Ralf Hornig

University Medical Center Hamburg - Eppendorf, Hamburg, Hamburg, Germany

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Publications (24)37.03 Total impact

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    ABSTRACT: Purpose: As part of a clinical trial, an investigational epiretinal implant (IMI Intelligent Medical Implant) was implanted in a retinitis pigmentosa patient. The prosthesis was wirelessly controlled by a visual interface containing a microcamera, providing wireless data and energy transmission. Forty-nine (49) electrodes were used for pattern recognition. This study examined the changes of perceptual thresholds over time and its relation to long-term stimulation. The goal of the study was to introduce stimulus-related depression of perceptual threshold (StirDepth) measurements as a method to gain further insight into the safety profile of electrical stimulation. Methods: The perceptual threshold was defined as the level of stimulation intensity at which a phosphene perception with a probability of 50% was detected using the Best-PEST method. StirDepth was measured by comparing the threshold changes immediately before and after a stimulation session of using three active electrodes and one passive electrode, which served as control. Results: The initial threshold of the day remained stable over the observed period. In StirDepth measurement all thresholds raised significantly after the stimulation sessions. The threshold increase of the active electrodes never exceeded that of the inactive control electrode. Conclusions: StirDepth measurement is feasible in epiretinal implants. The prolonged stimulation raised no safety concerns in the patient. The threshold increase of both the active electrodes and the control electrode leads one to hypothesise that cognitive or neurophysiological effects are the cause rather than the desensitizing of the retinal network or incipient retinal damage.
    Acta ophthalmologica 09/2013; · 2.44 Impact Factor
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    ABSTRACT: This paper presents an integrated neural stimulator with highly efficient and flexible frontend which is intended for an epiretinal implant with 1024 electrodes. It features programmable stimulation pulse shapes, a high-voltage (HV) output driver with compliance monitor for supply voltage adaptation, active and passive charge balancers, and electrode impedance measurement. Area and power efficiency is achieved by global timing assignment and local amplitude control over a bus at the local stimulation units. Major power savings in the distributed digital control units are realized by implementing global and local clock gating. Two stimulator frontends have been fabricated in a 0.35 $\mu\hbox{m}$ HVCMOS process. Each frontend features four demultiplexed outputs and consumes 0.2 ${\hbox{mm}}^{2}$ core area. A maximum voltage compliance of 20 V is achieved and up to 1 mA of output current can be adjusted with up to 50 dB dynamic range. In vitro experimental results performed on a platinum black electrode in 0.9% saline solution are given.
    IEEE Journal of Solid-State Circuits 01/2012; 47:244-256. · 3.06 Impact Factor
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    ABSTRACT: To determine the threshold charges needed for eliciting visual perceptions through acute electrical stimulation of the human retina in patients suffering from retinitis pigmentosa, using an epiretinal microelectrode array. In a multicentre study, 20 patients (average age 55 years) with visual acuities ranging from 4/200 to no light perception were included. The stimulation procedure was performed during a pars plana vitrectomy, for a maximum of 45 min, by using a microcontact film with IrO(x) electrodes connected by cable to a current generator. After repeated stimulation and threshold charge determination, the microelectrode array was removed. Nineteen of 20 patients stated in the postoperative interviews that they experienced one or more visual perceptions with close time correlation to single stimulation events. Minimum threshold charges needed to generate visual perceptions could be measured and verified in 15 patients. The charge level ranged from 20 to 768 nC with single or multiple electrodes. One patient suffered a retinal detachment during the procedure; this patient's retina was successfully reattached. There were no further adverse reactions observed during the 3-month follow-up. Acute epiretinal stimulation of the human retina, using a microelectrode array, can elicit visual perceptions in blind patients with retinitis pigmentosa.
    Acta ophthalmologica 11/2011; 90(1):e1-8. · 2.44 Impact Factor
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    ABSTRACT: Degenerative retinal diseases like retinitis pigmentosa and age-related macular degeneration are among the most common causes of blindness worldwide. Electronic visual prostheses represent a potential therapeutic option of increasing importance in otherwise incurably impaired patients. Based on extensive animal experiments, several devices are now being tested in clinical trials. According to the placement of the electrodes, possible stimulation sites are located subretinally, epiretinally, along the optic nerve or cortically. Anatomical, physiological and pathophysiological aspects must be considered in development and clinical application. To provide an appropriate retinal substitute, the optimal integration and adaptation of the prosthesis into the highly complex system of the visual pathway is important. This article aims to summarize the relevant studies and provides an overview of the current status of developments and challenges that still need to be mastered.
