux Energies Alternatives (CEA), 92260, Fontenay-aux-Roses, France
| | - Valérie Forster
- Sorbonne Université, INSERM, CNRS, Institut de la Vision, 17 rue Moreau, F-75012, Paris, France
| | - Elena Brazhnikova
- Sorbonne Université, INSERM, CNRS, Institut de la Vision, 17 rue Moreau, F-75012, Paris, France
| | - Philippe Hantraye
- Département des Sciences du Vivant (DSV), MIRcen, Institut d'imagerie Biomédicale (I2BM), Commissariat à l'Energie Atomique et aux Energies Alternatives (CEA), 92260, Fontenay-aux-Roses, France
| | - Pierre Pouget
- ICM, UMRS 1127 UPMC - U 1127 INSERM - UMR 7225 CNRS, Paris, France
| | - Anne Douar
- Gensight Biologics, 74 rue du faubourg Saint Antoine, F-75012, Paris, France
| | - Didier Pruneau
- Gensight Biologics, 74 rue du faubourg Saint Antoine, F-75012, Paris, France
| | - Joël Chavas
- Gensight Biologics, 74 rue du faubourg Saint Antoine, F-75012, Paris, France
| | - José-Alain Sahel
- Sorbonne Université, INSERM, CNRS, Institut de la Vision, 17 rue Moreau, F-75012, Paris, France.,Department of Ophthalmology, University Pittsburgh Medical Center, Pittsburgh, PA, USA.,CHNO des Quinze-Vingts, INSERM-DGOS CIC 1423, 28 rue de Charenton, F-75012, Paris, France
| | - Deniz Dalkara
- Sorbonne Université, INSERM, CNRS, Institut de la Vision, 17 rue Moreau, F-75012, Paris, France
| | - Jens Duebel
- Sorbonne Université, INSERM, CNRS, Institut de la Vision, 17 rue Moreau, F-75012, Paris, France
| | - Ryad Benosman
- Sorbonne Université, INSERM, CNRS, Institut de la Vision, 17 rue Moreau, F-75012, Paris, France.,Department of Ophthalmology, University Pittsburgh Medical Center, Pittsburgh, PA, USA
| | - Serge Picaud
- Sorbonne Université, INSERM, CNRS, Institut de la Vision, 17 rue Moreau, F-75012, Paris, France.
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36
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Paknahad J, Loizos K, Humayun M, Lazzi G. Targeted Stimulation of Retinal Ganglion Cells in Epiretinal Prostheses: A Multiscale Computational Study. IEEE Trans Neural Syst Rehabil Eng 2020; 28:2548-2556. [PMID: 32991284 DOI: 10.1109/tnsre.2020.3027560] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
Retinal prostheses aim at restoring partial sight to patients that are blind due to retinal degenerative diseases by electrically stimulating the surviving healthy retinal neurons. Ideally, the electrical stimulation of the retina is intended to induce localized, focused, percepts only; however, some epiretinal implant subjects have reported seeing elongated phosphenes in a single electrode stimulation due to the axonal activation of retinal ganglion cells (RGCs). This issue can be addressed by properly devising stimulation waveforms so that the possibility of inducing axonal activation of RGCs is minimized. While strategies to devise electrical stimulation waveforms to achieve a focal RGCs response have been reported in literature, the underlying mechanisms are not well understood. This article intends to address this gap; we developed morphologically and biophysically realistic computational models of two classified RGCs: D1-bistratified and A2-monostratified. Computational results suggest that the sodium channel band (SOCB) is less sensitive to modulations in stimulation parameters than the distal axon (DA), and DA stimulus threshold is less sensitive to physiological differences among RGCs. Therefore, over a range of RGCs distal axon diameters, short-pulse symmetric biphasic waveforms can enhance the stimulation threshold difference between the SOCB and the DA. Appropriately designed waveforms can avoid axonal activation of RGCs, implying a consequential reduction of undesired strikes in the visual field.
