Evaluation of phosphenes elicited by extraocular stimulation in normals and by suprachoroidal-transretinal stimulation in patients with retinitis pigmentosa.
ABSTRACT To determine the efficient parameters to evoke electrical phosphenes is essential for the development of a retinal prosthesis. We studied the efficient parameters in normal subjects and investigated if suprachoroidal-transretinal stimulation (STS) is effective in patients with advanced retinitis pigmentosa (RP) using these efficient parameters.
The amplitude of pupillary reflex (PR) evoked by transcorneal electrical stimulation (TcES) was determined at different frequencies in eight normal subjects. The relationship between localized phosphenes elicited by transscleral electrical stimulation (TsES) and the pulse parameters was also examined in six normal subjects. The phosphenes evoked by STS were examined in two patients with RP with bare light perception. Biphasic pulses (cathodic first, duration: 0.5 or 1.0 ms, frequency: 20 Hz) were applied through selected channel(s). The size and shape of the phosphenes perceived by the patients were recorded.
The maximum PR was evoked by TcES with a frequency of 20 Hz. The brightest phosphene was elicited by TsES with a pulse train of more than 10 pulses, duration of 0.5-1.0 ms and a frequency of 20 to 50 Hz. In RP patients, localized phosphenes were elicited with a current of 0.3-0.5 mA (0.5 ms) in patient 1 and 0.4 mA (1.0 ms) in patient 2. Two isolated or dumbbell-shaped phosphenes were perceived when the stimulus was delivered through two adjacent channels.
Biphasic pulse trains (> or =10 pulses) with a duration of 0.5-1.0 ms and a frequency of 20-50 Hz were efficient for evoking phosphenes by localized extraocular stimulation in normal subjects. With these parameters, STS is a feasible method to use with a retinal prosthesis even in advanced stages of RPs.
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ABSTRACT: Our goal was to determine the feasibility of using electrochemically treated bulk platinum electrodes with large charge injection capacity for a retinal prosthesis. Seven eyes of seven cats were studied. Small retinal areas were focally stimulated with electrochemically treated bulk electrodes (φ = 500 µm) placed in a scleral pocket. Fundus images with near-infrared (800-880 nm) light were recorded, and a 2D map of the reflectance changes elicited by the electrical currents was constructed by subtracting the images taken before stimulation from those taken after stimulation. The impedance of each electrode was measured at 1 kHz. The degree of retinal elevation by the electrode was measured by optical coherence tomography. Scleral thickness where the electrode array was inserted was measured in histologic sections. The diameter of reflectance changes (full width at half maximum) was 0.42 ± 0.22 mm [mean ± standard deviation (SD)] in minor axes and 1.46 ± 0.82 mm in major axes. The threshold current decreased with a reduction in the residual scleral thickness (R (2) = 0.9215; P = 0.0002); it also decreased with an increase in retinal elevation (R (2) = 0.6259; P = 0.0111).The threshold current also decreased with an increase in electrode impedance (R (2) = 0.2554; P = 0.0147). Electrochemically treated porous platinum electrodes can stimulate localized retinal areas. The threshold current necessary to stimulate the retina was influenced by residual scleral thickness and the electrode tightness of fit against the sclera.Japanese Journal of Ophthalmology 05/2014; · 1.27 Impact Factor
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ABSTRACT: Transcorneal electrical stimulation (TES) activates retinal neurons leading to visual sensations. How the retinal cells are activated by TES has not been definitively determined. Investigating the reflectance changes of the retina is an established technique and has been used to determine the mechanism of retinal activation. The purpose of this study was to evaluate the reflectance changes elicited by TES in cat eyes. Eight eyes of Eight cats were studied under general anesthesia. Biphasic electrical pulses were delivered transcornealy. The fundus images observed with near-infrared light (800-880 nm) were recorded every 25 ms for 26 s. To improve the signal-to-noise ratio, the images of 10 consecutive recordings were averaged. Two-dimensional topographic maps of the reflective changes were constructed by subtracting images before from those after the TES. The effects of different stimulus parameters, e.g., current intensity, pulse duration, frequency, and stimulus duration, on the reflective changes were studied. Our results showed that after TES, the reflective changes appeared on the retinal vessels and optic disc. The intensity of reflectance changes increased as the current intensity, pulse duration, and stimulation duration increased (P<0.05 for all). The maximum intensity of the reflective change was obtained when the stimulus frequency was 20 Hz. The time course of the reflectance changes was also altered by the stimulation parameters. The response started earlier and returned to the baseline later with higher current intensities, longer pulse durations, but the time of the peak of the response was not changed. These results showed that the reflective changes were due to the activation of retinal neurons by TES and might involve the vascular changes induced by an activation of the retinal neurons.PLoS ONE 01/2014; 9(3):e92186. · 3.73 Impact Factor
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ABSTRACT: PURPOSE: To report an improvement of the visual acuity after transcorneal electrical stimulation (TES) in a case of Best vitelliform macular dystrophy (BVMD). PATIENT AND METHODS: A 26-year-old woman diagnosed with BVMD presented with reduced vision. Her best corrected visual acuity (BCVA) was reduced to 20/200 in the right eye, and TES was performed once a month for two sessions. The current of the biphasic pulses (anodic first; duration, 10 msec; frequency, 20 Hz) was delivered using a DTL-electrode, and the duration of the TES was 30 min. RESULTS: The BCVA in the right eye slowly improved after the TES, and 6 months later the BCVA was 20/25. The results of Humphrey visual field tests (VF) and multifocal ERGs (mfERGs) were only slightly changed. Two years later, the BCVA decreased, and it was improved again after another session of TES with the same parameters of the electrical pulses. CONCLUSION: The improvement of the visual acuity in our case of BVMD indicates that TES should be tried in other cases of retinal dystrophy. Further clinical and laboratory studies on TES are needed.Albrecht von Graæes Archiv für Ophthalmologie 04/2013; · 1.93 Impact Factor