Efficacy of supra-choroidal, bipolar, electrical stimulation in a vision prosthesis

Wong, Yan T.; Chen, S. C.; Kerdraon, Yves; Allen, Penelope J; McCombe, Mark; Morley, John W.; Lovell, Nigel H.; Suaning, Gregg J.

doi:10.1109/iembs.2008.4649525

Cited by 12 publications

(16 citation statements)

References 16 publications

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“…With appropriate sizing, this could also provide sufficient charge injection to meet the needs of the more distal implants such as those with suprachoroidal and intrascleral placements, which have recently been proposed by several research groups developing vision prostheses. (28)(29)(30) Despite increases in charge transfer capacity, fabrication challenges may limit the realisation of the benefit of smaller electrodes. As shown in Fig.…”

Section: Discussionmentioning

confidence: 99%

Variation in Performance of Platinum Electrodes with Size and Surface Roughness

2012

Sensors and Materials

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Platinum (Pt) has been extensively used in medical electrodes and is proposed as a candidate for stimulation sites in retinal neuroprostheses due to its relative inertness and stability in biological environments. However, as implantable therapeutic devices are created with increasingly smaller dimensions, it is necessary to ensure that electrode properties are optimised. In this study, we present the variation in Pt electrode performance, which occurs as a result of reducing the electrode size. Additionally, the feasibility of laser roughening these electrodes is considered with respect to stability under chronic stimulation. It is shown that as the electrode diameter is decreased, the charge storage capacity (CSC) per unit area is increased twofold. Additionally, the frequency-dependent impedance per unit area decreases, resulting in an increase in the charge injection limit of up to 3.4 times in the biological environment. Finally, the stability of laser-roughened electrodes is demonstrated by continuous biphasic stimulation for more than 1 billion pulses at levels consistent with the activation of the neural retina.

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Section: Discussionmentioning

confidence: 99%

Variation in Performance of Platinum Electrodes with Size and Surface Roughness

2012

Sensors and Materials

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“…20,21 The subretinal approach improves the mechanical stability; however, it involves complex surgery to detach the retina partially from the pigment epithelium at the implantation site. 22 From these potential limitations, the suprachoroidal approach [23][24][25] was developed, allowing the electrode array to be inserted and positioned with a simple scleral incision. 26 The suprachoroidal space positions the electrode between two mechanically robust layers of the retina (choroid and sclera), and is unlikely to cause fibrosis of the pigment epithelium.…”

Section: Resultsmentioning

confidence: 99%

Current Steering in Retinal Stimulation via a Quasimonopolar Stimulation Paradigm

Matteucci

Chen

Tsai

et al. 2013

Invest. Ophthalmol. Vis. Sci.

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PURPOSE. Research to restore some degree of vision to patients suffering from retinal degeneration is becoming increasingly more promising. Several groups have chosen electrical stimulation of the remaining network of a degenerate retina as a means to generate discrete light percepts (phosphenes). Approaches vary significantly, with the greatest difference being the location of the stimulating electrode itself.METHODS. Suprachoroidal positioning offers excellent mechanical stability and surgical simplicity; however, at the cost of activation thresholds and focused stimulation due to the distance from the electrodes to the target neurons. Past studies proposed a hexapolar electrode configuration to focus the cortical activation and minimize cross-talk between electrodes during concurrent stimulation. The high impedance nature of the choroid and pigment epithelium, however, cause current to shunt between the stimulating and return electrodes, resulting in even higher activation thresholds. In our study, we analyzed the effect of stimulating the feline retina using a quasimonopolar stimulation by simultaneously stimulating a hexapolar and distant monopolar return configurations. RESULTS.Results of in vivo studies showed that quasimonopolar stimulation can be used to maintain the activation containment properties of hexapolar stimulation, while lowering the activation threshold to values almost equivalent to those of monopolar stimulation.CONCLUSIONS. The optimal stimulus was found to be composed of a subthreshold monopolar stimulus combined with a suprathreshold hexapolar stimulation. This resulted in a decrease of activation threshold of 60% with respect to hexapolar alone, but with no discernible deleterious effect on the charge containment of a pure hexapolar stimulation.

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“…where (8) Thus, the variation of becomes the dominant factor. This variation is minimized by increasing the size of the transistors in the bias network and by distributing a current that bias these Fig.…”

Section: B Calibrationmentioning

confidence: 98%

A Fully Intraocular High-Density Self-Calibrating Epiretinal Prosthesis

Monge

Raj

Nazari

et al. 2013

IEEE Trans. Biomed. Circuits Syst.

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This paper presents a fully intraocular self-calibrating epiretinal prosthesis with 512 independent channels in 65 nm CMOS. A novel digital calibration technique matches the biphasic currents of each channel independently while the calibration circuitry is shared among every 4 channels. Dual-band telemetry for power and data with on-chip rectifier and clock recovery reduces the number of off-chip components. The rectifier utilizes unidirectional switches to prevent reverse conduction loss in the power transistors and achieves an efficiency > 80%. The data telemetry implements a phase-shift keying (PSK) modulation scheme and supports data rates up to 20 Mb/s. The system occupies an area of 4.5 ×3.1 mm². It features a pixel size of 0.0169 mm² and arbitrary waveform generation per channel. In vitro measurements performed on a Pt/Ir concentric bipolar electrode in phosphate buffered saline (PBS) are presented. A statistical measurement over 40 channels from 5 different chips shows a current mismatch with μ = 1.12 μA and σ = 0.53 μA. The chip is integrated with flexible MEMS origami coils and parylene substrate to provide a fully intraocular implant.

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Efficacy of supra-choroidal, bipolar, electrical stimulation in a vision prosthesis

Cited by 12 publications

References 16 publications

Variation in Performance of Platinum Electrodes with Size and Surface Roughness

Variation in Performance of Platinum Electrodes with Size and Surface Roughness

Current Steering in Retinal Stimulation via a Quasimonopolar Stimulation Paradigm

A Fully Intraocular High-Density Self-Calibrating Epiretinal Prosthesis

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