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Effects of different three-dimensional electrodes on epiretinal electrical stimulation by modeling analysis.

Cao X, Sui X, Lyu Q, Li L, Chai X - J Neuroeng Rehabil (2015)

Bottom Line: Increasing the disk electrode's diameter resulted in an increase in threshold current and a decrease in threshold charge density.Non-planar electrodes evoked different activation responses in RGCs than the disk electrode.Non-planar electrodes had larger threshold currents than disk electrodes.

View Article: PubMed Central - PubMed

Affiliation: School of Biomedical Engineering, Shanghai Jiao Tong University, No.800 Dongchuan Road, Shanghai, People's Republic of China. caoxun@sjtu.edu.cn.

ABSTRACT

Background: Epiretinal prostheses have been greatly successful in helping restore the vision of patients blinded by retinal degenerative diseases. The design of stimulating electrodes plays a crucial role in the performance of epiretinal prostheses. The objective of this study was to investigate, through computational modeling analysis, the effects on the excitation of retinal ganglion cells (RGCs) when different three-dimensional (3-D) electrodes were placed in the epiretinal space.

Methods: 3-D finite element models of retinal electrical stimulation were created in COMSOL using a platinum microelectrode, a vitreous body, multi-layered retinal tissue, and retinal pigment epithelium (RPE). Disk and non-planar electrodes with different 3-D structures were used in the epiretinal electrical stimulation. In addition, a multi-RGC model including ionic mechanisms was constructed in NEURON to study the excitability of RGCs in response to epiretinal electrical stimulation by different types of electrodes. Threshold current, threshold charge density, and the activated RGC area were the three key factors used to evaluate the stimulating electrode's performance.

Results: As the electrode-retina distance increased, both threshold current and threshold charge density showed an approximately linear relationship. Increasing the disk electrode's diameter resulted in an increase in threshold current and a decrease in threshold charge density. Non-planar electrodes evoked different activation responses in RGCs than the disk electrode. Concave electrodes produced superior stimulation localization and electrode safety while convex electrodes performed relatively poorly.

Conclusions: Investigation of epiretinal electrical stimulation using different 3-D electrodes would further the optimization of electrode design and help improve the performance of epiretinal prostheses. The combination of finite element analysis in COMSOL and NEURON software provides an efficient way to evaluate the influences of various 3-D electrodes on epiretinal electrical stimulation. Non-planar electrodes had larger threshold currents than disk electrodes. Of the five types of electrodes, concave hemispherical electrodes may be the ideal option, considering their superior stimulation localization and electrode safety.

No MeSH data available.


Related in: MedlinePlus

Responses to stimulation of different electrode shapes. a Comparisons of TC and the electrode geometrical shape at different ERDs. b Comparisons of TCD and the electrode geometrical shape at different ERDs. c Correlation between the active RGC areas and stimulating current for convex electrodes. d Correlation between the activated RGC area and stimulating current for concave electrodes. e Active RGC areas as a function of stimulating current for different electrode shapes at ERD = 40 μm
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Fig10: Responses to stimulation of different electrode shapes. a Comparisons of TC and the electrode geometrical shape at different ERDs. b Comparisons of TCD and the electrode geometrical shape at different ERDs. c Correlation between the active RGC areas and stimulating current for convex electrodes. d Correlation between the activated RGC area and stimulating current for concave electrodes. e Active RGC areas as a function of stimulating current for different electrode shapes at ERD = 40 μm

Mentions: Quantitative comparisons of TC and TCD for the four non-planar electrodes and the Φ = 100 μm disk electrode are shown in Fig. 10(a), (b). TC and TCD showed a nearly linear relationship with ERD for all electrodes. The disk electrode had the lowest TC, and the convex-shaped electrodes had a higher TC than the concave-shaped electrodes. However, the relative comparisons of TCDs for all electrodes depended on ERDs. With a smaller ERD, the disk and concave hemispherical electrodes had the lowest TCDs. But when ERD increased to 80 μm, the TCDs of the concave hemispherical, concave conical, and convex hemispherical electrodes were all lower than that of the disk electrode. There was an approximately linear correlation between activated RGC area and stimulating current for non-planar electrodes (Fig. 10(c), (d)). At ERD = 40 μm, the RGC areas activated by the five differently shaped electrodes were compared, as shown in Fig. 10(e). Under stimulation with the same current (1.25 × TC), the concave electrodes had the smallest activated RGC area (0.013 mm2), followed by the disk electrode (0.018 mm2), the convex hemispherical electrode (0.022 mm2), and the convex conical electrode (0.023 mm2).Fig. 10


Effects of different three-dimensional electrodes on epiretinal electrical stimulation by modeling analysis.

