Article | REF: E5180 V1

Visual function and the visual pathway Implants from the eye to the brain

Authors: Diep NGUYEN, Jocelyn BOUTZEN, Serge PICAUD

Publication date: October 10, 2020, Review date: April 12, 2021

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ABSTRACT

Vision disorder and eye disease hinder the processing of visual information, either at the photoreceptors in the retina or somewhere in the upper visual domain, but can leave the downstream neurons intact. Classified as brain-machine interfaces, visual prostheses aim at restoring vision since the 1970s. They electrically stimulate the remaining healthy neurons to provide visual information to the patient and consequently, to improve their quality of life. This article presents the principles of electrically stimulating the visual pathway. It describes the latest advances in implant technology and give an overview on future developments.

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AUTHORS

  • Diep NGUYEN: Doctoral student, Sorbonne University, INSERM, CNRS, Institut de la Vision, Paris, France

  • Jocelyn BOUTZEN: Post-doctoral fellow, CEA, LIST, Laboratoire Capteurs Diamant, 91191, Gif-sur-Yvette, France

  • Serge PICAUD: Research Director, Sorbonne University, INSERM, CNRS, Institut de la Vision, Paris, France

 INTRODUCTION

According to the World Health Organization, eye diseases affect nearly 2.2 billion people worldwide. They have a major impact on quality of life. Although the majority of vision disorders can be treated by medical consultation or surgery, 20% are linked to hereditary and/or incurable pathologies, such as retinal diseases or glaucoma. Retinal diseases, such as retinopathy pigmentosa (RP) and age-related macular degeneration (AMD), affect the photoreceptors in the retina, while glaucoma and diabetic retinopathy affect the ganglion cells, and therefore by extension the optic nerve connected to the brain. While degeneration of the photoreceptors leaves the other layers of the retina relatively intact, which can then be electrically stimulated to restore sight, atrophy of the optic nerve removes any eye-brain connection. Visual restoration must therefore take place in the higher visual areas of the brain.

Despite the development of alternative strategies (transplantation, optogenetic therapy), electrical stimulation remains the only clinically validated approach to restoring vision in people suffering from severe blindness as a result of RP. Over 40 years of research have been devoted to understanding the role of electrical stimulation, and to improving its effectiveness in visual prostheses.

Phosphenes are visual sensations that occur following electrical stimulation. They were first mentioned in connection with a visual prosthesis when Brindley and Lewin placed electrodes on the visual cortex of a blind subject. Over the years, human trials have tested the effects of electrical stimulation in all areas of the optic pathway, demonstrating its restorative properties on vision.

This article seeks to present the different strategies that have been explored to restore visual function in blind patients using electrical stimulation. It includes a presentation of the anatomy of the eye, visual diseases and the electrophysiological interaction between neuronal tissue and the electrode. Since the 2000s, these strategies have evolved in terms of the type of stimulation delivered, its location and the structure of the implants. This article presents the implants currently on the market, as well as those currently in clinical trials. We also look at some of the innovations that have contributed to their development, as well as future challenges in this field of brain-machine interface applications.

A glossary of terms is provided at the end of the article.

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KEYWORDS

implant   |   retinal degeneration   |   artificial vision   |   electrical stimulation


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Visual function and the optical pathway