Hugo Haemmerle

Can subretinal microphotodiodes successfully replace degenerated photoreceptors

The idea of implanting microphotodiode arrays as visual prostheses has aroused controversy on its feasibility from the moment it appeared in print. We now present results which basically support the concept of replacing damaged photoreceptors with subretinally implanted stimulation devices. Network activity in degenerated rat retinae could be modulated through local electrical stimulation in vitro. We also investigated the long term stability and biocompatibility of the subretinal implants and their impact on retinal physiology in rats. Ganzfeld electroretinograms and histology showed no significant side effect of subretinal implants on retinal function or the architecture of the inner retina.

Electrical multisite stimulation of the isolated chicken retina.

Visual prostheses such as subretinal implants are intended for electrical multisite excitation of the retinal network. To investigate relevant issues like spatial resolution and operational range, we have developed an in vitro method using microelectrode arrays to stimulate isolated retinae. Ganglion cell activity in the chicken retina evoked by distally applied spatial voltage patterns consisted of fast bursts, transient inhibition and delayed discharges, and depended on the amount, location and spatial pattern of the injected charge. The response was altered or disappeared when synaptic transmission was blocked. Our results indicate that shape perception and object location can be partially achieved with subretinal electrical multisite stimulation.

The Development of Subretinal Microphotodiodes for Replacement of Degenerated Photoreceptors

There are presently several concepts to restore vision in blind or highly visually handicapped persons by implanting electronic devices into the eye in order to partially restore vision. Here, the approach to replace retinal photoreceptors by a subretinally implanted microphotodiode array (MPDA) is summarized. A survey is given on the present state of the development of MPDAs, the possibility of in vitro and in vivo tests as well as first results on biocompatibility and histology. Additionally, electrophysiological recordings in rabbits and rats are presented which have received such subretinal implants.

Subretinales Mikrophotodioden-Array als Ersatz für degenerierte Photorezeptoren?

ZusammenfassungEs wird eine Übersicht über den Stand der Entwicklungen eines subretinalen, elektronischen Mikrophotodioden-Arrays gegeben, mit dem degenerierte Photorezeptoren ersetzt werden können. Verschiedene Prototypen wurden entwickelt, getestet und bei verschiedenen Versuchstieren bis zur Dauer von 18 Monaten implantiert. Die Tatsache, dass mit subretinalen Elektroden elektrische Antworten vom visuellen Kortex von Schweinen abgeleitet werden können und Antworten auch in vitro in Netzhäuten von Ratten mit Netzhautdegenerationen nachweisbar sind, zeigt die Sinnhaftigkeit dieses Ansatzes. Allerdings sind noch wichtige Fragen der Biokompatibilität, der Langzeitstabilität und der Art des vermittelbaren Bildeindrucks zu bearbeiten, bevor an einen Einsatz beim Menschen zu denken ist.AbstractA survey is given on the status of developments, concerning a subretinal electronic microphotodiode array that aims at replacing degenerated photoreceptors. Various prototypes have been developed, tested, and implanted in various experimental animals up to 18 months. The fact that electrical responses were recorded from the visual cortex of pigs after electrical stimulation by subretinal electrodes and the fact that responses are also recorded in-vitro in degenerated rat retinae, shows the feasibility of this approach. However, there are a number of open questions concerning the biocompatibility, the long-time stability, and the type of transmitted image to be solved before application in patients can be considered.

Reply to the Letter of Drs. Chow and Peachey: The Subretinal Microphotodiode Array Retinal Prosthesis II

Accessible online at: http://BioMedNet.com/karger In response to our rebuttal-letter to the editor, Drs. Chow and Peachey state that our consortium neglects the original authorship and patent claims of Dr. Chow and coworkers. In our opinion this statement is wrong. We have cited the abstract of Dr. Chow [1], the only publication in a scientific journal available at that time from Dr. Chow on this topic, and therefore have informed the reader that he was the first who started to develop a subretinal microphotodiode array for retinal prosthesis. Patents which Dr. Chow wants us to quote are a claim of rights and are usually not cited in a scientific journal. It also should be kept in mind that the German Microphotodiode Array Project started in autumn 1995, as was published in our paper [2] and that very serious offers have been made to Dr. Chow to join the German MPD array consortium. Our major goal is to develop a subretinal implantable visual prosthesis for patients suffering from photoreceptor degeneration. Should a commercially available prosthesis be based on Dr. Chow’s ideas his patents will allow him to enforce his copyright to the extent it is applicable. We have lined out our viewpoints in a previous letter [3] in extenso. References