John L. Wyatt

Minimally Invasive Retinal Prosthesis

A wireless retinal implant with a low-power area-efficient stimulator chip features an ASK demodulator, single-ended-to-differential converter, low-power DLL and programmable current drivers. The chip dissipates 1.3mW from plusmn2.5V at a data rate of 100kb/s. The chip is powered and driven through a wireless inductive link separated by 15mm

Ocular implants for the blind

Now in early development, an ultra-thin array of electrodes, powered by a laser and placed directly on surviving neurons of the retina, could provide usable percepts of light for the visually impaired.

Predicting the survival of patients with breast carcinoma using tumor size

Tumor size has long been recognized as the strongest predictor of the outcome of patients with invasive breast carcinoma, although it has not been settled whether the correlation between tumor size and the chance of death is independent of the method of detection, nor is it clear how tumor size at the time of treatment may be translated into a specific expectation of survival. In this report, the authors provide such a method.

REVIEW ■ : Prospects for a Visual Prosthesis

Diseases of the retina and optic nerve are common causes of irreversible blindness. Given the lack of effective treatments, several laboratories are utilizing microelectronic technology to develop either a cortical or retinal prosthesis. Each strategy offers certain advantages, but both face numerous and formidable chal lenges. Consequently, a clinically useful device of either type is still conceptual. The technological means to build prostheses are available, but the ultimate obstacle is the integration of the technology with the brain. This article reviews achievements of the ongoing efforts and focuses on our project to develop a retinal prosthesis. NEUROSCIENTIST 3:251-262, 1997

A method and technical equipment for an acute human trial to evaluate retinal implant technology

This paper reports on methods and technical equipment to investigate the epiretinal stimulation of the retina in blind human subjects in acute trials. Current is applied to the retina through a thin, flexible microcontact film (microelectrode array) with electrode diameters ranging from 50 to 360 microm. The film is mounted in a custom-designed surgical tool that is hand-held by the surgeon during stimulation. The eventual goal of the work is the development of a chronically implantable retinal prosthesis to restore a useful level of vision to patients who are blind with outer retinal degenerations, specifically retinitis pigmentosa and macular degeneration.

CMOS resistive fuses for image smoothing and segmentation

A two-terminal nonlinear element called a resistive fuse is described. Its application in image smoothing and segmentation is explained. Two types of CMOS resistive fuses were designed, fabricated, and tested. The first implementation employs four depletion-mode NMOS and PMOS transistors, occupying a minimum area of 30 mu m*38 mu m. The second implementation uses seven or 11 standard enhancement-mode transistors on an area of 75 mu m*100 mu m or less. Individual resistive-fuse circuits have been fabricated and tested and their functionality has been demonstrated. A one-dimensional network of 35 resistive fuses using the 11-transistor implementation was also fabricated in a standard CMOS process. Experimental results indicate that the network is capable of smoothing out small variations in image intensity while preserving the edges of objects. >

A Power-Efficient Neural Tissue Stimulator With Energy Recovery

This paper presents a power-efficient neural stimulator integrated circuit, designed to take advantage of our understanding of iridium-oxide electrode impedance. It efficiently creates a programmable set of voltage supplies directly from a secondary power telemetry coil, then switches the target electrode sequentially through the voltage steps. This sequence of voltages mimics the voltage of the electrode under the constant current drive, resulting in approximately constant current without the voltage drop of the more commonly used linear current source. This method sacrifices some precision, but drastically reduces the series losses seen in traditional current sources and attains power savings of 53%-66% compared to these designs. The proof-of-concept circuit consumes 125 μW per electrode and was fabricated in a 1.5-μm CMOS process, in a die area of 4.76 mm2.

A Hermetic Wireless Subretinal Neurostimulator for Vision Prostheses

A miniaturized, hermetically encased, wirelessly operated retinal prosthesis has been developed for preclinical studies in the Yucatan minipig, and includes several design improvements over our previously reported device. The prosthesis attaches conformally to the outside of the eye and electrically drives a microfabricated thin-film polyimide array of sputtered iridium oxide film electrodes. This array is implanted into the subretinal space using a customized ab externo surgical technique. The implanted device includes a hermetic titanium case containing a 15-channel stimulator chip and discrete circuit components. Feedthroughs in the case connect the stimulator chip to secondary power and data receiving coils on the eye and to the electrode array under the retina. Long-term in vitro pulse testing of the electrodes projected a lifetime consistent with typical devices in industry. The final assembly was tested in vitro to verify wireless operation of the system in physiological saline using a custom RF transmitter and primary coils. Stimulation pulse strength, duration, and frequency were programmed wirelessly from a Peripheral Component Interconnect eXtensions for Instrumentation (PXI) computer. Operation of the retinal implant has been verified in two pigs for up to five and a half months by detecting stimulus artifacts generated by the implanted device.

Mismatch sensitivity of a simultaneously latched CMOS sense amplifier

Derives a new formula for the sensitivity of a vertically matched CMOS sense amplifier, of the type used in dynamic-RAMs (DRAMs), to threshold voltage mismatch, parasitic capacitance mismatch, transconductance mismatch, and bit-line load capacitance mismatch. The formula yields insight into the DRAM sensing operation. The authors derive a sensitivity formula for this sensing scheme, using perturbation theory. The perturbation approach is rigorous: it avoids most approximations and ad-hoc assumptions, it introduces no free constants to be determined from simulations, and it yields an explicit closed-form solution. The formula agrees well with simulations. It is inherently slightly conservative and thus appropriate for use in design. >

Realization of a 15-channel, hermetically-encased wireless subretinal prosthesis for the blind

A miniaturized, hermetically-encased, wirelessly-operated retinal prosthesis has been developed for implantation and pre-clinical studies in Yucatan mini-pig animal models. The prosthesis conforms to the eye and drives a microfabricated polyimide stimulating electrode array with sputtered iridium oxide electrodes. This array is implanted in the subretinal space using a specially-designed ab externo surgical technique that affixes the bulk of the prosthesis to the surface of the sclera. The implanted device includes a hermetic titanium case containing a 15-channel stimulator chip and discrete power supply components. Feedthroughs from the case connect to secondary power- and data-receiving coils. In addition, long-term in vitro pulse testing was performed on the electrodes to ensure their stability for the long lifetime of the hermetic case. The final assembly was tested in vitro to verify wireless operation of the system in biological saline using a custom RF transmitter circuit and primary coils. Stimulation pulse strength, duration and frequency were programmed wirelessly using a custom graphical user interface. Operation of the retinal implant has been verified in vivo in one pig for more than three months by measuring stimulus artifacts on the eye surface using a contact lens electrode.