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Biomedical subjects

James D Weiland

Publications and source records attributed to James D Weiland.

At least 19 recordsLinked to original sources
PubMed2006

Electrical stimulation in normal and retinal degeneration (rd1) isolated mouse retina.

Stimulus threshold and response latencies were measured for electrically elicited retinal ganglion cell responses in retina isolated from the eyes of normal and retinal degenerate (rd1) mice. Stimulation of the ganglion cell-side in normal retina yielded a significantly lower mean threshold and shorter latency when compared with stimulation of the photoreceptor side in normal retina. The latency of the ganglion cell-side stimulation in normal retina also proved to be significantly shorter than the latency for stimulation of the ganglion cell side in rd1 retina. Thus both the electrode positioning as well as the health of the retinal tissue play a role in the stimulating current required to elicit a retinal response.

Animals↗
PubMed2006

Electrical stimulation in isolated rabbit retina.

Experiments were conducted to assess the effect of stimulating electrode parameters (size, position, and waveform shape) on electrically elicited ganglion cell action potentials from isolated rabbit retina. Thirty-eight isolated rabbit retinas were stimulated with bipolar stimulating electrodes (either 125 or 25 microm in diameter) positioned on either the ganglion or the photoreceptor side. Recording electrodes were placed between the optic disc and the stimulating electrodes. Cathodic-first, biphasic, current waveforms of varying pulse durations (0.1, 0.5, 1 ms) were used. For the four conditions tested (125-electrode and 25-microm electrode, ganglion cell, and photoreceptor positions) threshold currents ranged from 6.7 to 23.6 microA, depending on location and pulse duration. With 1-ms pulse duration, no statistically significant difference was seen between threshold currents when either size electrode was used to stimulate either the ganglion cell side or the photoreceptor side. For all groups, the threshold currents using the 1-ms pulse were lower than those using 0.1 ms, but the 0.1-ms pulses used less charge. These experiments provide a number of valuable insights into the relative effects of several stimulation parameters critical to the development of an implanted electronic retinal prosthesis.

Action Potentials↗
PubMed2006

Retinal prostheses for the blind.

INTRODUCTION: Using artificial means to treat extreme vision impairment has come closer to reality during the past few decades. The goal of this research has been to create an implantable medical device that provides useful vision for those patients who are left with no alternatives. Analogous to the cochlear implants for some forms of hearing loss, these devices could restore useful vision by converting visual information into patterns of electrical stimulation that excite the remaining viable inner retinal neurons in patients with retinitis pigmentosa or age-related macular degeneration. METHODS: Data for this review were selected through a comprehensive literature search. RESULTS: Advances in microtechnology have facilitated the development of a variety of prostheses that can be implanted in the visual cortex, around the optic nerve, or in the eye. Some of these approaches have shown the promise of providing useful visual input to patients with visual impairments. CONCLUSION: While the development of various retinal prostheses have shown promise in limited clinical trials, there are distinct advantages and disadvantages for each type of prosthesis. This review will focus primarily on the Epiretinal Intraocular Retinal Prosthesis, studied by our group, but will also briefly review other modalities: the subretinal prosthesis, cortical prosthesis, and optic nerve prosthesis.

Electric Stimulation Therapy↗
PubMed2005

Nanobiolistic delivery of indicators to the living mouse retina.

The development of a technique to load functional indicators into living neurons is an ongoing challenge in retinal neurophysiology. In a number of live-cell preparations, fluorescence-based indicators have been of particular importance for investigating ionic concentrations, protein localization, and other physiological parameters. In the present study, we demonstrate a novel technique that uses a modified gene gun to propel silver nanoparticles coated with indicators into live retinal neurons, and we highlight the advantages of using this technique to deliver these functional indicators.

Animals↗
PubMed2005

Implantation of an inactive epiretinal poly(dimethyl siloxane) electrode array in dogs.