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Muralidharan M, Guo T, Shivdasani MN, Tsai D, Fried S, Cameron M, Morley JW, Dokos S, Lovell NH. Towards Controlling Functionally-Distinct Retinal Ganglion Cells In Degenerate Retina. ANNUAL INTERNATIONAL CONFERENCE OF THE IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. ANNUAL INTERNATIONAL CONFERENCE 2020; 2020:3598-3601. [PMID: 33018781 DOI: 10.1109/embc44109.2020.9176595] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
Present retinal neuroprostheses have limited performance capabilities due to indiscriminate activation of different neural pathways. Based on our success in differentially activating ON and OFF cells using high frequency stimuli in a healthy retina, in this study we explored whether we could achieve similar differential activation between these two cell types but in degenerate retina. We found that after blocking the synaptic network, ON retinal ganglion cells (RGCs) could be differentially activated at higher frequencies (4 - 6 kHz) and amplitudes (200 - 240 µA), and OFF RGCs at relatively lower amplitudes (80 - 160 µA) across all tested frequencies. We further found that both cell types could be controlled by quickly modulating the frequency using short stimulation bursts. This work takes us one step closer to reducing the likelihood of indiscriminate activation of RGCs by accurately controlling the activation of functionally-distinct neural pathways.
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Straňák Z, Kousal B, Ardan T, Veith M. Innovative strategies for treating retinal diseases. ACTA ACUST UNITED AC 2020; 75:287-295. [PMID: 32911944 DOI: 10.31348/2019/6/1] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
OBJECTIVE The aim of this comprehensive paper is to acquaint the readers with innovative approaches in the treatment of retinal diseases, which could in the coming years to get into clinical practice. Retinal prostheses, retinal pigment epithelial (RPE) transplantation, gene therapy and optogenetics will be described in this paper. METHODOLOGY Describing the basic characteristics and mechanisms of different types of therapy and subsequently literary minireview clarifying the current state of knowledge in the area. RESULTS Retinal prostheses, RPE transplantation, gene therapy and optogenetics offer yet unexplored possibilities and are considered as the future of treatment of retinal diseases where classical pharmacotherapy or surgical treatment are no longer sufficient. However, all these methods challenge not only in the innovative technical implementation itself, but also for the ethical, administrative and economic demands. CONCLUSION There will be certainly interesting development in the treatment of retinal diseases, but it is not possible to fully estimate which modality of treatment will be dominant in the future.
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Muralidharan M, Guo T, Shivdasani MN, Tsai D, Fried S, Li L, Dokos S, Morley JW, Lovell NH. Neural activity of functionally different retinal ganglion cells can be robustly modulated by high-rate electrical pulse trains. J Neural Eng 2020; 17:045013. [DOI: 10.1088/1741-2552/ab9a97] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
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Haji Ghaffari D, Finn KE, Jeganathan VSE, Patel U, Wuyyuru V, Roy A, Weiland JD. The effect of waveform asymmetry on perception with epiretinal prostheses. J Neural Eng 2020; 17:045009. [PMID: 32590371 DOI: 10.1088/1741-2552/aba07e] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Objective Retinal prosthetic implants have helped improve vision in patients blinded by photoreceptor degeneration. Retinal implant users report improvements in light perception and performing visual tasks, but their ability to perceive shapes and letters is limited due to the low precision of retinal activation, which is exacerbated by axonal stimulation and high perceptual thresholds. A previous in vitro study in our lab used calcium imaging to measure the spatial activity of mouse retinal ganglion cells (RGCs) in response to electrical stimulation. Based on this study, symmetric anodic-first (SA) stimulation effectively avoided axonal activation and asymmetric anodic-first stimulation (AA) with duration ratios (ratio of the anodic to cathodic phase) greater than 10 reduced RGC activation thresholds significantly. Applying these novel stimulation strategies in clinic may increase perception precision and improve the overall patient outcomes. Approach We combined human subject testing and computational modeling to further examine the effect of SA and AA stimuli on perception shapes and thresholds for epiretinal stimulation of RGCs. Main results Threshold measurement in three Argus II participants indicated that AA stimulation could increase perception probabilities compared to a standard symmetric cathodic-first (SC) pulse, and this effect can be intensified by addition of an interphae gap (IPG). Our in silico RGC model predicts lower thresholds with AA and asymmetric cathodic-first (AC) stimuli compared to a SC pulse. This effect was more pronounced at shorter pulse widths. The most effective pulse for threshold reduction with short pulse durations (≤0.12 ms) was AA stimulation with small duration ratios (≤5) and long IPGs (≥2 ms). For the 0.5 ms pulse duration, SC stimulation with IPGs longer than 0.5 ms, or asymmetric stimuli with large duration ratios (≥20) were most effective in threshold reduction. Phosphene shape analysis did not reveal a significant change in percept elongation with SA stimulation. However, there was a significant increase in percept size (P < 0.01) with AA stimulation compared to the standard pulse in one participant. Significane Including asymmetric waveform capability will provide more flexible options for optimization and personalized fitting of retinal implants.
