Elements of a visual neuroprosthesis

In order for a visual neuroprosthesis to become an accepted therapeutic approach to sight restoration, it is clear that those who will utilize this technology must realize that they will not be receiving sight like those with normal vision. It is also clear that a clinically acceptable system must be virtually invisible. This means that the components must be integrated into normal systems typically worn by individuals such as eyeglasses and an external package not much larger than a pocket organizer. While such invisibility would be the eventual goal of a commercial system, first-generation experimental systems are not expected to be so constrained.

Figure 11.5 Schematic representation of the elements of a visual neuroprosthesis. With the exception of retinal neuroprostheses, all of the devices reviewed in this chapter consist of the items illustrated. Retinal devices, due to their location, might not require telemetry and use very simplistic signal-processing and stimulator electronics. Further, these devices derive their power from ambient light. The video encoder essentially replicates the function of the photoreceptors, that is, transforming the visual signal into an electrical signal. The signal-processing electronics perform necessary filtering and remapping. As external electronics cannot be as efficient as the biology, which has been tuned through millions of years of evolution, external power may be necessary. The stimulator electronics convert the video signals into electrical signals that more effectively stimulate neurons. The interface to the neurons is provided by an array of electrodes.

Figure 11.5 Schematic representation of the elements of a visual neuroprosthesis. With the exception of retinal neuroprostheses, all of the devices reviewed in this chapter consist of the items illustrated. Retinal devices, due to their location, might not require telemetry and use very simplistic signal-processing and stimulator electronics. Further, these devices derive their power from ambient light. The video encoder essentially replicates the function of the photoreceptors, that is, transforming the visual signal into an electrical signal. The signal-processing electronics perform necessary filtering and remapping. As external electronics cannot be as efficient as the biology, which has been tuned through millions of years of evolution, external power may be necessary. The stimulator electronics convert the video signals into electrical signals that more effectively stimulate neurons. The interface to the neurons is provided by an array of electrodes.

A visual neuroprosthesis will be a complex system containing a number of interconnected elements. A block diagram of the elements that a visual prosthesis will likely contain is shown in Figure 11.5. It must contain the following components: a video encoder to capture the visual field in front of the user of the system, signal-processing electronics to transform the video image into a set of discrete signals that can be used to control the injection of current through the neural interface, some mechanism by which these processed signals and electrical power can be delivered in a wireless fashion to the implanted neural interface, stimulator electronic circuitry to control the currents injected through each electrode in the neural interface, and the neural interface that evokes the neuronal excitation. As this minimum set of components will be present in some form in a retinal, optic nerve, or a cortical visual prosthesis, we will expand upon these elements in the following sections.

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