    Ophthalmologica 02/2011; 225(4):187-92. · 1.41 Impact Factor
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    ABSTRACT: Purpose Epiretinal prostheses are developed to enhance the orientation of low vision patients and consequently their mobility. However to document visual progress repeated testing is necessary to eliminate learning effects. For this purpose we developed the Graz Mobility Test (GMT) and evaluated its suitability in low vision patients with retinitis pigmentosa. Aim of this study was to investigate the relation of visual function parameters and walking behavior of patients.Methods Low vision patients (n=16) with visual acuity (VA) ranging from light perception to 1.0 logMAR passed through a mobility test consisting of four different, structurally similar mazes with black obstacles. Each test was completed four to six times. A people tracking system and a specially designed computer program recorded head movements and the patient´s walking path. In addition passage time and number of contacts were recorded. VA was tested with the Modified Grating Test (MGT) and visual field (VF) was examined with the Goldmann perimeter.Results The subjects were divided into groups according to their VA. Patients with eccentric fields in general proved to have fewer contacts (mean: 3,4 contacts) due to their early detection of peripheral obstacles than those with less peripheral perception (mean: 9,7 contacs). Patients with better VA required less time and less head movements to pass the maze.Conclusion Recordings and measurement of visual function and formation into groups allowed us evaluation of individual coping strategies. Hence potential benefits of epiretinal prostheses could be evaluated by comparing pre- and postoperative values.
    Acta ophthalmologica 09/2010; 88(s246). · 2.44 Impact Factor
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    ABSTRACT: Purpose Despite the recent progress of retinal implants the effects of continuing stimulation still remains an open issue. Sofar the established safety limits are based on laboratory findings and clinical observations.This study examined the changes of perceptual threshold over time and its relation to longterm stimulation. The goal of the study was to establish stimulus induced depression of neuronal excitability (SIDNE) measurements as a method to gain further insight on the safety profile of epiretinal implants.Methods As part of a clinical trial a prototype of an epiretinal implant ( IMI Intelligent medical implant) with 61 active platinum electrodes was implanted in a retinitis pigmentosa (RP) patient. The threshold was defined as the level of stimulation intensity at which the patient had a visual perception in a defined probability of 50% using the Best-PEST method. SIDNE is measured by comparing the thresholds of two electrodes obtained at the beginning and at the end of a stimulation session. One electrode is actively used during the stimulation, the other remains passive. The stimulation is regarded as safe when the threshold raise of active electrodes is not significantly higher than of the inactive electrode.Results The threshold remained stable over the observation period. The threshold raise of the active electrodes never exceeded that of the inactive electrode.Conclusion SIDNE measurement is feasible in epiretinal implants. After prolonged stimulation the thresholds may increase by more than 16 % due to the patients fading concentration, however the stimulation was performed within the safety limits.
    Acta ophthalmologica 09/2010; 88(s246). · 2.44 Impact Factor
  • Acta ophthalmologica 11/2009; 88(7):e285-6. · 2.44 Impact Factor
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    ABSTRACT: The implantation of electronic retina stimulators appears to be a future possibility to restore vision, at least partially in patients with retinal degeneration. The idea of such visual prostheses is not new but due to the general technical progress it has become more likely that a functioning implant will be on the market soon. Visual prosthesis may be integrated in the visual system in various places. Thus there are subretinal and epiretinal implants, as well as implants that are connected directly to the optic nerve or the visual cortex. The epiretinal approach is the most promising at the moment, but the problem of appropriate modulation of the image information is unsolved so far. This will be necessary to provide a interpretable visual information to the brain. The present article summarises the concepts and includes some latest information from recent conferences.
