Efficacy of suprachoroidal-transretinal stimulation in a rabbit model of retinal degeneration.
ABSTRACT Purpose. To develop a middle-sized animal model of outer retinal degeneration and to evaluate the effectiveness of suprachoroidal-transretinal stimulation (STS) in eliciting cortical potentials from this model. Methods. Twelve rabbits were intravenously injected with 0.47 mg/kg verteporfin and the retinas were irradiated with a red light for 90 minutes. Fluorescein angiography and full-field and focal electroretinography (ERG) were performed at 7 and 28 days after the irradiation. Electrically evoked potentials (EEPs) were elicited by electrical stimulation, with the STS electrode implanted over the irradiated region, 1 month and 1 year after the irradiation. EEPs were also recorded from three rabbits before and after retinotomy of the normal retina surrounding the degenerated area, to eliminate the influence of stray currents. The retina beneath the site of the STS electrode was examined histologically at 1 month (group 1) and 1 year (group 2) after the irradiation. Results. An extensive area of degeneration was detected histologically, mainly in the outer retina after the irradiation. Focal ERGs were not recorded when the stimulus was confined to the irradiated area; however, EEPs were successfully elicited by STS of the same area 1 month and 1 year after the irradiation. The 360 degrees retinectomy did not significantly alter the amplitudes, the implicit times, or the thresholds of EEPs evoked by STS. Conclusions. Verteporfin with light irradiation induces degeneration predominantly in the outer retinal layers in rabbits. The elicitation of EEPs by STS from the degenerated area suggests that the STS system may be useful in patients with retinitis pigmentosa.
- [show abstract] [hide abstract]
ABSTRACT: Teflon-coated platinum-iridium wires are placed in the vitreous as electrodes in artificial vision systems. The purpose of this study was to determine whether these wires have toxicity in the vitreous cavity, and to examine the durability of their coating when grasped by forceps. Rabbits were implanted with platinum-iridium wires that were 50 μm in diameter and coated with Teflon to a total diameter of 68 or 100 μm. To examine the biocompatibility, electroretinograms (ERGs) and fluorescein angiography (FA) were performed before and 1 week, 1, 3, and 6 months after the implantation of the electrode. After 6 months, the eyes were histologically examined with light microscopy. To check the durability, the surface of a coated wire was examined with scanning electron microscopy after grasping with different types of forceps. At all times after the implantation the amplitudes and implicit times of the ERGs recorded were not significantly different from those recorded before the implantation (P > 0.05). FA showed no notable change during the follow-up periods. Histological studies showed that the retinas were intact after 6 months of implantation. There was no damage to the Teflon-coated wire after grasping the wire with forceps with silicon-coated tips, while surface damage of the Teflon that did not extend to the platinum-iridium wire was found when grasped by vitreoretinal forceps. We conclude that Teflon-coated platinum-iridium wire is highly biocompatible in the vitreous for at least 6 months. Wires should be handled with vitreoretinal forceps with silicone-coated tips in order to avoid causing damage during wire manipulation.Journal of Artificial Organs 07/2011; 14(4):357-63. · 1.41 Impact Factor
- [show abstract] [hide abstract]
ABSTRACT: PURPOSE: To characterize electrically elicited visual evoked potentials (eVEPs) in Argus II retinal implant wearers. METHODS: eVEPs were recorded in four subjects and analyzed by determining amplitude and latency of the first two positive peaks (P1 and P2). Subjects provided subjective feedback by rating the brightness and size of the phosphenes. We established eVEP input-output relationships, eVEP variability between and within subjects, the effect of stimulating different areas of the retina, and the maximal pulse rate to reliably record eVEPs. RESULTS: eVEP waveforms had low signal-to-noise ratios, requiring long recording times and substantial signal processing. Waveforms varied between subjects, but showed good reproducibility and consistent parameter dependence within subjects. P2 amplitude was overall the most robust outcome measure and proved an accurate indicator of subjective threshold. Peak latencies showed small within-subject variability, yet their correlation with stimulus level and subjective rating were more variable than that of peak amplitudes. Pulse rates of up to (2)/3 Hz resulted in reliable eVEP recordings. Perceived phosphene brightness declined over time, as reflected in P1 amplitude, but not in P2 amplitude or peak latencies. Stimulating-electrode location significantly affected P1 and P2 amplitude and latency, but not subjective percepts. CONCLUSIONS: While recording times and signal processing are more demanding than for standard VEP recordings, the eVEP has proven to be a reliable tool to verify retinal implant functionality. eVEPs correlated with various stimulus parameters and with perceptual ratings. In view of these findings, eVEPs may become an important tool in functional investigations of retinal prostheses.Investigative ophthalmology & visual science 04/2013; · 3.43 Impact Factor
- [show abstract] [hide abstract]
ABSTRACT: Purpose: The photosensitive polyimide film, Durimide, is a common component of retinal prostheses; however, retinal cell response to Durimide has not been effectively studied This work assessed the in vitro biocompatibility of a retinal prosthesis containing platinum-electrode embedded Durimide film. Materials and methods: Biocompatibility evaluation assessed cytotoxicity, attachment, and proliferation of two cell lines: a human retinal pigmented epithelium cell line (CRL) and a rhesus monkey choroid- retinal endothelial cell line (RF/6A). Cells were cultured with the platinum-electrode embedded Durimide film, with tissue-culture treated polystyrene plates (TCPS) used as a control substrate for cell growth. The effect of a Durimide-exposed medium on cell apoptosis and life cycle was assessed using flow cytometry (FCM). Results: The indirect cytotoxicity evaluation revealed no toxic effect of the prosthesis on cells. The attachment and proliferation of CRL and RF/6A cells cultured with the Durimide prostheses showed no significant differences to the control. The FCM experiments demonstrated a liquid medium exposed to the prosthesis had no effects on apoptosis or cell life cycle in comparison with the control (p > 0.05). Conclusions: The results demonstrate that Durimide has good biocompatibility with retinal cell lines CRL and RF/6A. In conclusion, while further in vitro and in vivo studies are required to clarify long-term effects, Durimide is indicated as a promising material with suitable biocompatibility for retinal implants.Current eye research 07/2012; 37(11):1036-44. · 1.51 Impact Factor