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Affiliation(s)
- Dorsa Haji Ghaffari
- Department of Biomedical Engineering, Michigan Engineering, University of Michigan, Ann Arbor, MI 48109, United States of America. Biointerfaces Institute, University of Michigan, Ann Arbor, MI 48109, United States of America
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Ayton LN, Rizzo JF, Bailey IL, Colenbrander A, Dagnelie G, Geruschat DR, Hessburg PC, McCarthy CD, Petoe MA, Rubin GS, Troyk PR. Harmonization of Outcomes and Vision Endpoints in Vision Restoration Trials: Recommendations from the International HOVER Taskforce. Transl Vis Sci Technol 2020; 9:25. [PMID: 32864194 PMCID: PMC7426586 DOI: 10.1167/tvst.9.8.25] [Citation(s) in RCA: 28] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2019] [Accepted: 12/08/2019] [Indexed: 01/05/2023] Open
Abstract
Translational research in vision prosthetics, gene therapy, optogenetics, stem cell and other forms of transplantation, and sensory substitution is creating new therapeutic options for patients with neural forms of blindness. The technical challenges faced by each of these disciplines differ considerably, but they all face the same challenge of how to assess vision in patients with ultra-low vision (ULV), who will be the earliest subjects to receive new therapies. Historically, there were few tests to assess vision in ULV patients. In the 1990s, the field of visual prosthetics expanded rapidly, and this activity led to a heightened need to develop better tests to quantify end points for clinical studies. Each group tended to develop novel tests, which made it difficult to compare outcomes across groups. The common lack of validation of the tests and the variable use of controls added to the challenge of interpreting the outcomes of these clinical studies. In 2014, at the bi-annual International “Eye and the Chip” meeting of experts in the field of visual prosthetics, a group of interested leaders agreed to work cooperatively to develop the International Harmonization of Outcomes and Vision Endpoints in Vision Restoration Trials (HOVER) Taskforce. Under this banner, more than 80 specialists across seven topic areas joined an effort to formulate guidelines for performing and reporting psychophysical tests in humans who participate in clinical trials for visual restoration. This document provides the complete version of the consensus opinions from the HOVER taskforce, which, together with its rules of governance, will be posted on the website of the Henry Ford Department of Ophthalmology (www.artificialvision.org). Research groups or companies that choose to follow these guidelines are encouraged to include a specific statement to that effect in their communications to the public. The Executive Committee of the HOVER Taskforce will maintain a list of all human psychophysical research in the relevant fields of research on the same website to provide an overview of methods and outcomes of all clinical work being performed in an attempt to restore vision to the blind. This website will also specify which scientific publications contain the statement of certification. The website will be updated every 2 years and continue to exist as a living document of worldwide efforts to restore vision to the blind. The HOVER consensus document has been written by over 80 of the world's experts in vision restoration and low vision and provides recommendations on the measurement and reporting of patient outcomes in vision restoration trials.
