7.1  Introduction

One of the fundamental challenges for a visual prosthesis is to efficiently deliver visual stimuli from the external world to target neurons in the retina, optic nerve, or visual cortex. Power and visual information must be transmitted and subsequently distributed over an electrode array while ideally not interfering with residual vision, and keeping the natural association between visual information and eye movements. Four basic methods have been used to achieve this: direct wireline connection to implanted stimulators, radio frequency (RF) telemetry, serial optical telemetry, and parallel optical telemetry. In the first part of this chapter we review these techniques in their various incarnations.

After the data is received, providing the appropriate stimulus to the retina presents a new set of challenges: high-resolution prostheses require that nearby neurons are stimulated with high selectivity and broad dynamic range. While the electric field created by the electrode array and the constraints on cellular proximity have been characterized [35], the process of maintaining this proximity between electrodes and cells is less understood. Chronically preserving apposition between an epiretinal prosthesis and neurons requires only mechanical stabilization of the implant in the vitreous cavity. However, doing so with a subretinal prosthesis requires controlling the response of the retina to an implant. In the second part of this chapter we describe techniques used to mechanically stabilize implants, and the response of the retina to various implant geometries and coatings.

One of the critically important issues in development of retinal prosthesis is understanding the safe limits of electrical stimulation for prolonged periods of time.