A Look at Various Approaches to Prosthetic Vision
Artificial vision for the blind lies ahead, and this research and development proceeds in competition with regeneration medicine approaches that aim to reverse degeneration and damage in the eye. Some of the most advanced prototype devices presently in use take the approach of linking a camera to an electrode grid embedded in the retina, building a moving picture of glowing dots. But this isn't the only way forward:
Blindness is still one of the most debilitating sensory impairments, affecting close to 40 million people worldwide. Many of these patients can be efficiently treated with surgery or medication, but some pathologies cannot be corrected with existing treatments. In particular, when light-receiving photoreceptor cells degenerate, as is the case in retinitis pigmentosa, or when the optic nerve is damaged as a result of glaucoma or head trauma, no surgery or medicine can restore the lost vision. In such cases, a visual prosthesis may be the only option. Similar to cochlear implants, which stimulate auditory nerve fibers downstream of damaged sensory hair cells to restore hearing, visual prostheses aim to provide patients with visual information by stimulating neurons in the retina, in the optic nerve, or in the brain's visual areas.In a healthy retina, photoreceptor cells - the rods and cones - convert light into electrical and chemical signals that propagate through the network of retinal neurons down to the ganglion cells, whose axons form the optic nerve and transmit the visual signal to the brain. Prosthetic devices work at different levels downstream from the initial reception and biochemical conversion of incoming light photons by the pigments of photoreceptor rods and cones at the back of the retina. Implants can stimulate the bipolar cells directly downstream of the photoreceptors, for example, or the ganglion cells that form the optic nerve. Alternatively, for pathologies such as glaucoma or head trauma that compromise the optic nerve's ability to link the retina to the visual centers of the brain, prostheses have been designed to stimulate the visual system at the level of the brain itself.
While brain prostheses have yet to be tested in people, clinical results with retinal prostheses are demonstrating that the implants can enable blind patients to locate and recognize objects, orient themselves in an unfamiliar environment, and even perform some reading tasks.
Link: http://www.the-scientist.com/?articles.view/articleNo/41052/title/The-Bionic-Eye/