Challenges in Realizing a Chronic High-Resolution Retinal Prosthesis - Artificial Sight: Basic Research, Biomedical Engineering, and Clinical Advances - page 130

Figure 7.1. System diagram of a chronic high-resolution retinal prosthesis.

a video-processing unit for transforming the video data to stimulation data
for the electrical pulses delivered to the retina. This data is sent through
a wireless link to avoid any penetrating wires that would cause discomfort,
open up the possibility of infection to the patient, and require frequent care
after the implantation. The stimulation data is received at the implant unit
by a data receiver. This data acts as an input to a stimulator that generates
the electrical pulses to the retina. A flexible cable transmits the electrical
outputs to an electrode array that interfaces the outputs of the stimulator to
the retina. All the electronics inside the eye receive power wirelessly, through
a power receiver unit. The electronics in the external unit operate from a
battery. In an ideal case, the stimulator, data recovery, and power recovery
units will be integrated into a single integrated circuit (IC) leading to a system-
on-chip (SoC). All the electronics have to be shielded from the biological
fluid inside the eye, and vice versa. This requires a hermetic, biocompatible
package that protects the electronics. Also, all the implant components inside
the eye such as coil, cable should be biocompatible for realizing a chronic
implant. The device should function safely and reliably for many years to
avoid frequent surgeries which would be needed if there are catastrophic
failures. The reliability of electronics refers to the breakdown of any device
due to constant stress over a long period of time. The breakdown of devices
can occur if the package fails and direct contact is made with biological

fluid.
The quality of vision restored through the retinal prosthesis is highly
dependent on the resolution of the image, which translates to the number
of stimulation sites on the retina. Simulations of prosthetic vision suggest
that 600-1000 electrodes will be required to restore visual function to