34a. Update on artificial vision
Mark Humayun (Los Angeles)
A retinal prosthesis has the potential to treat blinding diseases of the outer retina, such as agerelated
macular degeneration and retinitis pigmentosa. Although photoreceptors are significantly
degenerated by these diseases, the inner retinal cells are still present and can be electrically
activated to produce the sensation of light. An on-going clinical trial is evaluating a lowresolution
retinal prosthesis while technology to support higher resolution systems is under
development. In the clinical trial, prototype epiretinal prostheses were implanted in six subjects
with bare or no light perception due to retinitis pigmentosa. The FDA granted an investigational
device exemption and USC institutional review board approved the study protocol.
Subjects were screened using visual psychophysics, electrophysiology, ophthalmic photography,
and scanning laser ophthalmoscopy. Implants consist of an extraocular microelectronic
device and an intraocular electrode array, connected by a multiwire cable. The electrode array
is a 4x4 grid of platinum electrodes embedded in silicone rubber. Electrodes are wirelessly activated using an external system.
The external system is controlled via a computer interface or a head mounted video camera. To date, 6 subjects have
been implanted for 29-57 months. Perception thresholds of less than 20 microAmperes (1 millisec pulses) have been routinely
recorded on multiple electrodes. Performance using the head mounted video camera suggests that subjects are capable
of interpreting patterned electrical stimulation. Subjects can identify objects from a set and detect the direction of a moving
bar. Using data generated by the clinical trial, considerable progress has been made towards a higher resolution device.
The high-resolution system is targeting 1000 electrodes, which simulations predict can restore face recognition and mobility
to blind individuals. An image processing system has been realized that is capable of real-time implementation of image
decimation and filtering (for example, edge detection). Application specific integrated circuits (ASICs) have been designed
and tested to demonstrate closed loop power control, data telemetry, and efficient microstimulation. A dual-band telemetry
system has been developed that separates power and data transmission to allow the optimization of these functions.
Parylene substrate microfabrication technology is being used to simultaneously form a power coil, data coil, interconnects,
and stimulating electrodes..