Chairperson: G. Richard GERMANY, S. Rizzo ITALY
16.00 | J. Rizzo USA
Attaining higher resolution visual prosthetics: a reviewview abstract- click here
Blindness is a major health problem and a common form of disability. In industrialized countries, the most common forms of blindness occur are the result of neural disease, most commonly of the outer retina. Retinitis pigmentosa (RP) is one such disease that produces a loss of peripheral then central vision. There is no treatment to restore lost vision for RP, though the field of molecular therapy now offers some optimism. Another approach to restoring lost vision for patients with RP is with a visual prosthesis, which is an artificial device that is designed to replace the function of damaged or lost visual neurons. Visual prosthetics are being developed for use within the eye and at more distal locations along the afferent visual pathway. The ultimate visual potential that might be realized with a prosthesis is often considered in terms of the number of stimulating channels, which is often discussed in terms of the number of electrodes that a system can support. For those devices that use a hard-wired approach to deliver electricity to the electrodes, the rate limiting step is the creation of a high density hermetic feedthrough assembly (through which pass wired connections between the stimulator chip and the electrode array). However, for any type of visual prosthetic devices (regardless of the architecture of the hardware), the ultimate challenge is the ability to electrically stimulate relatively small pockets of neurons to hopefully create a large number of visual “pixels” that can be differentiated by the patient and assembled into a coherent image. A major concern of devices with a large number of electrodes is the increased potential for “crosstalk” among the populations of neurons that are being driven, which would presumably degrade the visual image. Various approaches for enhancing the quality of the visual image will be discussed.
16.20 | M. Keserü GERMANY
Limitations of visual prosthetics view abstract- click here
Retinal implant technology has improved over the last years, gaining advantages and possibilities in visual rehabilitation for patients with retinal degenerative diseases. Several study groups have already reported of succesful promotion of visual sensations by electrical stimulation of the human visual system. Furthermore the use of visual prostheses seems to increase patency in daily life tasks for retinal degeneration patients. Nevertheless the anatomical, physiological and technical circumstances are setting boundaries for prosthetic visual restoration. Various factors have been identified, that influence the success of retinal stimulation. Aiming for larger electrode arrays and higher resolution of retinal implants, those factors have to be specially adressed. Reviewing the literature, we want to rule out the limitations of visual function by electrical retinal sitmulation regarding to the different techniques and sites of stimulation.
16.35 | S. Rizzo ITALY
Electrical stimulation of the retina: the second sight project view abstract- click here
The Argus II Retinal Prosthesis System is the first approved treatment for severe to profound outer retinal degeneration. In 2011 it has received CE Mark, and is now commercially available in Europe. More than 50 patients all around the word received one of the Second Sight prostheses.
With over 95 cumulative patient-years of follow-up on 30 subjects in the clinical trial, the Argus II success is the results of the largest study of a visual prosthesis to date.
All subjects implanted with a Second Sight Argus II implant had bare light perception or worse vision due to retinitis pigmentosa.
In this presentation we will prove the safety of the surgery and the system; we will substantiate the improvements in visual function and in activity of daily life that patients benefit after receiving the implant; we will show the extreme software potential of the device.
The rate of adverse events, which was moderate to begin with, has been further decreased in the second half of the subjects. As for implant stability 93% of the Argus II implanted devices are intact and functioning, patients can use them regularly at home.
Results on visual function tests with high-contrast stimuli showed a hierarchy of function, progressing from the ability to locate object, through the ability to detect direction of motion, and finally to the ability to distinguish the orientation of black and white gratings. To date, the best grating visual acuity measurement was 1.8 logMAR (20/1260). Functional vision O&M tests demonstrate that subjects are significantly better at performing visual tasks with the System ON vs. OFF and that this effect is maintained during long-term follow-up (i.e. >3years).
New software developments like the Acuboost™, the face recognition function, the colour stimulation, clearly evidence the great advantages that the image processing can give to patients.
These results confirm previous reports on the ability of the Argus II prosthesis to provide visual function and functional vision over the long-term. Higher resolution devices are in development.
16.50 | K. Stingl GERMANY
Subretinal prosthesis: Concept and clinical results view abstract- click here
In current multicentre clinical trial subretinal microelectronic implants Alpha IMS Implant (Retina Implant AG, Reutlingen, Germany) are applied in blind patients with hereditary degenerations of the outer retina. The active part of the subretinal implant consists of 1500 independent microphotodiode-amplifier-electrode units providing an electrical image for the bipolar cells and subtituting the essential photoreceptor function. Efficacy tests are repeated during up to twelve months trial and follow-up.
In nine patients enrolled in the first, monocenter part during 2010-2012, light perception, light localization, motion detection (angular speed up to 35 deg/s), grating acuity measurement (up to 3.3 cycles per degree) and visual acuity measurement with Landolt C-rings (up to 20/546, decimal 0.037) were possible. Identification, localization and discrimination of objects improved significantly with the implant (p<0.05 for each subtest). Three subjects were able to read letters spontaneously. Five subjects reported implant-mediated visual perceptions in daily life. With the current subretinal implant useful visual functions can be restored in blind patients.
17.05 | E. Fernandez SPAIN
A cortical visual neuroprosthesis: Technological developments and preliminary human studies view abstract- click here
We will introduce the CORTIVIS project, which aims to develop prototypes in the field of visual rehabilitation and demonstrate the feasibility of a cortical neuroprosthesis, interfaced with the visual cortex, as a means through which a limited but useful visual sense may be restored to profoundly blind people.
