Sensory Systems/Neurosensory Implants/Visual Implants

Other Visual Implants

In addition to the stimulation of the retina, also other elements of the visual system can be stimulated

Stimulation of the Optic Nerve

With cuff-electrodes, typically with only a few segments.

Advantages:

• Little trauma to the eye.

Challenges:

• Not very specific.

Cortical Implants

The Visual Cortical Implant

Dr. Mohamad Sawan, Professor and Researcher at Polystim neurotechnologies Laboratory at the Ecole Polytechnique de Montreal, has been working on a visual prosthesis to be implanted into the human cortex. The basic principle of Dr. Sawan’s technology consists in stimulating the visual cortex by implanting a silicium microchip on a network of electrodes made of biocompatible materials and in which each electrode injects a stimulating electrical current in order to provoke a series of luminous points to appear (an array of pixels) in the field of vision of the sightless person. This system is composed of two distinct parts: the implant and an external controller. The implant lodged in the visual cortex wirelessly receives dedicated data and energy from the external controller. This implantable part contains all the circuits necessary to generate the electrical stimuli and to oversee the changing microelectrode/biological tissue interface. On the other hand, the battery-operated outer control comprises a micro-camera which captures the image as well as a processor and a command generator which process the imaging data to select and translate the captured images and to generate and manage the electrical stimulation process and oversee the implant. The external controller and the implant exchange data in both directions by a powerful transcutaneous radio frequency (RF) link. The implant is powered the same way. (Wikipedia [1])

Advantages:

• Much larger area for stimulation: 2° radius of the central retinal visual field correspond to 1 mm² on the retina, but to 2100 mm² in the visual cortex.

Challenges:

• Implantation is more invasive.
• Parts of the visual field lie in a sulcus and are very hard to reach.
• Stimulation can trigger seizures.