The aim of this study is to investigate the long-term, mechanical biocompatibility of a polymer microtechnology that can be used to position electrodes in close proximity to the retina. Poly(dimethylsiloxane) (PDMS) arrays were manufactured by soft-lithography at Lawrence Livermore National Laboratory. The PDMS implant measured 4 mm x 40 mm x 55-60 microm and included 4-8 electrodes. Micromolded ribs were placed at the perimetry for strength and ease of manipulation. The PDMS arrays were implanted epiretinally in four normal dogs, with a single retinal tack used in each case to hold the device on the retina. The mechanical effects of the implant were followed up after surgical implantation by photography, fluorescein angiography, optical coherence tomography (OCT), and electrophysiologic tests. An intraoperative retinal tear occurred in the first implanted dog, causing retinal detachment and necessitating termination. The remaining dogs experienced no gross complications secondary to the array implantation procedure. During the follow-up period of 2 months in one eye and 6 months in three eyes, OCT demonstrated that the arrays were in close contact with the retina. Fluorescein angiography showed good perfusion of the retina under the array. At the end of 6 months, there was no statistical difference from baseline in mean retinal thickness under the array (P=0.43) or peripapillary retinal nerve fibre layer thickness corresponding to the implanted area (P=0.34). The mean distance between the array and the retinal surface varied from 32 to 68 microm throughout the follow-up. Histopathologic evaluation of the retinal implantation site in eyes followed for 6 months showed a general preservation of the normal, layered retinal structure, except for some localized retinal thinning in two eyes, where the array frame had been in direct retinal contact. The PDMS substrate micro array is a new and promising technology that can be scaled to support a high-density retinal stimulating array. Its implantation and handling is surgically manageable, and it forms a mechanically stable, acceptable interface with the inner retinal surface.

Animals↗
PubMed2005

Long-term stimulation by active epiretinal implants in normal and RCD1 dogs.

An epiretinal prosthesis, consisting of an extraocular microelectronic stimulator and an intraocular electrode array, was implanted in one eye of three blind and three sighted dogs. Three dogs (2 blind, 1 normal) were stimulated for 120 days, and two dogs (both normal) for 60 and 103 days respectively for 8-10 h/day at levels of 0.1 mC cm(-2) and 0.05 mC cm(-2), with each stimulus level presented to half of the array. One blind dog was kept as an inactive implant control. During the study period, electroretinograms (ERG) and fundus photographs were recorded. At the end of the study period, the dogs were sacrificed and histological and morphometric evaluation was made of the retina. No inflammatory reaction, neovascularization or hemorrhage was observed during the follow-up examinations. ERGs were unchanged. Stimulus levels used were of sufficient amplitude to elicit cortical evoked potentials. Histological evaluation showed no inflammatory infiltrates or changes in retina morphometry related to electrical stimulation when compared to the unstimulated control eye. Morphometric analysis revealed no consistent differences relating to electrical stimulation. In summary, chronic electrical stimulation of the dog retina at up to 0.1 mC cm(-2) with an epiretinal prosthesis does not appear to adversely affect the retina.

Animals↗
PubMed2005

Perceptual thresholds and electrode impedance in three retinal prosthesis subjects.

Three test subjects blind from retinitis pigmentosa were implanted with retinal prostheses as part of a FDA-approved clinical trial. The implant consisted of an extraocular unit that contained electronics for wireless data, power, and generation of stimulus current, and an intraocular unit that consisted of 16 platinum stimulating electrodes arranged in a 4 x 4 pattern within a silicone rubber substrate. The array was held to the retina by a small tack. The stimulator was connected to the array by a multiwire cable and was controlled by a computer based external system that allowed precise control over each electrode. Perception thresholds and electrode impedance were obtained on each electrode from the subjects over several months of testing. The electrode distance from the retina was determined from optical coherence tomography imaging of the array and retina. Across all subjects, average thresholds ranged from 24-702 microA (1-ms pulse). The data show that proximity to the retina played a role in determining the threshold and impedance, but only for electrodes that were greater than 0.5 mm from the retina.

Blindness↗
PubMed2005

Retinal prosthesis.

