D. Yanai

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 /spl times/ 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 /spl mu/A (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.

Factors Affecting Perceptual Thresholds in Epiretinal Prostheses

PURPOSE The goal was to evaluate how perceptual thresholds are related to electrode impedance, electrode size, the distance of electrodes from the retinal surface, and retinal thickness in six subjects blind as a result of retinitis pigmentosa, who received epiretinal prostheses implanted monocularly as part of a U.S. Food and Drug Administration (FDA)-approved clinical trial. METHODS The implant consisted of an extraocular unit containing electronics for wireless data, power recovery, and generation of stimulus current, and an intraocular unit containing 16 platinum stimulating electrodes (260- or 520-microm diameter) arranged in a 4 x 4 pattern. The electrode array was held onto the retina by a small tack. Stimulation was controlled by a computer-based external system that allowed independent control over each electrode. Perceptual thresholds (the current necessary to see a percept on 79% of trials) and impedance were measured for each electrode on a biweekly basis. The distance of electrodes from the retinal surface and retinal thickness were measured by optical coherence tomography on a less regular basis. RESULTS Stimulation thresholds for detecting phosphenes correlated with the distance of the electrodes from the retinal surface, but not with electrode size, electrode impedance, or retinal thickness. CONCLUSIONS Maintaining close proximity between the electrode array and the retinal surface is critical in developing a successful retinal implant. With the development of chronic electrode arrays that are stable and flush on the retinal surface, it is likely that the influence of other factors such as electrode size, retinal degeneration, and subject age will become more apparent. (ClinicalTrials.gov number, NCT00279500.).

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.

Visual task performance in blind humans with retinal prosthetic implants

A prototype electronic retinal prosthesis has been tested in three subjects. The system features an implanted retinal stimulator and an external system for image acquisition, processing, and telemetry. The subjects in general performed better than chance on psychophysical tests involving object detection, object counting, object discrimination, and direction of movement.

Electrical stimulation of retina in blind humans

A prototype electronic retinal prosthesis has been tested in two subjects. The system features an implanted retinal stimulator and an external system for image acquisition, processing, and telemetry. Subjects can perceive light when each of the 16 electrodes were activated. Stimulus thresholds ranged from 28 to 1417 /spl mu/A. Strength duration curves were obtained in all two subjects. Dynamic range for the brightness of the stimulus was demonstrated. Using the camera, the subjects were able to locate objects and determine the direction of movement.

Effect of oxygenated intraocular irrigation solutions on the electroretinogram after vitrectomy.

Purpose: To investigate the effect of oxygenated intraocular irrigating solutions on electroretinograms (ERGs) for postvitrectomy rabbits. Methods: Eight groups of five rabbits each underwent pars plana vitrectomy on the right eye; the left eye of each rabbit served as control. The intraocular irrigating solutions were balanced salt solution (BSS), BSS-plus, BSS + oxygen (BSS + O2), BSS-plus + O2, and combinations of each with the addition of endoillumination (L). All animals were evaluated by single-flash scotopic electroretinography on the operated and nonoperated eyes before surgery and at 1 hour, 1 day, 1 week, and 1 month after surgery by an unmasked observer. The main outcome measures were dark-adapted b-wave amplitudes of operated eye/nonoperated eye ratios. The results for the different groups were compared by analysis of variance. Results: Mean dark-adapted b-wave amplitudes of operated eye/nonoperated eye ratios ± SD for BSS-plus and BSS-plus + O2 before surgery and 1 hour, 1 day, 1 week, and 1 month after surgery were 1.01 ± 0.09, 0.50 ± 0.11, 0.95 ± 0.11, 0.97 ± 0.11, and 0.99 ± 0.08 and 0.98 ± 0.08, 0.59 ± 0.10, 0.92 ± 0.06, 0.97 ± 0.08, and 0.97 ± 0.10, respectively. At both 1 hour and 1 day after surgery, rabbits treated with BSS-plus + O2 had an earlier b-wave return to baseline findings, but the differences were not statistically significant (P > 0.05). Mean dark-adapted b-wave amplitudes of operated eye/nonoperated eye ratios ± SD for BSS and BSS + O2 before surgery and 1 hour, 1 day, 1 week, and 1 month after surgery were 1.02 ± 0.10, 0.47 ± 0.09, 0.77 ± 0.07, 0.89 ± 0.07, and 0.89 ± 0.07 and 1.02 ± 0.06, 0.62 ± 0.16, 0.94 ± 0.09, 0.97 ± 0.08, and 0.96 ± 0.06, respectively. One hour and 1 day after surgery, ERG readings for rabbits treated with BSS + O2 exhibited a statistically significantly earlier return of ERG voltage to baseline values compared with both BSS and BSS + L (P = 0.05 and P = 0.02, respectively). One day after surgery, rabbits treated with BSS alone had the lowest ERG ratios. One week and 1 month after surgery, for all solutions tested other than BSS, ERG values were within normal limits. Conclusion: The use of oxygenated solutions appears to affect ERG readings after pars plana vitrectomy. Further studies to evaluate the role of oxygenated solutions in different vitreoretinal surgical procedures are warranted.

Clinical results with the model 1IRP implant

This paper discuss the feasibility study of implanting an epiretinal prosthesis in humans with bare or no light perception vision from retinitis pigmentosa. Patients were implanted with a Second Sight intraocular epiretinal prosthesis in the eye with worse vision. The implant consisted of an extraocular microelectronic device and an intraocular electrode array, connected by a multiwire cable. At the end of the procedure, it was concluded that all the subjects could see visual perceptions that correlate to electrical stimulus from a chronically implanted retinal prosthesis. Patients used a camera driven stimulus to perform simple tasks.