Cao X, Sui X, Lyu Q, Li L, Chai X - J Neuroeng Rehabil (2015)

Responses to stimulation of different electrode shapes. a Comparisons of TC and the electrode geometrical shape at different ERDs. b Comparisons of TCD and the electrode geometrical shape at different ERDs. c Correlation between the active RGC areas and stimulating current for convex electrodes. d Correlation between the activated RGC area and stimulating current for concave electrodes. e Active RGC areas as a function of stimulating current for different electrode shapes at ERD = 40 μm
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4551567&req=5

Fig10: Responses to stimulation of different electrode shapes. a Comparisons of TC and the electrode geometrical shape at different ERDs. b Comparisons of TCD and the electrode geometrical shape at different ERDs. c Correlation between the active RGC areas and stimulating current for convex electrodes. d Correlation between the activated RGC area and stimulating current for concave electrodes. e Active RGC areas as a function of stimulating current for different electrode shapes at ERD = 40 μm
Mentions: Quantitative comparisons of TC and TCD for the four non-planar electrodes and the Φ = 100 μm disk electrode are shown in Fig. 10(a), (b). TC and TCD showed a nearly linear relationship with ERD for all electrodes. The disk electrode had the lowest TC, and the convex-shaped electrodes had a higher TC than the concave-shaped electrodes. However, the relative comparisons of TCDs for all electrodes depended on ERDs. With a smaller ERD, the disk and concave hemispherical electrodes had the lowest TCDs. But when ERD increased to 80 μm, the TCDs of the concave hemispherical, concave conical, and convex hemispherical electrodes were all lower than that of the disk electrode. There was an approximately linear correlation between activated RGC area and stimulating current for non-planar electrodes (Fig. 10(c), (d)). At ERD = 40 μm, the RGC areas activated by the five differently shaped electrodes were compared, as shown in Fig. 10(e). Under stimulation with the same current (1.25 × TC), the concave electrodes had the smallest activated RGC area (0.013 mm2), followed by the disk electrode (0.018 mm2), the convex hemispherical electrode (0.022 mm2), and the convex conical electrode (0.023 mm2).Fig. 10

Bottom Line: Increasing the disk electrode's diameter resulted in an increase in threshold current and a decrease in threshold charge density.Non-planar electrodes evoked different activation responses in RGCs than the disk electrode.Non-planar electrodes had larger threshold currents than disk electrodes.

View Article: PubMed Central - PubMed

Affiliation: School of Biomedical Engineering, Shanghai Jiao Tong University, No.800 Dongchuan Road, Shanghai, People's Republic of China. caoxun@sjtu.edu.cn.

ABSTRACT

Background: Epiretinal prostheses have been greatly successful in helping restore the vision of patients blinded by retinal degenerative diseases. The design of stimulating electrodes plays a crucial role in the performance of epiretinal prostheses. The objective of this study was to investigate, through computational modeling analysis, the effects on the excitation of retinal ganglion cells (RGCs) when different three-dimensional (3-D) electrodes were placed in the epiretinal space.

Methods: 3-D finite element models of retinal electrical stimulation were created in COMSOL using a platinum microelectrode, a vitreous body, multi-layered retinal tissue, and retinal pigment epithelium (RPE). Disk and non-planar electrodes with different 3-D structures were used in the epiretinal electrical stimulation. In addition, a multi-RGC model including ionic mechanisms was constructed in NEURON to study the excitability of RGCs in response to epiretinal electrical stimulation by different types of electrodes. Threshold current, threshold charge density, and the activated RGC area were the three key factors used to evaluate the stimulating electrode's performance.

Results: As the electrode-retina distance increased, both threshold current and threshold charge density showed an approximately linear relationship. Increasing the disk electrode's diameter resulted in an increase in threshold current and a decrease in threshold charge density. Non-planar electrodes evoked different activation responses in RGCs than the disk electrode. Concave electrodes produced superior stimulation localization and electrode safety while convex electrodes performed relatively poorly.

Conclusions: Investigation of epiretinal electrical stimulation using different 3-D electrodes would further the optimization of electrode design and help improve the performance of epiretinal prostheses. The combination of finite element analysis in COMSOL and NEURON software provides an efficient way to evaluate the influences of various 3-D electrodes on epiretinal electrical stimulation. Non-planar electrodes had larger threshold currents than disk electrodes. Of the five types of electrodes, concave hemispherical electrodes may be the ideal option, considering their superior stimulation localization and electrode safety.

No MeSH data available.


Related in: MedlinePlus