Polymer pRobes fOr a VISual prOsthesis

Introduction

Approximately forty million people across the world are blind, a condition with serious consequences for a person’s autonomy. Restoration of visual function in blind individuals is an important scientific goal with large societal benefits. In a large fraction of blind patients, the connection between the eye and the brain has degenerated so that restoration of a rudimentary form of vision can only be achieved in pathways downstream from the retina, like the visual cortex. PROVISO tests the feasibility of a new approach for a cortical visual prosthesis by implanting flexible polymer electrodes into the visual cortex that can be stimulated electrically to create a rudimentary form of vision.

Phosphenes and Visual Perception

Weak electrical currents applied to an electrode in the visual cortex induce an artificial percept of light, called “phosphene.” Multiple phosphenes can be used to build up a shape, just as the lights of a matrix board along the highway generate letters. A promising approach to restore vision involves inserting tiny electrodes into the visual cortex, close to the neurons, so that weak currents result in phosphene perception.

Challenges to Overcome

There are two problems that need to be solved before the prosthesis can become a treatment for blind individuals:

1. The first problem is that the electrodes available for chronic implantation are made of silicon or metal, which causes a tissue response (gliosis) that degrades the interface with the tissue after several months.
2. The second problem is coverage of the visual field. In humans, much of the primary visual cortex (V1) is not located on the surface of the brain, but inside a sulcus, making it difficult to access.

Proposed Solutions

PROVISO will develop methods to implant flexible electrodes that cause little tissue damage and remain functional across longer time scales into the brain. These electrodes will be implanted deep into several brain areas, thereby providing good coverage of the visual field.