We will review some of the principles and difficulties related with all intracortical microelectrodes and the problems associated with selective recording and/or stimulation of specific groups of neurons. We will emphasize the role of neural plasticity in order to achieve the desired behavioural outcome and introduce a new bioinspired retina able to stimulate in real-time the cortical microelectrodes. We will also introduce a novel approach for 3D phosphene mapping that is reliable, accurate and can be used for standardized human testing. Finally we will discuss some of the exciting opportunities and challenges that lie in this intersection of neuroscience research, biomedical engineering and neuro-opthalmology.
17.20 | A. Antal GERMANY
Transcranial electrical stimulation: Clinical results view abstract- click here
In the last years, new stimulation techniques and protocols have been developed that alter visual functions not by induction of neuronal activity, but by modulation of spontaneous activity and excitability. One of these techniques is stimulation of the brain with direct current (transcranial direct current stimulation, tDCS). The primary mechanism of tDCS is thought to be a modulation of the resting membrane potential of targeted neurons. The polarity-dependent cortical activity and excitability increases by anodal stimulation or reductions by cathodal stimulation emerge during the stimulation, but – depending on the duration and the intensity of the application - can remain for hours after the end of the stimulation. Recent results show that anodal and cathodal stimulation can change the excitability of the visual areas and can modify visual perception. Furthermore, tDCS-induced neuroplastic changes in healthy subjects are in line with the observation of improved visual functions in patients e.g. after application of phosphene-generating current impulses. Nevertheless, whether tDCS has a positive impact on vision restoration in patients with damaged visual pathways is still an open question. Current studies have shown that the combination of occipital anodal tDCS with visual field rehabilitation appears to enhance visual functional outcomes compared with visual rehabilitation alone. However, the effects of stimulation show some heterogeneity and it will be important for future studies to reproduce previous results and to explore the factors influencing the beneficial effects of stimulation to a larger degree.
17.30 | B. Sabel GERMANY
Vision restoration after optic neuropathy using non-invasive alternating current stimulation view abstract- click here
Non-invasive electrical stimulation is known to induce cortical plasticity in normal subject. We now wished to learn if non-invasive, repetitive transorbital alternating current stimulation (rtACS) may also improve visual functions in patients with optic nerve damage.
In two prospective, randomized, sham-controlled clinical trials we studied patients that suffered optic nerve damage, including glaucoma cases. Patients were assigned to a group receiving rtACS or sham treatment with sub-clinical stimulation. rtACS was carried out for 10 consecutive days (20-40 min daily) using non-invasive AC-current bursts with amplitudes < 1000µA at 10-50Hz. The primary outcome measures were detection performance in visual field testing and acuity. In addition, patient reported vision related quality of life was measured with the NEI-VFQ questionnaire and EEG recordings were collected. Analysing the post-treatment minus baseline differences significant increases were observed in the primary outcome measures (perimetric stimulus detection rates) and several secondary measures, where rtACS significantly improved compared to sham in visual fields, reaction time, and in visual acuity. The increase of stimulus detection performance and acuity improvement remained constant at a 2-months follow-up in most but not all patients and it was associated with improvements vision related quality of life. Physiological EEG changes were noticed also: increased alpha-power in both occipital and frontal brain areas.
We propose that non-invasive electrical stimulation can improve visual fields in patients with visual field defects that are clinically relevant. Because of the EEG changes we propose that the treatment enhanced neuroplasticity in the brain, activating residual visual capacities by increased neuronal synchronization in higher visual (and non-visual) areas. Our results are compatible with the view that alternating current stimulation induces LTP-like strengthening of synaptic transmission in residual tissue, thus restores some of the lost vision in many (but not all) patients. Our findings confirm prior observations (Sabel et al., Nature med, 1998) that vision loss after optic nerve or brain damage must not be viewed as irreversible but that there is some room for optimism of vision improvement through mechanisms of brain plasticity.
17.40 | G. Anasstasiou GERMANY
Electrotherapy for dry age related macular degeneration view abstract- click here
Introduction: Dry AMD is a progressive disease which often ends up with a severe loss of vision. Dietary rules, nutrition supplements, and avoid of risk factors (e.g. smoking) may retard progression in some cases. Electrical stimulation has shown remarkable results on choroid vessels and retinal cell responses on experimental settings. Though no data on electrical stimulation and dry AMD exists, many companies offer devices for such treatment at home.
Patients and Methods: Prospective, placebo-controlled, case series (N = 22). Patients with dry AMD were treated twice a day for 5 consecutive days with a probe attached transpalpebral at 8 points around the eye globe (n = 12). Evaluation of the treatment was made at day 5, one month and finally 6 months after treatment. The placebo group (n = 10) underwent the same procedure but no current was applied (sham device).
Results: Electrical stimulation was well tolerated. No side effects were seen or were reported during the study. Visual acuity improved 4.6 and 5.7 EDTRS letters at 1 and 4 weeks, respectively. At final examination (6 months) a loss of 1.4 letters compared to the 4 weeks result was observed. The placebo group showed no changes (± 0.5 letter). Similar results were found by the evaluation of contrast sensitivity, whereas macular sensitivity measured by microperimetry showed no clear pattern of difference.
Conclusions: The potential benefit for the dry AMD patients and the low risk of the treatment are two major arguments for a future phase II study.
17.50 | A. Schatz GERMANY
Phosphene thresholds via transcorneal electrical stimulation in healthy subjects and patients with retinal diseases
18.00 | End of Session