Retinal prostheses represent the best near-term hope for individuals with incurable, blinding diseases of the outer retina. On the basis of the electrical activation of nerves, prototype retinal prostheses have been tested in blind humans and have demonstrated the capability to elicit the sensation of light and to give test subjects the ability to detect motion. To improve the visual function in implant recipients, a more sophisticated device is required. Simulations suggest that 600-1000 pixels will be required to provide visual function such as face recognition and reading. State-of-the-art implantable stimulator technology cannot produce such a device, which mandates the advancement of the state of the art in areas such as analog microelectronics, wireless power and data transfer, packaging, and stimulating electrodes.

Animals↗
PubMed2003

Visual perception in a blind subject with a chronic microelectronic retinal prosthesis.

A retinal prosthesis was permanently implanted in the eye of a completely blind test subject. This report details the results from the first 10 weeks of testing with the implant subject. The implanted device included an extraocular case to hold electronics, an intraocular electrode array (platinum disks, 4 x 4 arrangement) designed to interface with the retina, and a cable to connect the electronics case to the electrode array. The subject was able to see perceptions of light (spots) on all 16 electrodes of the array. In addition, the subject was able to use a camera to detect the presence or absence of ambient light, to detect motion, and to recognize simple shapes.

Aged↗
PubMed2003

Visually guided performance of simple tasks using simulated prosthetic vision.

Loss of photoreceptor cells is one of the major causes of blindness. Several groups are exploring the functional replacement of photoreceptors by a retinal prosthesis. The goal of this study was to simulate the vision levels that recipients of retinal prostheses with 4 x 4, 6 x 10, and 16 x 16 electrode arrays may experience, and to test the functionality of this vision. A PC video camera captured images that were converted in real time into dots ("pixels"). The PC monitor and a head-mounted display worn by test subjects displayed the pixelized images. To assess performance of normally sighted individuals with each array, we designed a set of tasks including: four-choice orientation discrimination of a Sloan letter E, object recognition and discrimination, a cutting task, a pouring task, symbol recognition, and two reading tasks. In the letter E task, subjects were found to have visual acuities of 20/1,810, 20/1,330, and 20/420 with the 4 x 4, 6 x 10, and 16 x 16 arrays, respectively. Most subjects were able to read fonts as small as 36 point with the 16 x 16 array, corresponding with a visual acuity of 20/600 in our system. The test subjects partially overcame the visual limitation of the system by scanning the video camera over the letters allowing spatial and temporal integration of visual information. In all categories, subjects performed best with the 16 x 16 array and least well with the 4 x 4 array. Even with the lowest resolution array, however, some subjects could recognize simple objects and symbols.

Adult↗
PubMed2003

Advances in the development of visual prostheses.

Visual prostheses are based on neuronal electrical stimulation at different locations along the visual pathway (ie, cortical, optic nerve, epiretinal, subretinal). In terms of retinal prostheses, advances in microtechnology have allowed for the development of sophisticated, high-density integrated circuit devices that may be implanted either in the subretinal or epiretinal space. Analogous to the cochlear implants for some forms of deafness, these devices could restore useful vision by converting visual information into patterns of electrical stimulation that would excite the remaining spared inner retinal neurons in patients with diseases such as retinitis pigmentosa and age-related macular degeneration. The different types of implants and recent results are discussed, but special emphasis is given to retinal implants.

Electric Stimulation↗
PubMed2003

The value of preoperative tests in the selection of blind patients for a permanent microelectronic implant.

PURPOSE: To determine the best candidates (ie, those requiring lowest current levels delivered to the retina to elicit visual perceptions) for long-term implantation of a microelectronic retinal implant through a series of preoperative visual, psychophysical, and electrophysiological tests. METHODS: This study protocol was granted an investigational device exemption by the Food and Drug Administration and was approved by the institutional review board at the University of Southern California. After informed consent was obtained, all subjects underwent the following preoperative tests: dark-adapted bright flash and 30-Hz flicker electroretinograms, electrical evoked responses (EERs) using a Burian-Allen corneal electrode to stimulate the globe, and psychophysical tests to evaluate the light and electrically elicited visual perceptions. Intraocular stimulation (IOS) of the retina was performed by an array of electrodes positioned on the internal limiting lamina. RESULTS: Lower vision correlated with less sensitive psychophysical responses (P<.0001). Lower vision and less sensitive psychophysical tests correlated with higher EER values for stimulus pulse widths of 2 ms (P<.0008) and 4 ms (P<.0002). Lower IOS currents correlated with more sensitive psychophysical responses (P<.02) and lower EER values at 4 ms (P<.04). CONCLUSIONS: Preoperative testing, especially psychophysical and electrophysiological tests to assess light and electrically driven visual responses, can help in evaluating patients for suitability for receiving a permanent microelectronic retinal implant. Further study is warranted.