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Affiliation(s)
- Lauren N Ayton
- Department of Optometry and Vision Sciences and Department of Surgery (Ophthalmology), The University of Melbourne, Parkville, Australia.,Centre for Eye Research Australia, Royal Victorian Eye and Ear Hospital, East Melbourne, Australia
| | - Joseph F Rizzo
- Department of Ophthalmology, Massachusetts Eye and Ear, Harvard Medical School, Boston, MA, USA
| | - Ian L Bailey
- School of Optometry, University of California-Berkeley, Berkeley, CA, USA
| | - August Colenbrander
- Smith-Kettlewell Eye Research Institute and California Pacific Medical Center, San Francisco, CA, USA
| | - Gislin Dagnelie
- Lions Vision Research and Rehabilitation Center, Johns Hopkins Wilmer Eye Institute, Baltimore, MD, USA
| | - Duane R Geruschat
- Lions Vision Research and Rehabilitation Center, Johns Hopkins Wilmer Eye Institute, Baltimore, MD, USA
| | - Philip C Hessburg
- Detroit Institute of Ophthalmology, Henry Ford Health System, Grosse Pointe Park, MI, USA
| | - Chris D McCarthy
- Department of Computer Science & Software Engineering, Swinburne University of Technology, Melbourne, Australia
| | | | - Gary S Rubin
- University College London Institute of Ophthalmology, London, UK
| | - Philip R Troyk
- Armour College of Engineering, Illinois Institute of Technology, Chicago, IL, USA
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Tong W, Hejazi M, Garrett DJ, Esler T, Prawer S, Meffin H, Ibbotson MR. Minimizing axon bundle activation of retinal ganglion cells with oriented rectangular electrodes. J Neural Eng 2020; 17:036016. [PMID: 32375131 DOI: 10.1088/1741-2552/ab909e] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
OBJECTIVE Retinal prostheses aim to restore vision in patients with retinal degenerative diseases, such as age-related macular degeneration and retinitis pigmentosa. By implanting an array of microelectrodes, such a device creates percepts in patients through electrical stimulation of surviving retinal neurons. A challenge for retinal prostheses when trying to return high quality vision is the unintended activation of retinal ganglion cells through the stimulation of passing axon bundles, which leads to patients reporting large, elongated patches of light instead of focal spots. APPROACH In this work, we used calcium imaging to record the responses of retinal ganglion cells to electrical stimulation in explanted retina using rectangular electrodes placed with different orientations relative to the axon bundles. MAIN RESULTS We showed that narrow, rectangular electrodes oriented parallel to the axon bundles can achieve focal stimulation. To further improve the strategy, we studied the impact of different stimulation waveforms and electrode configurations. We found the selectivity for focal stimulation to be higher when using short (33 μs), anodic-first biphasic pulses, with long electrode lengths and at least 50 μm electrode-to-retinal separation. Focal stimulation was, in fact, less selective when the electrodes made direct contact with the retinal surface due to unwanted preferential stimulation of the proximal axon bundles. SIGNIFICANCE When employed in retinal prostheses, the proposed stimulation strategy is expected to provide improved quality of vision to the blind.