    Klinische Monatsblätter für Augenheilkunde 04/2009; 226(3):149-53. · 0.70 Impact Factor
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    ABSTRACT: Purpose The Modified Grating Test is a newly designed test for visual acuity (VA) measurement in patients with retinitis pigmentosa (RP) with low vision. Freiburg Visual Acuity Test (FrACT) is a validated test for low vision, but no patients with RP were tested. In our study we tested RP patients investigating the consistency of the Modified Grating Test by comparing the results with those of the FrACT and the ETDRS charts.Methods 16 eyes of 8 patients were tested and divided into 3 groups depending on their VA. Group 1 had a VA of hand motion (HM, n= 6), group 2 counting fingers (CF, n=6) and group 3 better than CF (n=4). The Modified Grating Test consists of a circle with black and white bars of the same width in a decreasing logarithmic order covering the range from 2.7 to 0.3 logMAR. The FrACT is a computerized test with Landoldt C in different directions and in decreasing order. ETDRS charts were used at a distance of 0.5m. Each test was performed 4-5 times. The data were normally distributed. To compare the values we used the paired samples t-test.Results The mean VA in group 1 as measured by the Modified Grating Test was 1.3 logMAR and by FrACT 1.21 logMAR (p=0.21). In the group 2 the patients reached a mean VA of 0.7 logMAR with the Modified Grating Test and 0.6 logMAR with FrACT. 0.68 logMAR was measured with ETDRS charts (p=0.13).Conclusion Our preliminary data suggest that the Modified Grating Test is a suitable test for the low vision range and might be beneficial for the follow up in patients undergoing a retinal prosthesis implantation.
    Acta ophthalmologica 01/2009; 87:0-0. · 2.44 Impact Factor
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    ABSTRACT: Purpose Proliferative vitreoretinopathy (PVR) is known a known complication of implantation of epiretinal prostheses in porcine eyes using our combined surgical procedure of vitrectomy, lensectomy, large scleral incision and retinal tack insertion. The aim of the present experimental study is to investigate the intraocular reaction to particular parts of the epiretinal prostheses implantation procedure in pigs.Methods 15 pigs were divided into 3 groups. Group 1 (n=6) underwent vitrectomy, lensectomy, insertion of inactive epiretinal prosthesis through a scleral incision and fixation to the posterior pole with a retinal tack. In group 2 (n=5) vitrectomy, scleral incision and retinal tack insertion were performed. Group 3 (n=4) received vitrectomy, scleral incision and insertion of a shortened prosthesis into the vitreous cavity. The follow up was 4 weeks.Results PVR was observed in all eyes of group 1 and in one eye of the group 3 with unintentional perforation of the lens capsule by the shortened implant. In all other eyes funduscopy revealed no clinical pathology.Conclusion Our results indicate that lensectomy is the key stimulus for PVR in porcine eyes while other steps of the implantation procedure are well tolerated. Though pigs do not seem to be a reactive animal model, lens manipulation should be avoided in the surgical procedure for the implantation of retinal prostheses.
    Acta ophthalmologica 01/2009; 87:0-0. · 2.44 Impact Factor
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    ABSTRACT: Purpose To report on the first 4 months experience of a patient with the active IRIS- Implant.Methods 4 weeks after implantation the training with the active implant started. Thresholds were measured at each training day. Light perception, light localisation, point to point discrimination and motion detection were measured with special test procedures. Visual function training was performed.Results Visual perception was achieved, when the stimuli were generated by the computer and with the camera mode. All tests were successful.Conclusion Successful stimulation and major improvements during the training demonstrates that with the Iris Implant System a visual perception can be achieved, which is relevant for daily life.
    Acta ophthalmologica 01/2009; 87:0-0. · 2.44 Impact Factor
  • Klinische Monatsblatter Fur Augenheilkunde - KLIN MONATSBL AUGENHEILK. 01/2009; 226(03):149-153.
