The best way to rehabilitate blindness is to directly act upon a peripheral and passive neural structure instead of direct stimulation of the visual cortex or of the retina. This is only possible when the optic nerve fibres are electrically activated in a safe and selective manner. Researchers have developed a prototype of a Microsystems based Visual Prosthesis (MIVIP) interfaced with the optic nerve. This three years Esprit supported project might be able to help about 140.000 blind people in the industrialised countries.
The MIVIP researchers hope to have realised by the end of 1999 a standard prosthesis prototype which has to be implanted to a blind volunteer in order to assess the performances. The first objective is to design an artificial eye connected, via an external visual processor and an implantable neuro-stimulator, to the optic nerve. The interface of the visual prosthesis with the nervous system is a cuff electrode wrapped around the optic nerve. The final feature constitutes a transcutaneous power and data RF link. This, in fact, is a basic component for many active implanted devices.
The greatest challenge forms the optic nerve stimulation. Before the start of the project, some partners already had developed a commercialised spiral cuff electrode and demonstrated selective fibres activation. To enhance the effectiveness and feasibility of this stimulation, the researchers apply computer simulation by finite elements methods. In trying to assess the optic nerve functionality of blind volunteers, the MIVIP people have discovered phosphene perception in response to electrical activation using surface electrodes. A phosphene consists in a visual perception evoked by a non luminous stimulation.
The artificial retina designed by MIVIP will include gradual resolution from the fovea to the periphery as well as photodetector local gain adaptation. To allow motion detection in the periphery, the spatial and temporal variation in the image will be enhanced. This component will also be used for a non-invasive sensory substitution visual prosthesis. In the near future, about 140.000 blind people might benefit from MIVIP among which about one half suffer from Retinitis Pigmentosa.
The project is built upon a synergy between Belgian University Laboratories and both European and American industrial companies. The general aim is to gather all the required knowhow for the sophisticated production of active implanted devices and to incorporate quality control as well, along with the respect of complex medical regulations. The MIVIP site has more detailed information in store for you.