Blindness↗
PubMed2002

In vitro electrical properties for iridium oxide versus titanium nitride stimulating electrodes.

Stimulating electrode materials must be capable of supplying high-density electrical charge to effectively activate neural tissue. Platinum is the most commonly used material for neural stimulation. Two other materials have been considered: iridium oxide and titanium nitride. This study directly compared the electrical characteristics of iridium oxide and titanium nitride by fabricating silicon substrate probes that differed only in the material used to form the electrode. Electrochemical measurements indicated that iridium oxide had lower impedance and a higher charge storage capacity than titanium nitride, suggesting better performance as a stimulating electrode. Direct measurement of the electrode potential in response to a biphasic current pulse confirmed that iridium oxide uses less voltage to transfer the same amount of charge, therefore using less power. The charge injection limit for titanium nitride was 0.87 mC/cm2, contradicting other reports estimating that titanium nitride was capable of injecting 22 mC/cm2. Iridium oxide charge storage was 4 mC/cm2, which is comparable to other published values for iridium oxide. Electrode efficiency will lead to an overall more efficient and effective device.

Coated Materials, Biocompatible↗
PubMedDate not supplied

Comparison of electrical stimulation thresholds in normal and retinal degenerated mouse retina.

PURPOSE: To compare the threshold for electrically elicited action potentials of retinal ganglion cells in normal mouse retina and photoreceptor degenerated (rd) mouse retina. METHODS: Microelectrode recordings were made from retinal ganglion cells of normal and rd mice. Mice with a genetically based retinal degeneration (rd mice) were grown to the age of 16 weeks, when light-evoked responses could no longer be recorded. A bare wire was placed in the vitreous to stimulate the retina with charge-balanced current pulses. The following pulse shapes were investigated: single, square biphasic pulse, single sine wave, and biphasic pulse trains. RESULTS: Normal mice had significantly lower stimulus thresholds than rd mice for all pulse shapes. In normal and rd mice, short pulses were more efficient with respect to total charge used, but required a higher current. In normal mice, sine wave stimulation was significantly more efficient than a biphasic pulse of the same duration. No difference was noted between sine wave and square wave stimulation in rd mice. Pulse trains offered little benefit over single pulses. CONCLUSION: The amount of electrical charge required to elicit an action potential is dependent on the condition of the retina and the shape of the stimulus pulse used to deliver the charge.

Action Potentials↗
PubMedDate not supplied

Retinal prosthesis for the blind.

Most of current concepts for a visual prosthesis are based on neuronal electrical stimulation at different locations along the visual pathways within the central nervous system. The different designs of visual prostheses are named according to their locations (i.e., cortical, optic nerve, subretinal, and epiretinal). Visual loss caused by outer retinal degeneration in diseases such as retinitis pigmentosa or age-related macular degeneration can be reversed by electrical stimulation of the retina or the optic nerve (retinal or optic nerve prostheses, respectively). On the other hand, visual loss caused by inner or whole thickness retinal diseases, eye loss, optic nerve diseases (tumors, ischemia, inflammatory processes etc.), or diseases of the central nervous system (not including diseases of the primary and secondary visual cortices) can be reversed by a cortical visual prosthesis. The intent of this article is to provide an overview of current and future concepts of retinal and optic nerve prostheses. This article will begin with general considerations that are related to all or most of visual prostheses and then concentrate on the retinal and optic nerve designs. The authors believe that the field has grown beyond the scope of a single article so cortical prostheses will be described only because of their direct effect on the concept and technical development of the other prostheses, and this will be done in a more general and historic perspective.

Blindness↗