Efficacy of Suprachoroidal-Transretinal Stimulation in a Rabbit Model of Retinal Degeneration
Department of Ophthalmology, Osaka University Graduate School of Medicine, Suita, Japan.Investigative ophthalmology & visual science (Impact Factor: 3.4). 11/2009; 51(4):2263-8. DOI: 10.1167/iovs.09-4120
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.
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ABSTRACT: Electrical stimulation of retinal neurons has been shown to be a feasible way to elicit visual percepts in patients blind from retinal degenerations. The EPIRET3 retinal implant is the first completely wireless intraocular implant for epiretinal stimulation. Stimulation tests have been performed during a clinical trial that was carried out at the eye clinics of Aachen and Essen to evaluate the safety and the efficacy of the implant. Six legally blind retinitis pigmentosa patients were included in the study. In accordance with the regulations laid down in the study protocol, three 1-hour perceptual tests for each subject were performed within 4 weeks of surgery. Stimuli were charge-balanced square current pulses of various durations and current amplitudes. All subjects reported visual percepts as a result of electrical stimulation by the implant. Thresholds for eliciting visual percepts varied between them but were below the safety limits of electrical stimulation. Stimulation success depended stronger on pulse duration than on current amplitude or total charge delivered. Subjects were able to discriminate between stimulation patterns of different orientations or at different locations of the electrode array. The EPIRET3 system is suitable to elicit visual percepts in blind retinitis pigmentosa patients.
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ABSTRACT: Up until now there has been no available treatment for diseases causing the permanent impairment of retinal photoreceptors. Currently the development of the retinal prostheses is the earliest to promise a result that can be implemented in the clinical treatment of these patients. Implants with different operating principles and in various stages of progress are presented in details, highlighting the characteristics, as well as the Hungarian aspects of the development. This survey intends to provide an overview on retinal prostheses, implantable in case of degenerative diseases of the retina, by reviewing and assessing the papers published in relevant journals and based on personal experience. Developments in microelectronics in recent years made it possible and proved to be feasible to replace the degenerated elements in the retina with electrical stimulation. Multiple comparable approaches are running simultaneously. Two types of these implants are directly stimulating the remaining living cells in the retina. Hitherto the finest resolution has been achieved with the subretinal implants. Although the epiretinal implant offer lower resolution, but requires shorter surgery for implantation. Retinal implants in certain retinal diseases are proved to be capable of generating vision-like experiences. A number of types of retinal implants can be expected to appear in clinical practice a few years after the successful conclusion of clinical trials.
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ABSTRACT: To investigate the feasibility of implanting a newly developed suprachoroidal-transretinal stimulation (STS) prosthesis in dogs and to determine its biocompatibility and stability over a 3-month period. The STS prosthesis system consisted of an array of 49 electrodes (nine were active), an intravitreal return electrode, and an extraocular microstimulator. The 49-electrode array was implanted into a scleral pocket of each of three healthy beagle dogs. Color fundus photography, fluorescein angiography, electroretinography, and functional testing of the STS system were performed postoperatively. The dogs were euthanatized 3 months after the implantation, and the retinas were evaluated histologically. All the prostheses were successfully implanted without complications, and no serious complications occurred during the 3-month postoperative period. The fixation of the implant was stable throughout the experimental period. Fluorescein angiography showed that the entire retina, including the area on the electrode array, remained well perfused without intraocular inflammation. Electroretinograms recorded from the eyes with the prosthesis did not differ significantly from those recorded from control eyes. Functional testing of the STS system showed that this system performed well for the 3-month experimental period. Histologic evaluations showed good preservation of the retina over the electrode array. Implantation of a newly developed STS retinal prosthesis into a scleral pocket of beagle dogs is surgically feasible and can be performed without significant damage to the retina or the animal. The biocompatibility and stability of the system were good for the 3-month observation period.
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