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Gonzalez Calle A, Paknahad J, Pollalis D, Kosta P, Thomas B, Tew BY, Salhia B, Louie S, Lazzi G, Humayun M. An extraocular electrical stimulation approach to slow down the progression of retinal degeneration in an animal model. Sci Rep 2023; 13:15924. [PMID: 37741821 PMCID: PMC10517961 DOI: 10.1038/s41598-023-40547-1] [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: 04/26/2023] [Accepted: 08/12/2023] [Indexed: 09/25/2023] Open
Abstract
Retinal diseases such as retinitis pigmentosa (RP) and age-related macular degeneration (AMD) are characterized by unrelenting neuronal death. However, electrical stimulation has been shown to induce neuroprotective changes in the retina capable of slowing down the progression of retinal blindness. In this work, a multi-scale computational model and modeling platform were used to design electrical stimulation strategies to better target the bipolar cells (BCs), that along with photoreceptors are affected at the early stage of retinal degenerative diseases. Our computational findings revealed that biphasic stimulus pulses of long pulse duration could decrease the activation threshold of BCs, and the differential stimulus threshold between ganglion cells (RGCs) and BCs, offering the potential of targeting the BCs during the early phase of degeneration. In vivo experiments were performed to evaluate the electrode placement and parameters found to target bipolar cells and evaluate the safety and efficacy of the treatment. Results indicate that the proposed transcorneal Electrical Stimulation (TES) strategy can attenuate retinal degeneration in a Royal College of Surgeon (RCS) rodent model, offering the potential to translate this work to clinical practice.
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Affiliation(s)
- Alejandra Gonzalez Calle
- Department of Ophthalmology, USC Roski Eye Institute, Keck School of Medicine, University of Southern California, Los Angeles, CA, 90033, USA
- USC Ginsburg Institute for Biomedical Therapeutics, University of Southern California, Los Angeles, CA, 90033, USA
| | - Javad Paknahad
- USC Ginsburg Institute for Biomedical Therapeutics, University of Southern California, Los Angeles, CA, 90033, USA
- USC Institute for Technology and Medical Systems Innovation, Los Angeles, CA, 90033, USA
| | - Dimitrios Pollalis
- Department of Ophthalmology, USC Roski Eye Institute, Keck School of Medicine, University of Southern California, Los Angeles, CA, 90033, USA
- USC Ginsburg Institute for Biomedical Therapeutics, University of Southern California, Los Angeles, CA, 90033, USA
| | - Pragya Kosta
- USC Ginsburg Institute for Biomedical Therapeutics, University of Southern California, Los Angeles, CA, 90033, USA
- USC Institute for Technology and Medical Systems Innovation, Los Angeles, CA, 90033, USA
| | - Biju Thomas
- USC Ginsburg Institute for Biomedical Therapeutics, University of Southern California, Los Angeles, CA, 90033, USA
| | - Ben Yi Tew
- USC Ginsburg Institute for Biomedical Therapeutics, University of Southern California, Los Angeles, CA, 90033, USA
- USC Department of Translational Genomics, Keck School of Medicine, University of Southern California, Los Angeles, CA, 90033, USA
| | - Bodour Salhia
- USC Ginsburg Institute for Biomedical Therapeutics, University of Southern California, Los Angeles, CA, 90033, USA
- USC Department of Translational Genomics, Keck School of Medicine, University of Southern California, Los Angeles, CA, 90033, USA
| | - Stan Louie
- USC Ginsburg Institute for Biomedical Therapeutics, University of Southern California, Los Angeles, CA, 90033, USA
- USC Mann School of Pharmacy and Pharmaceutical Sciences, University of Southern California, Los Angeles, CA, 90089, USA
| | - Gianluca Lazzi
- USC Ginsburg Institute for Biomedical Therapeutics, University of Southern California, Los Angeles, CA, 90033, USA
- USC Institute for Technology and Medical Systems Innovation, Los Angeles, CA, 90033, USA
| | - Mark Humayun
- Department of Ophthalmology, USC Roski Eye Institute, Keck School of Medicine, University of Southern California, Los Angeles, CA, 90033, USA.
- USC Ginsburg Institute for Biomedical Therapeutics, University of Southern California, Los Angeles, CA, 90033, USA.
