Sensory Aids

Nano and related micro technologies are being used to develop a new generation of smaller and potentially more powerful devices to restore lost vision and hearing functions. The devices collect and transform data into precise electrical signals that are delivered directly to the human nervous system.

Degenerative diseases of the retina, such as retinitis pigmentosa or age related macular degeneration, decrease night vision and can progress to diminishing peripheral vision and blindness. These retinal diseases may lead to blindness due to a progressive loss of photoreceptors (rods and cones), the light sensitive cells of the eye.

In cases where the neural wiring from the eye to the brain is still intact but the eyes’ lack photoreceptor activity, photoreceptor loss could be compensated by bridging or bypassing the destroyed photoreceptors and artificially stimulating the adjacent intact cells. Artificially generated impulses could reach the brain and produce visual perception, thereby restoring some elementary vision.

In severe hearing loss, patients typically have absent or malfunctioning sensory cells in the cochlea. In a normal ear, sound energy is converted to mechanical energy by the middle ear, which is then converted to mechanical fluid motion in the cochlea. Within the cochlea, the inner and outer hair sensory cells are sensitive transducers that convert mechanical fluid motion into electrical impulses in the auditory nerve.

Cochlear implants are designed to substitute for the function of the middle ear, cochlear mechanical motion, and sensory cells. The implants transform sound energy into electrical energy that will initiate impulses in the auditory nerve. Cochlear implants include an electronic circuit that is surgically placed in the skull behind the ear on the mastoid process of the temporal bone. This circuit is attached to a bundle of tiny wires that are inserted into the cochlea. At the end of the wires are typically 8 to 24 electrodes that cause a different pitch percept when stimulated. The other part of the device is external and has a microphone, a speech processor, and connecting cables.

Current cochlear implants have a number of drawbacks. They require major surgery and can eliminate any remaining natural hearing. Because of their large size, current cochlear implants often stimulate several nerve fibers at once. This causes users to experience imprecise or distorted sound, especially with complex sounds like music.