Pixium Vision's Bionic VRS are systems intended to partially replace the normal physiological functions of the eye's photoreceptor cells by electrically stimulating the nerve cells of the inner retina, which then transmit the visual information to the brain via the optic nerve.

Due to its construction, the retina can be artificially stimulated in two ways:

Epi-retinal stimulation: The electrode array is placed on the surface of the retina. This approach
   involves sending a high-content signal directly to the ganglion cells.

Pixium’s Bionic IRIS® VRS is based on an epi-retinal implant:

Sub-retinal stimulation is achieved by partially replacing the photoreceptor layer by an electrode
   array that stimulates bipolar cells and the inner retina. The approach enables a more physiological
   processing of the visual signal.

Pixium’s Bionic PRIMA VRS is based on a sub-retinal implant: