The idea behind vision restoration with visual prostheses is to produce phosphenes, the sensation of seeing spots of light arranged in patterns. So far, retinal prostheses (devices that directly stimulate retinal cells within the eyeball) have demonstrated to improve the quality of life in blind people affected by retinal diseases, such as Retinitis pigmentosa and age-related macular degeneration, by allowing them to see objects and letters.
Retinitis pigmentosa is a hereditary disease affecting a few million people worldwide, and today, about half a million might need a retinal implant. However, only a fraction of the patients qualifies for retinal implants for clinical reasons. The remaining people, for example those with severe trauma and retinal detachment are not eligible as those conditions are contraindications for retinal implants. Instead, an optic nerve implant, placed in contact with the optic nerve, will be effective to help these patients.
Previous attempts to stimulate the optic nerve were performed in the 1990s with particular electrodes wrapped around the nerve (called cuff). However, these electrodes are rigid, and they might move, causing the electrical stimulation of the nerve fibers to become unstable. Moreover, they have limited selectivity because they recruit mostly external fibers.
We believe that intraneural electrodes are a valuable solution for sensory and motor function restoration. Their high translational potential makes this type of electrodes very promising. In fact, previous reports involving intraneural electrodes showed the successful selective activation of muscular activity and the selective restoration of touch sensation.
In our laboratories, We decided to test an intraneural electrode array for optic nerve stimulation, and we named it OpticSELINE. We started our project by tailoring the OpticSELINE to the anatomy of the nerve and the surgical constraints. Excited by the idea of restoring visual perceptions with selective optic nerve stimulation, we decided to test the OpticSELINE in-vivo. Working on anaesthetized rabbits and by paring our experimental data with numerical modelling and analysis, we showed that the electrical stimulation of the optic nerve via the OpticSELINE induces selective activation patterns in the visual cortex.
This novel intraneural electrode array will prove an invaluable tool in basic research, enabling further investigations of the effects of electrical stimulation on the visual system. On the other hand, this device will be further developed into a visual prosthesis to aid blind patients.
Written by Diego Ghezzi and Silvestro Micera