Implants, Biocompatbility & Technology (IBT) Group

Team Leader: Prof. Walter

Team Members: Dr. Rößler, Dr. Hermel

Projects: The IBT Group is working on active and passive implants for ophthalmology. The group is developing implants for the eye in cooperation with industrial and academic partners. Currently the group is pursuing the following ideas:

Retina Implant
Intraocular pressure sensor

The idea of a Retina Implant is that in patients with retinal degeneration electrical stimulation of the retina may serve as a substitute for the degenerated neurons. In several studies it was shown that blind subjects suffering from retinitis pigmentosa have visual sensations when the retinal surface is stimulated by electric currents. Several concepts for Retinal Implants have been developed: subretinal implants, where the electrodes are placed underneath the retina and epiretinal implants, where the electrodes are placed onto the retinal surface. The IBT group is focussing on epiretinal implants. The members of the group are involved in the BMBF funded EPI-RET project since 1995. The IBT group also did clinical testings for IIP Technology.

EPI-RET Project

EPI-RET is a project funded by the German Minister for Research and Education since 1995. EPI-RET is now in its third stage of development facing the implantation of prototype devices in humans.

Results from EPI-RET phases I and II
Cooperation partners in PEI-RET phases I and II
Current results from EPI-RET phase III
Cooperation partners in PEI-RET phase III

System Concept and Summary of the Results of Phases I and II (1995 – 2004)

The main achievements of the EPI-RET project phases I and II were the development of the system concept and the fabrication of a first prototype of an implant featuring fill wireless control over stimulation paradigms on 25 platinum electrodes. Operating procedures haven been tested by the IBT group, e.g. our group showed that tack fixation of epiretinal devices was safe and sufficient to keep the implant close to the retinal surface. We were also able to show that electrical stimulation achieved specific cortical activation.

Figure right: Working principle of an epiretinal implant: The picture is captured by a camera placed into a spectacle frame. The camera signal is preprocessed and data together with energy is sent into the implant consisting of a receiver and a stimulator. The receiver unit is inserted into the capsular bag after removal of the lens. The microelectrode array is placed onto the retinal surface and fixated here with a retinal tack.
Fundus photographs of electrical inactive epiretinal microelectrode arrays placed onto the retinal surface and fixated with a retinal tack.
Histology of tack fixated epiretinal devices Was performed in the Institute of Pathology of the RWTH Aachen. The slides were achieved by grinding techniques.
Cortical potentials recorded from the rabbits cortex after epiretinal stimulation using an epiretinal microelectrode array placed onto the retina surface using heavy liquids after vitrectomy.
Recordings of intrinsic metabolic activity from the cat’s visual cortex after epiretinal electrical stimulation of the retina. Black areas are metabolic active areas with a higher oxygen consumption. These experiments were performed with Zoltan Kisvarday and Ulf Eysel in his lab at the Institute of Neurophysiology in Bochum University.

Project partners in phase I and II

University Bonn, Department of Computer Science, Prof. Dr. R. Eckmiller
Fraunhofer Institute for Mikrosystems, Prof. Dr. Hosticka, Prof. Dr. W. Mokwa
University Duisburg, Department of Optoelectronics, Prof. Dr. D. Jaeger
Fraunhofer Institute for Biomedical Engineering, Prof. Dr. J. U. Meyer
University Cologne, Department for Vitreoretinal Surgery, PD Dr. P. Walter
RWTH Aachen, Institute for Pathology, Prof. Dr. Ch. Mittermayer
University Essen, Eye Clinic, Prof. Dr. N. Bornfeld
University Marburg, Eye Clinic, PD Dr. L. Hesse
University Münster, Eye Clinic, Prof. Dr. H. Gerding
University Leipzig, Eye Clinic, Prof. Dr. P. Wiedemann
University Marburg, Department for Neurophysics, Prof. Dr. R. Eckhorn
University Bochum, Department for Neurophysiology, Prof. Dr. U. Eysel

Current results of EPI-RET phase III

The prototype device is currently fabricated and biocompatibility tests are planned.

Project partners in EPI-RET phase III

Fraunhofer Institute for Mikrosystems, Prof. Dr. Hosticka, Prof. Dr. W. Mokwa
RWTH Aachen, Department of Ophthalmology, Prof. Dr. P. Walter
RWTH Aachen, Institute for Neuropathology, Prof. Dr. J. Weis
University Essen, Eye Clinic, Prof. Dr. N. Bornfeld
University Marburg, Department for Neurophysics, Prof. Dr. R. Eckhorn
Bytec Stolberg
Dr. Schmidt Intraokularlinsen, St. Augustin
Thomas Recording Giessen

Contact: Dr. Gernot Roessler

EPI-FIX Project

The EPI-FIX Project is intended to develop an alternative fixation method based on surface modification of the implant and is funded by the IZKF Biomat - the Interdisciplinary Clinical Research Centre at the Medical Faculty of RWTH Aachen University.

Tack fixation of epiretinal devices is safe and with that technique a close contact between the electrodes and the retina is achieved. A tack is inserted through the retina and through the choroids. Its anchor is placed within the sclera. Removal of such a structure may be complicated and also electrical stimulation may be altered by the surgical trauma. Therefore we are looking for an alternative procedure to fixate an electrode array on the retinal surface using surface modification of the polyimide basis material. To achieve this goal we are working together with researchers from the Institute of Macromolecular Chemistry and colleagues from the Institute of Materials in Electrical Engineering. The project is performed within the research framework of the Interdisciplinary Centre for Clinical Research at the University Hospital of the RWTH Aachen (IZKF Biomat).