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Affiliation(s)
- Wei Tong
- National Vision Research Institute, Australian College of Optometry, Carlton, VIC, Australia. School of Physics, The University of Melbourne, Parkville, VIC, Australia. Department of Vision Science and Optometry, Faculty of Medicine, Dentistry and Health Sciences, The University of Melbourne, Parkville, VIC, Australia
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Im M, Kim SW. Neurophysiological and medical considerations for better-performing microelectronic retinal prostheses. J Neural Eng 2020; 17:033001. [PMID: 32329755 DOI: 10.1088/1741-2552/ab8ca9] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Affiliation(s)
- Maesoon Im
- Center for BioMicrosystems, Brain Science Institute, Korea Institute of Science and Technology (KIST), Seoul, Republic of Korea. Division of Bio-Medical Science & Technology, KIST School, University of Science and Technology (UST), Seoul, Republic of Korea
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Shim S, Eom K, Jeong J, Kim SJ. Retinal Prosthetic Approaches to Enhance Visual Perception for Blind Patients. MICROMACHINES 2020; 11:E535. [PMID: 32456341 PMCID: PMC7281011 DOI: 10.3390/mi11050535] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 04/15/2020] [Revised: 05/22/2020] [Accepted: 05/22/2020] [Indexed: 12/14/2022]
Abstract
Retinal prostheses are implantable devices that aim to restore the vision of blind patients suffering from retinal degeneration, mainly by artificially stimulating the remaining retinal neurons. Some retinal prostheses have successfully reached the stage of clinical trials; however, these devices can only restore vision partially and remain insufficient to enable patients to conduct everyday life independently. The visual acuity of the artificial vision is limited by various factors from both engineering and physiological perspectives. To overcome those issues and further enhance the visual resolution of retinal prostheses, a variety of retinal prosthetic approaches have been proposed, based on optimization of the geometries of electrode arrays and stimulation pulse parameters. Other retinal stimulation modalities such as optics, ultrasound, and magnetics have also been utilized to address the limitations in conventional electrical stimulation. Although none of these approaches have been clinically proven to fully restore the function of a degenerated retina, the extensive efforts made in this field have demonstrated a series of encouraging findings for the next generation of retinal prostheses, and these could potentially enhance the visual acuity of retinal prostheses. In this article, a comprehensive and up-to-date overview of retinal prosthetic strategies is provided, with a specific focus on a quantitative assessment of visual acuity results from various retinal stimulation technologies. The aim is to highlight future directions toward high-resolution retinal prostheses.
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Affiliation(s)
- Shinyong Shim
- Department of Electrical and Computer Engineering, College of Engineering, Seoul National University, Seoul 08826, Korea;
- Inter-university Semiconductor Research Center, College of Engineering, Seoul National University, Seoul 08826, Korea
| | - Kyungsik Eom
- Department of Electronics Engineering, College of Engineering, Pusan National University, Busan 46241, Korea
| | - Joonsoo Jeong
- School of Biomedical Convergence Engineering, College of Information and Biomedical Engineering, Pusan National University, Yangsan 50612, Korea
| | - Sung June Kim
- Department of Electrical and Computer Engineering, College of Engineering, Seoul National University, Seoul 08826, Korea;
- Inter-university Semiconductor Research Center, College of Engineering, Seoul National University, Seoul 08826, Korea
- Institute on Aging, College of Medicine, Seoul National University, Seoul 08826, Korea
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Yue L, Wuyyuru V, Gonzalez-Calle A, Dorn JD, Humayun MS. Retina–electrode interface properties and vision restoration by two generations of retinal prostheses in one patient—one in each eye. J Neural Eng 2020; 17:026020. [DOI: 10.1088/1741-2552/ab7c8f] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
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Höfling L, Oesterle J, Berens P, Zeck G. Probing and predicting ganglion cell responses to smooth electrical stimulation in healthy and blind mouse retina. Sci Rep 2020; 10:5248. [PMID: 32251331 PMCID: PMC7090015 DOI: 10.1038/s41598-020-61899-y] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2019] [Accepted: 02/19/2020] [Indexed: 11/14/2022] Open
Abstract
Retinal implants are used to replace lost photoreceptors in blind patients suffering from retinopathies such as retinitis pigmentosa. Patients wearing implants regain some rudimentary visual function. However, it is severely limited compared to normal vision because non-physiological stimulation strategies fail to selectively activate different retinal pathways at sufficient spatial and temporal resolution. The development of improved stimulation strategies is rendered difficult by the large space of potential stimuli. Here we systematically explore a subspace of potential stimuli by electrically stimulating healthy and blind mouse retina in epiretinal configuration using smooth Gaussian white noise delivered by a high-density CMOS-based microelectrode array. We identify linear filters of retinal ganglion cells (RGCs) by fitting a linear-nonlinear-Poisson (LNP) model. Our stimulus evokes spatially and temporally confined spiking responses in RGC which are accurately predicted by the LNP model. Furthermore, we find diverse shapes of linear filters in the linear stage of the model, suggesting diverse preferred electrical stimuli of RGCs. The linear filter base identified by our approach could provide a starting point of a model-guided search for improved stimuli for retinal prosthetics.
