Development of a Wireless High-Frequency Microarray Implant for Retinal Stimulation - Artificial Sight: Basic Research, Biomedical Engineering, and Clinical Advances - page 170

Figure 9.1. Complete system of retinal prosthesis.
of different functional units of a retinal prosthesis is shown in Figure 9.2. In
extraocular unit, image from a camera is reduced to lower resolution by an image
processor, and transmitted after time multiplexing. In intraocular unit, a wireless
receiver recovers serial data of each pixel and sends them to the stimulator array
for further processing and stimulation. This chapter outlines the current research
and development of a retinal prothesis.
In general, to excite the retina the signal should be a biphasic current waveform
(Figure 9.3) [1]. There are four parameters associated with this waveform. They
are amplitude, width, interphase delay, and frequency. Amplitude represents
the gray level of the pixel, width and interphase delay depend on the degree
of a patient's retinal damage, while frequency is the frame rate. The charac-
teristics of these waveform parameters will depend on patient feedback on
visual perception. Typical values of the waveform reported in different papers
are: amplitude 10-600A, width 100s-2ms, delay 0-1ms, and frequency
10-125 Hz. The typical impedance of the retinal tissue is 10K for retinitis
pigmentosa (RP) and age-related macular degeneration (AMD) patient. However,
variations of stimulation waveforms such as high-frequency stimulation have
Figure 9.2. Block diagram of the retinal prosthesis.