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    ABSTRACT: Purpose In epiretinal prosthesis surgery the fixation of the implant on the retina is generally performed with retinal tacks in order to achieve a firm and a sufficiently close attachment to the ganglion cells. However, this fixation does not allow the removal of the implant without potentially causing major trauma. We therefore developed a new fixation method for the implant with the goal of enabling a safe and less traumatic explantation procedure.Methods We implanted an inactive epiretinal device consisting of a polyimide strip and a calotte in 11 Göttinger minipigs. The concept of the new fixation method is to implant the tack first and fixate the implant on the tack with a silicone tube by using a special instrument developed for this purpose. Thus the implant is firmly attached to the retina and removal can be performed by simply splitting the silicone tube and lifting the implant from the tack while the tack remains in place.Results All animals were implanted successfully without major complications. At the end of the observation periods the retinal tack and the silicone tube fixating the implant on the tack were still in position. The explantation procedure was accomplished easily and without any complications.Conclusion This new implantation method ensures a firm fixation of the implant whilst also allowing explantation without trauma to the posterior eye segment.
    Acta ophthalmologica 01/2008; 86:0-0. · 2.44 Impact Factor
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    ABSTRACT: Purpose We created a visual function test, the Graz mobility (GM) test to document visual progress in artificial vision. In previous studies our low vision test adequately graded the low vision of patients with retinitis pigmentosa (RP). However in repeated testing the learning effect could contaminate the visual results after implantation. The aim of this study was to investigate the constancy of the performance and to record behavioural changes in repeated testing in low vision RP patients.Methods 8 low vision RP-patients with a visual acuity from hand motion to 20/800 were tested repeatedly in 1, 2, 3 and 6 months time intervals. The GM test consisted of four different, structurally similar mazes with 11 obstacles. The subjects passed through each course several times. A people tracking system with an integrated trajectory projection system was established to record horizontal and vertical scanning movements of people during the test. Passage time, walking speed, number of contacts, frequency of scanning movements and average scanning angle were recorded.Results In repeated testing significant changes of the passage time were observed once the patients became familiar with the mobility test. The maximum learning effect was achieved within the first test session and was never exceeded in the following sessions. However further changes in the remaining parameters were observed in each patient, displaying behavioural changes correlating to the level of comfort during the task performance.Conclusion The GM proves to be reliable for repeated testing in low vision patients and the learning effect will not contaminate the results of visual function changes. Furthermore behavioural changes can be objectively assessed.
    Acta ophthalmologica 01/2008; 86:0-0. · 2.44 Impact Factor
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    09/2007: pages 111-128;
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    ABSTRACT: The study investigates the utility of a newly designed mobility test for repeated testing of visual function in patients with severe visual impairment and future application in evaluating functional progress in patients with artificial vision. Ten subjects divided into three groups based on visual acuity (VA) ranging from light perception to 20/200 and reduced visual field (VF) were included in the study. The mobility test consisted of using a set of four different but structurally similar and relatively short mazes having a constant number of obstacles of various sizes. The subjects, divided into three groups by acuity, passed through each course several times. In general, the patients with better VA had a larger extent of VF. Average speed and number of contacts were recorded as measures of performance. The average passing times of the groups through the courses were significantly different (p = 0.03), which was influenced by VA and VF. There was no significant difference in average number of contacts between the groups (p = 0.15). The mobility test proved to be appropriate for gaining statistically relevant results in repeated individual testing of patients with severe vision impairment. Results show promise for use this mobility test as a tool for assessing visual function of patients undergoing implantation of a visual prosthesis for artificial vision.