Pictures of pilot experiments on biological fixation. Devices were stabilized using heavy liquids, glial elements were seen after tackless fixation and cells growing through pores in a device could be identified:

Cooperation partners within the IZKF Biomat and the RWTH Aachen University:
Professor Dr. D. Klee, Institute of Macromolecular Chemistry
Professor Dr. W. Mokwa, Dr. K. Hungar, Institute for Materials in Electrical Engineering

Contact: Dr. Gernot Roessler

IIP project

The company IIP Technology in Bonn is developing an epiretinal implant. Together with retina specialists in Vienna, Essen, and Hamburg a clinical trial was performed to evaluate stimulation parameters in blind subjects suffering from Retinitis pigmentosa. Surgery was performed in 20 subjects. The experiences in the five subjects operated on in Aachen showed that in four subjects visual percepts could be elicited. In one patient being blind for 30 years no visual percept could be induced. Complications were not seen in the patients operated by the IBT group in Aachen.

Cooperation partners:
IIP Technology, Bonn, Germany
Department of Ophthalmology, University Essen, Prof. Dr. N. Bornfeld, PD Dr. T. Laube
Department of Ophthalmology, University Hamburg, Prof. Dr. Richard
Department of Ophthalmology, University Vienna, Dr. M. Velikay-Parel

Contact: Dr. Rössler

Selected publications on the Retina Implant Project:

Walter P, Mokwa W. Epiretinal visual prostheses. Ophthalmologe. 2005 Oct;102(10):933-40.
Walter P. Electronic visual prostheses. Klin Monatsbl Augenheilkd. 2005 Jun;222(6):471-9.
Hornig R, Laube T, Walter P, Velikay-Parel M, Bornfeld N, Feucht M, Akguel H, Rossler G, Alteheld N, Lutke Notarp D, Wyatt J, Richard G. A method and technical equipment for an acute human trial to evaluate retinal implant technology. J Neural Eng. 2005 Mar;2(1):S129-34.
Walter P, Kisvarday ZF, Gortz M, Alteheld N, Rossler G, Stieglitz T, Eysel UT. Cortical activation via an implanted wireless retinal prosthesis. Invest Ophthalmol Vis Sci. 2005 May;46(5):1780-5.
Alteheld N, Roessler G, Vobig M, Walter P. The retina implant--new approach to a visual prosthesis. Biomed Tech (Berl). 2004 Apr;49(4):99-103.
Alteheld N, Vobig MA, Marzella G, Berk H, Shojaei R, Heimann U, Held S, Walter P, Bartz-Schmidt KU. Biocompatibility tests on the intraocular vision aid IOVA. Biomed Tech (Berl). 2002;47 Suppl 1 Pt 1:176-8.
Walter P. Medical aspects of active implants in the eye. Biomed Tech (Berl). 2002;47 Suppl 1 Pt 1:158-60.
Walter P, Heimann K. Evoked cortical potentials after electrical stimulation of the inner retina in rabbits. Graefes Arch Clin Exp Ophthalmol. 2000 Apr;238(4):315-8.
Walter P, Szurman P, Vobig M, Berk H, Ludtke-Handjery HC, Richter H, Mittermayer C, Heimann K, Sellhaus B. Successful long-term implantation of electrically inactive epiretinal microelectrode arrays in rabbits. Retina. 1999;19(6):546-52.

Links

Intraocular pressure sensor

The role of the intraocular pressure in the disease process of glaucoma is currently under debate. It is clear that the intraocular pressure is the main risk factor in the genesis of the glaucomatous optic neuropathy. Although this is the case, our management of glaucoma included only rare measurements of the intraocular pressure (IOP). Determination of IOP depends on the office hours of the eye doctor although IOP shows considerable variation. External measurements showed potential uncertainties, e.g. depending on corneal thickness. Measurements under real life conditions are completely missing. It is desirable to monitor IOP continuously similar to the determination of the arterial blood pressure what has significantly improved the management of arterial hypertension. The idea of this project is to fabricate an implant which measures IOP and sends the data to a receiver outside the eye. The implant does not need any battery because it is loaded with energy via an inductive link from the external receiver station.

Working principle of an implantable IOP monitor integrated into an artificial intraocular lens with pressure and temperature sensors and wireless control.
Prototype of the intraocular lens with an integrated pressure and temperature sensor, AD converter, and HF transponder for wireless control and data exchange. The lens is foldable. Implantation is possible through a 6 mm incision.
Comparison between Tonopen® measurements and the IOPS system in a rabbit.

Cooperation partners:

Acritec GmbH, Henningsdorf, Germany
Mesotec GmbH, Hannover, Germany
Bytec GmbH, Stolberg, Germany

Contact: Dr. Nils Alteheld

Selected publications on the IOPS project

Walter P. Medical aspects of active implants in the eye. Biomed Tech (Berl). 2002;47 Suppl 1 Pt 1:158-60.
Walter P. Intraocular pressure sensor: where are we - where will we go? Graefes Arch Clin Exp Ophthalmol. 2002 May;240(5):335-6.
Walter P, Schnakenberg U, vom Bogel G, Ruokonen P, Kruger C, Dinslage S, Ludtke Handjery HC, Richter H, Mokwa W, Diestelhorst M, Krieglstein GK. Development of a completely encapsulated intraocular pressure sensor. Ophthalmic Res. 2000 Nov-Dec;32(6):278-84.