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Affiliation(s)
- Larissa Höfling
- Natural and Medical Sciences Institute at the University of Tübingen, Reutlingen, Germany
- Graduate Training Centre of Neuroscience, University of Tübingen, Tübingen, Germany
- Institute for Ophthalmic Research, University of Tübingen, Tübingen, Germany
- Centre for Integrative Neuroscience, University of Tübingen, Tübingen, Germany
| | - Jonathan Oesterle
- Institute for Ophthalmic Research, University of Tübingen, Tübingen, Germany
| | - Philipp Berens
- Institute for Ophthalmic Research, University of Tübingen, Tübingen, Germany
- Bernstein Center for Computational Neuroscience, University of Tübingen, Tübingen, Germany
- Department of Computer Science, University of Tübingen, Tübingen, Germany
| | - Günther Zeck
- Natural and Medical Sciences Institute at the University of Tübingen, Reutlingen, Germany.
- Bernstein Center for Computational Neuroscience, University of Tübingen, Tübingen, Germany.
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Photovoltaic Restoration of Central Vision in Atrophic Age-Related Macular Degeneration. Ophthalmology 2020; 127:1097-1104. [PMID: 32249038 DOI: 10.1016/j.ophtha.2020.02.024] [Citation(s) in RCA: 102] [Impact Index Per Article: 25.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2019] [Revised: 02/14/2020] [Accepted: 02/18/2020] [Indexed: 11/20/2022] Open
Abstract
PURPOSE Loss of photoreceptors in atrophic age-related macular degeneration results in severe visual impairment, although some peripheral vision is retained. To restore central vision without compromising the residual peripheral field, we developed a wireless photovoltaic retinal implant (PRIMA; Pixium Vision, Paris, France) in which pixels convert images projected from video glasses using near-infrared light into electric current to stimulate the nearby inner retinal neurons. DESIGN We carried out a first-in-human clinical trial to test the safety and efficacy of the prosthesis in patients with geographic atrophy (ClinicalTrials.gov identifier, NCT03333954). PARTICIPANTS Five patients with geographic atrophy zone of at least 3 optic disc diameters, no foveal light perception, and best-corrected visual acuity of 20/400 to 20/1000 in the worse-seeing study eye. METHODS The 2-mm wide, 30-μm thick chip, containing 378 pixels (each 100 μm in diameter), was implanted subretinally in the area of atrophy (absolute scotoma). MAIN OUTCOME MEASURES Anatomic outcomes were assessed with fundus photography and OCT for up to 12 months of follow-up. Prosthetic vision was assessed by mapping light perception, bar orientation, letter recognition, and Landolt C acuity. RESULTS In all patients, the prosthesis was implanted successfully under the macula, although in 2 patients, it was implanted in unintended locations: within the choroid and off center by 2 mm. All 5 patients could perceive white-yellow prosthetic visual patterns with adjustable brightness in the previous scotomata. The 3 with optimal placement of the implant demonstrated prosthetic acuity of 20/460 to 20/550, and the patient with the off-center implant demonstrated 20/800 acuity. Residual natural acuity did not decrease after implantation in any patient. CONCLUSIONS Implantation of the PRIMA did not decrease the residual natural acuity, and it restored visual sensitivity in the former scotoma in each of the 5 patients. In 3 patients with the proper placement of the chip, prosthetic visual acuity was only 10% to 30% less than the level expected from the pixel pitch (20/420). Therefore, the use of optical or electronic magnification in the glasses as well as smaller pixels in future implants may improve visual acuity even further.
