Page 363 - Handbook of Biomechatronics

Current Advances in the Design of Retinal and Cortical Visual Prostheses 357

Fig. 1 Schematic representation of the visual pathway from the eyes to the brain, and
visual prostheses implantation sites. Flat arrays are placed next to the retina, around the
optic nerve or next to the visual cortex, and a penetrating shaft-like array to target the
lateral geniculate nucleus (LGN). For cortical and optic nerve prostheses, the electrodes
in the array can be either flat or needle-like penetrating electrodes.

degeneration (AMD). While these conditions severely damage the photo-
receptors, the remaining neurons in the retina, in particular bipolar cells
and the output retinal ganglion cells (RGCs), may still be activated by arti-
ficial stimuli, leading to elicitation of visual sensations (Santos et al., 1997;
Stone et al., 1992). Cortical prostheses can be applied in cases when the
RGCs degenerate or after ON injury, for example, in cases of glaucoma,
optic neuropathy, severe retinal disease, diabetic retinopathy, optic neuritis,
large pituitary/parasellar tumors, bilateral enucleation, and bilateral retino-
blastoma, as well as ON and eye trauma.
The concept of artificial vision was demonstrated by several pioneering
studies dating back to the 18th century. In 1755, Charles LeRoy reported
that electrical discharge applied to the surface of the eye of a patient blinded
from cataract during a surgery, resulted in the sensations of light spots (phos-
phenes) (LeRoy, 1755). Later, Brindley (1964) showed that visual sensations
can be evoked by stimulation of the retina. Probing direct stimulation of the