Safety assessment of semichronic suprachoroidal electrical stimulation to rabbit retina

Kanda

et al. 2017

Sensors and Materials

Retinal prostheses for blindness due to retinal photoreceptor degeneration stimulate the retina electrically to evoke a pseudolight sensation (phosphenes). Although rectangular pulses of electrical stimulation are commonly used in retinal prostheses, it remains unclear whether nonrectangular pulses are effective in evoking this response. Here, we conducted in vivo electrophysiological experiments to compare the effectiveness of sinusoidal and rectangular pulses. Biphasic sinusoidal pulses (cathodic-first) applied suprachoroidally and transretinally to the rat eye elicited larger field responses in the superior colliculus than did rectangular pulses. The threshold charge for the evoked response of the sinusoidal pulse was significantly lower than that of the rectangular pulse, suggesting that a sinusoidal pulse is more effective than a rectangular pulse in our retinal prosthesis. Because a sinusoidal pulse can evoke phosphenes with a small charge magnitude even if the electrode area is reduced, the charge density does not increase; thus, the pulse can stimulate the retina without causing tissue injury. Because the sinusoidal pulse allows us to reduce the electrode area, it is possible that phosphenes can be localized to a smaller area by limiting the range of stimulated retinal ganglion cells. Therefore, high resolution of retinal prostheses using the sinusoidal pulse can be expected.

Section: Discussionmentioning

confidence: 88%

Section: Discussionmentioning

confidence: 99%

Sinusoidal Electrical Pulse More Efficiently Evokes Retinal Excitation than Rectangular Electrical Pulse in Retinal Prostheses

Nakano

Kanda

et al. 2017

Sensors and Materials

“…We also performed a semi-chronic study using the evaluation system described herein [17]. Future studies should focus on modi cation of the stimulation electrode array for STS and on chronic safety evaluation for longer than 48 weeks using the novel evaluation system.…”

Section: Resultsmentioning

confidence: 99%

Initial Evaluation of the Safety and Durability of Retinal Prostheses Based on Suprachoroidal–transretinal Stimulation using Bullet-shaped Platinum Electrodes

Tashiro

Kuwabara

et al. 2017

ABE

Self Cite

We have developed retinal prosthetic devices based on suprachoroidal-transretinal stimulation (STS). The effectiveness and safety of such novel devices are con rmed by in vitro and in vivo tests based on scienti c knowledge. Animal testing is especially important because it demonstrates the total safety of the device. We successfully developed a long-term evaluation system with automatic stimulation and measurement of electrochemical characteristics in freely moving rabbits. This system allows evaluation of long-term safety and change in electrochemical characteristics. In addition, we conducted a pilot evaluation of the safety of STS using bullet-shaped electrodes in rabbits. No obvious injuries were observed in all examinations. However, the array moved away from the retina in a few rabbits. Visual and electrical evoked potentials (EEPs) were recorded after three-month implantation. The function of the retinal neurons around the electrode is assumed to be maintained because EEPs were observed after three-month stimulation. However, the evoked potentials become indistinct with time in some rabbits. The development of implantable recording electrode capable of long-term evaluation is necessary for assessing the function of retina exposed to electrical stimulation. Long-term safety and change in electrochemical characteristics can be con rmed easily using this system. No histological difference was observed between the active and inactive electrodes, suggesting that the amount of charge used in the study can be safely injected. The charge injection capacity (CIC) of these electrodes provides an indication of the safety threshold for STS. The electrode array should have a curvature to t the eyeball to avoid movement of the array away from the retina. The electrode height is slightly greater compared to the sclera thickness. Accordingly, methods to enhance the CIC vs. geometrical surface area are required if the electrode height is reduced. We were able to obtain an indication of the required performance for the stimulation electrode based on the safe charge injection for STS (CIC of approximately 90 μC/cm 2 in PBS) and establish a system capable of evaluating safety and durability of retinal prostheses for long-term stimulation.

“…(8) In this study, one-month semichronic STS was applied to a rabbit retina, and its safety and efficacy were evaluated histologically, electrophysiologically, and electrochemically. Furthermore, to clarify the effectiveness of femtosecond laser-induced porosity (FLiP), (9) which has recently been introduced as a technique to improve the performance of stimulation electrodes, electrical stimulation was applied to both cohorts of smooth-surface electrodes without laser application and FLiP electrodes. A part of this study was presented at a conference.…”

Section: Introductionmentioning

confidence: 99%

Safety and Efficacy of Semichronic Suprachoroidal Transretinal Stimulation with Femtosecond Laser-induced Porosity and Smooth-surface Electrodes

Tashiro²,

Nakano

et al. 2018

Sensors and Materials

Self Cite

We have been developing a retinal prosthesis based on suprachoroidal transretinal stimulation (STS). From a practical viewpoint, it is essential to confirm the safety and effectiveness of continuous electrical stimulation to the retina. In this study, the electrical stimulation of a rabbit retina for 8 h a day was conducted for one month, and its safety and efficacy were evaluated by histological, electrophysiological, and electrochemical methods. Results suggested that one month of semichronic electrical stimulation by STS was safe and effective.