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Lyu Q, Lu Z, Li H, Qiu S, Guo J, Sui X, Sun P, Li L, Chai X, Lovell NH. A Three-Dimensional Microelectrode Array to Generate Virtual Electrodes for Epiretinal Prosthesis Based on a Modeling Study. Int J Neural Syst 2020; 30:2050006. [DOI: 10.1142/s0129065720500069] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
Abstract
Despite many advances in the development of retinal prostheses, clinical reports show that current retinal prosthesis subjects can only perceive prosthetic vision with poor visual acuity. A possible approach for improving visual acuity is to produce virtual electrodes (VEs) through electric field modulation. Generating controllable and localized VEs is a crucial factor in effectively improving the perceptive resolution of the retinal prostheses. In this paper, we aimed to design a microelectrode array (MEA) that can produce converged and controllable VEs by current steering stimulation strategies. Through computational modeling, we designed a three-dimensional concentric ring–disc MEA and evaluated its performance with different stimulation strategies. Our simulation results showed that electrode–retina distance (ERD) and inter-electrode distance (IED) can dramatically affect the distribution of electric field. Also the converged VEs could be produced when the parameters of the three-dimensional MEA were appropriately set. VE sites can be controlled by manipulating the proportion of current on each adjacent electrode in a current steering group (CSG). In addition, spatial localization of electrical stimulation can be greatly improved under quasi-monopolar (QMP) stimulation. This study may provide support for future application of VEs in epiretinal prosthesis for potentially increasing the visual acuity of prosthetic vision.
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Affiliation(s)
- Qing Lyu
- School of Biomedical Engineering, Shanghai Jiao Tong University, Shanghai 200240, P. R. China
| | - Zhuofan Lu
- School of Biomedical Engineering, Shanghai Jiao Tong University, Shanghai 200240, P. R. China
| | - Heng Li
- School of Biomedical Engineering, Shanghai Jiao Tong University, Shanghai 200240, P. R. China
| | - Shirong Qiu
- School of Biomedical Engineering, Shanghai Jiao Tong University, Shanghai 200240, P. R. China
| | - Jiahui Guo
- School of Biomedical Engineering, Shanghai Jiao Tong University, Shanghai 200240, P. R. China
| | - Xiaohong Sui
- School of Biomedical Engineering, Shanghai Jiao Tong University, Shanghai 200240, P. R. China
| | - Pengcheng Sun
- School of Biomedical Engineering, Shanghai Jiao Tong University, Shanghai 200240, P. R. China
| | - Liming Li
- School of Biomedical Engineering, Shanghai Jiao Tong University, Shanghai 200240, P. R. China
| | - Xinyu Chai
- School of Biomedical Engineering, Shanghai Jiao Tong University, Shanghai 200240, P. R. China
| | - Nigel H. Lovell
- Graduate School of Biomedical Engineering, University of New South Wales, Sydney, NSW 2052, Australia
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Ophthalmologic Applications. Biomater Sci 2020. [DOI: 10.1016/b978-0-12-816137-1.00072-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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An update on retinal prostheses. Clin Neurophysiol 2019; 131:1383-1398. [PMID: 31866339 DOI: 10.1016/j.clinph.2019.11.029] [Citation(s) in RCA: 85] [Impact Index Per Article: 17.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2019] [Revised: 11/13/2019] [Accepted: 11/14/2019] [Indexed: 11/23/2022]
Abstract
Retinal prostheses are designed to restore a basic sense of sight to people with profound vision loss. They require a relatively intact posterior visual pathway (optic nerve, lateral geniculate nucleus and visual cortex). Retinal implants are options for people with severe stages of retinal degenerative disease such as retinitis pigmentosa and age-related macular degeneration. There have now been three regulatory-approved retinal prostheses. Over five hundred patients have been implanted globally over the past 15 years. Devices generally provide an improved ability to localize high-contrast objects, navigate, and perform basic orientation tasks. Adverse events have included conjunctival erosion, retinal detachment, loss of light perception, and the need for revision surgery, but are rare. There are also specific device risks, including overstimulation (which could cause damage to the retina) or delamination of implanted components, but these are very unlikely. Current challenges include how to improve visual acuity, enlarge the field-of-view, and reduce a complex visual scene to its most salient components through image processing. This review encompasses the work of over 40 individual research groups who have built devices, developed stimulation strategies, or investigated the basic physiology underpinning retinal prostheses. Current technologies are summarized, along with future challenges that face the field.
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