3 The procedure
3.1 Retinitis pigmentosa causes loss of retinal photoreceptors but inner retinal cells (ganglion and bipolar cells) remain intact. Subretinal prosthesis systems aim to restore perception of light, movement, and shapes by surgically implanting a microchip behind the retina. The microchip mimics the function of damaged outer retinal photoreceptors by absorbing light and converting it into retinotopically correct electrical pulses that stimulate the overlying bipolar cell layer. The bipolar cells propagate the signal to downstream retinal cells, which send visual information to the brain.
3.2 Implantation of the microchip is done with the patient under general anaesthesia. A vitrectomy is performed and the microchip is implanted underneath the macula using a transscleral, then subretinal approach. The microchip connects to a thin cable that exits the eye at the equator, through the choroid and sclera, and runs under the skin to a power source which is fixed to bone in the retroauricular region. This, in turn, connects to an external power source/control unit via a removable, surface mounted induction loop.