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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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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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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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Paknahad J, Loizos K, Humayun M, Lazzi G. Responsiveness of Retinal Ganglion Cells Through Frequency Modulation of Electrical Stimulation: A Computational Modeling Study .. ANNUAL INTERNATIONAL CONFERENCE OF THE IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. ANNUAL INTERNATIONAL CONFERENCE 2020; 2020:3393-3398. [PMID: 33018732 DOI: 10.1109/embc44109.2020.9176125] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
Abstract
Electrical stimulation of surviving retinal neurons has proven effective in restoring sight to totally blind patients affected by retinal degenerative diseases. Morphological and biophysical differences among retinal ganglion cells (RGCs) are important factors affecting their response to epiretinal electrical stimulation. Although detailed models of ON and OFF RGCs have already been investigated, here we developed morphologically and biophysically realistic computational models of two classified RGCs, D1-bistratified and A2-monostratified, and analyzed their response to alternations in stimulation frequency (up to 200 Hz). Results show that the D1-bistratified cell is more responsive to high frequency stimulation compared to the A2-monostratified cell. This differential RGCs response suggests a potential avenue for selective activation, and in turn different encoded percept of RGCs.
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Song X, Guo T, Shivdasani MN, Dokos S, Lovell NH, Li X, Qiu S, Li T, Zheng S, Li L. Creation of virtual channels in the retina using synchronous and asynchronous stimulation - a modelling study. J Neural Eng 2020; 17. [PMID: 33086210 DOI: 10.1088/1741-2552/abc3a9] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2020] [Accepted: 10/21/2020] [Indexed: 11/11/2022]
Abstract
OBJECTIVE Implantable retinal prostheses aim to provide artificial vision to those suffering from retinal degenerative diseases by electrically stimulating the remaining retinal neurons using a multi-electrode array. The spatial resolution of these devices can be improved by creation of so-called virtual channels (VCs) that are commonly achieved through synchronized stimulation of multiple electrodes. It is largely unclear though if VCs can be created using asynchronous stimulation, which was the primary aim of this study. APPROACH A computational model of multi-layered retina and epi-retinal dual-electrode stimulation was developed to simulate the neural activity of populations of retinal ganglion cells (RGCs) using the VC strategy under both synchronous and asynchronous stimulation conditions. MAIN RESULTS Our simulation suggests that VCs can be created using asynchronous stimulation. VC performance under both synchronous and asynchronous stimulation conditions can be improved by optimizing stimulation parameters such as current intensity, current ratio (α) between two electrodes, electrode spacing and the stimulation waveform. In particular, two VC performance measures; (1) linear displacement of the centroid of RGC activation, and (2) the RGC activation size consistency as a function of different current ratios α, have comparable performance under asynchronous and synchronous stimulation with appropriately selected stimulation parameters. SIGNIFICANCE Our findings support the possibility of creating VCs in the retina under both synchronous and asynchronous stimulation conditions. The results provide theoretical evidence for future retinal prosthesis designs with higher spatial resolution and power efficiency whilst reducing the number of current sources required to achieve these outcomes.
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Affiliation(s)
- Xiaoyu Song
- , Shanghai Jiao Tong University, Shanghai, 200240, CHINA
| | - Tianruo Guo
- GSBME, UNSW, Sydney, New South Wales, 2052, AUSTRALIA
| | - Mohit N Shivdasani
- Graduate School of Biomedical Engineering, University of New South Wales, Lower Ground, Samuels Building (F25), Kensington, New South Wales, AUSTRALIA
| | - Socrates Dokos
- Graduate School of Biomedical Engineering, The University of New South Wales, Sydney 2052, New South Wales, Sydney, New South Wales, 2052, AUSTRALIA
| | - Nigel H Lovell
- Graduate School of Biomedical Engineering, University of New South Wales, Sydney, NSW 2052, Sydney, 2052, AUSTRALIA
| | - Xinxin Li
- School of Biomedical Engineering, Shanghai Jiao Tong University, Shanghai, CHINA
| | - Shirong Qiu
- School of Biomedical Engineering, Shanghai Jiao Tong University, Shanghai, CHINA
| | - Tong Li
- School of Biomedical Engineering, Shanghai Jiao Tong University, Shanghai, CHINA
| | - Shiwei Zheng
- School of Biomedical Engineering, Shanghai Jiao Tong University, Shanghai, CHINA
| | - Liming Li
- School of Biomedical Engineering, Shanghai Jiao Tong University, Shanghai 200240, Shanghai, CHINA
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