A Suprachoroidal Electrical Retinal Stimulator Design for Long‐Term Animal Experiments and In Vivo Assessment of Its Feasibility and Biocompatibility in Rabbits

Abstract

This article reports on a retinal stimulation system for long-term use in animal electrical stimulation experiments. The presented system consisted of an implantable stimulator which provided continuous electrical stimulation, and an external component which provided preset stimulation patterns and power to the implanted stimulator via a paired radio frequency (RF) coil. A rechargeable internal battery and a parameter memory component were introduced to the implanted retinal stimulator. As a result, the external component was not necessary during the stimulation mode. The inductive coil pair was used to pass the parameter data and to recharge the battery. A switch circuit was used to separate the stimulation mode from the battery recharging mode. The implantable stimulator was implemented with IC chips and the electronics, except for the stimulation electrodes, were hermetically packaged in a biocompatible metal case. A polyimide-based gold electrode array was used. Surgical implantation into rabbits was performed to verify the functionality and safety of this newly designed system. The electrodes were implanted in the suprachoroidal space. Evoked cortical potentials were recorded during electrical stimulation of the retina. Long-term follow-up using OCT showed no chorioretinal abnormality after implantation of the electrodes.

Current Steering in Retinal Stimulation via a Quasimonopolar Stimulation Paradigm

“…23 Monopolar and hexapolar (128.5 6 11.4 lC cm À2 ) results are within the range of studies by Wong et al 31 (184 lC cm…”

“…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.…”

“…23,25,27 With the increase in electrode numbers and density, the complex electric field interactions between stimulation electrodes will affect the ability to elicit discrete phosphenes using monopolar stimulation. [28][29][30] An alternative electrode configuration was proposed.…”

Electrically Evoked Responses in the Rabbit Cortex Induced by Current Steering With Penetrating Optic Nerve Electrodes

“…There are various types of visual prostheses, and according to the locations that are stimulated, they can be generally divided into the following categories: epiretinal, 1,3,[19][20][21][22] subretinal, 2,8,13,[23][24][25] suprachoroidal, 4,15,26,27 intrapapillary, 28 extraocular, 12 thalamic, 7 cortical, 6,10,11 and optic nerve (ON). 5,14 Among them, the ON approach may potentially achieve artificial vision over a relatively large area of the visual field.…”

Electronic restoration of vision in those with photoreceptor degenerations

“…Most surgical techniques for these implants involve slipping an electrode array between these layers, which protects the retina from any manipulation. 24,[60][61][62] Additionally, it may be easier to anchor these implants into the sclera for long-term stability and it may also be possible to implant multiple arrays, allowing vision across a greater extent of the visual field. The implants are located further from target neurons and in animal models require higher levels of current to generate cortical responses than an implant located subretinally.…”