Retinale und kortikale Aktivierung durch elektrische Stimulation mit Netzhautimplantaten

Zusammenfassung

In Deutschland leiden etwa 30 000–40 000 Menschen an der Krankheit Retinitis pigmentosa (RP), die im Endstadium zur Erblindung führt. Die bisher einzige Hilfe für an RP erblindete Patienten sind Netzhautimplantate, die seit mehreren Jahren entwickelt werden und nunmehr als Medizinprodukt zugelassen sind. Netzhautimplantate erzeugen durch elektrische Stimulation der degenerierten Netzhaut Sehwahrnehmungen, die im Alltag blinder Menschen hilfreich sind. Allerdings ist die gegenwärtig erreichbare Sehqualität noch so, dass die Menschen auch mit Implantat gesetzlich blind sind. Die Sehqualität, die mit epi- und subretinalen Implantaten erreicht werden kann, hängt zum einen von patientenindividuellen Faktoren ab, wie etwa dem individuellen Verlauf und Status der Netzhautdegeneration, zum anderen von der Schnittstelle zwischen Implantat und Netzhaut und der Qualität der mit elektrischer Stimulation erzielbaren neuronalen Aktivierung. Biophysikalische Ansatzpunkte zur funktionellen Weiterentwicklung der Implantate, die sich an der Physiologie der Netzhaut (Zelldichte, intraretinale Verschaltungen) orientieren, bieten die technische Seite der Schnittstelle (Elektrodenmaterialien, -größe und -dichte) sowie die Stimulationsprotokolle (Zeitverläufe der elektrischen Reize, räumlich-zeitliche Stimulationsmuster), mit denen visuelle Informationen in die degenerierte Netzhaut eingespeist werden. Die Optimierung der Reizparameter kann durch eine detaillierte Analyse kortikaler Antworten mit geeigneten elektrophysiologischen und optischen Methoden unterstützt werden. Dieser Artikel beschreibt die physiologischen und biophysikalischen Grundlagen der elektrischen Netzhautstimulation und die daraus resultierende retinale und kortikale Aktivierung.

Abstract

In Germany, about 30,000 to 40,000 people suffer from retinitis pigmentosa (RP), which ultimately results in blindness. The only aid to blind RP patients are retinal implants: These have been under development for several years and have now been approved as a medical product. Retinal implants produce visual perceptions in response to electrical stimulation of the degenerated retina and are useful in the everyday life of blind people. However, the currently achievable quality of vision is such that people with a retinal implant are still legally blind. The visual quality that can be achieved with epi- and subretinal implants depends not only on patient-specific factors such as individual history and status of retinal degeneration, but especially on the interface between implant and retina and the quality of the achievable neuronal activation. Biophysical approaches to functional improvements of the implants are founded on the physiology of the retina (cell density, intraretinal interconnections), are based on technical optimisation of the interface (electrode materials, size and density), and exploit the stimulation protocols with which visual information is fed into the degenerated retina (time courses of electrical stimuli, spatiotemporal stimulation pattern). Optimisation of stimulation parameters can be supported by a detailed analysis of cortical responses, with appropriate electrophysiological and optical methods. This article looks at both the physiological and biophysical fundamentals of electrical retinal stimulation, as well as the resulting retinal and cortical activation.

Schlüsselwörter

Retinitis pigmentosa - Retinaimplantat - elektrische Stimulation - kortikale Aktivierung - Sehqualität

Key words

retinitis pigmentosa - retina implant - electrical stimulation - cortical activation - quality of vision

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