    Journal of Neural Engineering 04/2007; 4(1):S102-7. · 3.28 Impact Factor
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    ABSTRACT: Seit der ersten elektrischen Stimulationen der Netzhaut von erblindeten Patienten vor ca. 10 Jahren, wurde weltweit die Erforschung und Entwicklung von retinalen Implantaten rasch vorangetrieben. Es entstanden viele Arbeitsgruppen, die verschiedene Ansätze der retinalen Implantate verfolgen. Beim epiretinalen Ansatz wird das Implantat auf der Netzhaut fixiert, um so die Ganglienzellen elektrisch zu stimulieren. Um einem physiologischen Stimulus so nahe wie möglich zu kommen, wird die digitale Bildinformation bearbeitet und reduziert. Diese wird dann in elektrische Informationen übersetzt und so in das Auge gesendet. Beim subretinalen Ansatz hingegen, werden Mikrophotodioden unter der Netzhaut positioniert. Dort transformieren die Mikrophotodioden das Licht direkt in elektrische Energie und stimulieren so die Netzhaut. Erste Implantationen an blinden Patienten mit Retinopathia pigmentosa sind schon erfolgt. Es konnten mit epiretinalen Implantaten bereits Lichtempfindungen hervorgerufen werden. Nach einem speziellen Training konnte der Patient die Lichtpunkte lokalisieren. Subretinale Implantate wurden ebenfalls beim Menschen eingesetzt, aber die Mikrophotodioden konnten nicht genug Energie generieren, um die Netzhaut zu stimulieren. Aus diesem Grund wurden in Folge Stromverstärker in das Implantat integriert. Ergebnisse nach diesen Implantationen werden noch erwartet. Auch von unserer epiretinalen Arbeitsgruppe um IIP-Technologies wurden erste Patienten schon implantiert, die Implantate wurden in den meisten Fällen gut vertragen und es wurde ein Fortschritt der blinden Patienten dokumentiert. Es ist anzunehmen, dass mit den Implantaten eine orientierende Sehschärfe erlangt werden kann. Das Ausmaß der Sehverbesserung wird auch von der Lernfähigkeit des Gehirns abhängen, das lernen muss, diese neuen Reize in eine sinnvolle Information umzusetzen. Since the first electrical stimulation of the retina in humans approximately 10 years ago, worldwide intensive research for the development of such retinal implants has been performed. Many research groups formed and developed different approaches. The epiretinal implant is fixed onto the retina and stimulates the ganglial cells electrically. In order to create a stimulus, which is as close as possible to physiological stimuli, the digital image-information is transformed and reduced. This information is then translated in electrical information and sent into the eye. In subretinal implants, however, microphotodiodes are positioned under the retina. These microphotodiodes transform the light into electrical energy and stimulate the retina. First implantations with epiretinal implants have already been performed in blind patients due to retinopathia pigmentosa. Light perception was achieved. After several sessions of an adequate training, the patients were able to localize light spots. Subretinal implants were also implanted in humans but microphotodiodes could not generate enough energy to stimulate the retina. For that reason an amplifier was integrated into the implant. However results after these implantations are not available up to now. Our working group around IIP-Technologies implanted patients with the first wireless epiretinal implants. The implants were tolerated well and point to point discrimination and pattern recognition could be achieved. It can be assumed that retinal implants will provide the patient with enough information to perform more complex tasks like orientation. Further levels of visual perception will also depend on the learning capabilities of the brain, which has to learn to transform these new stimuli into meaningful information.
    Spektrum der Augenheilkunde 01/2006; 20(5):211-214. · 0.18 Impact Factor
  • Spektrum Der Augenheilkunde - SPEKTRUM AUGENHEILKD. 01/2006; 20(4):180-184.
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    ABSTRACT: Degenerations of the outer retina in retinal diseases such as retinitis pigmentosa lead to blindness due to photoreceptor loss. A therapeutic option for visual rehabilitation is presently not available. Over the last few years, a retinal prosthesis has been developed and its use has been tested in animal experiments as well as in humans. With the epiretinal implant images of the environment are taken by a camera, these data are transmitted to an intraocular encoder, and the retina is electrically stimulated by a retinal stimulator placed epiretinally. The stimulation electrodes are placed as flexible microcontact electrodes by pars plana vitrectomy in an epimacular position. The threshold is determined by stimulations of increasing amplitudes. Initial results of acute epiretinal stimulation using an epiretinal implant in legally blind patients demonstrate that acute epiretinal stimulation of the human retina is feasible and safe.
    Der Ophthalmologe 08/2005; 102(7):688-91. · 0.53 Impact Factor
  • Ref. No: WO2005068014(A1), Year: 07/2005

Publication Stats

121 Citations
37.03 Total Impact Points

Institutions

  • 2013
    • University Medical Center Hamburg - Eppendorf
      • Department of Ophthalmology
      Hamburg, Hamburg, Germany
  • 2005–2011
    • University of Hamburg
      • Department of Ophthalmology
      Hamburg, Hamburg, Germany
  • 2001
    • University of Bonn
      • Institute for Computer Sciences
      Bonn, North Rhine-Westphalia, Germany