Background
Some progressive dieases specifically affect the retina. Two of the most common are retinitis pigmentosa and macular degeneration. In both cases, the photoreceptor cell die leaving the affect person with profound vision loss. These diseases have led to research into the development of an artifical retina. Below, you can see how some of these artifical retinas may eventually function.
Department of Energy Model
The United States Department of Energy has sponsored research into one model of an artificial retina. In this model, a camera is placed in a pair of eyeglasses. The camera receives visual information and transmits the infromation to a microprocessor in the earpiece of the glasses. The microprocessor converts the signal from the camera to a digital signal is transmitted to a device implanted on the retina. This retinal implant sends electrical signal directly to the ganglion cells of the retina.This information is then sent back through the optic nerve to the brain.
This device has been been tested in six patients. Presently, this retinal implant has sixteen electrodes meaning that individuals with the implant have 16 discreet regions that can receive light. These individuals are all now able to discern light from dark environments and sense the presence of large objects.
http://artificialretina.energy.gov/howartificialretinaworks.shtml
Optobionics Model
A second investigational artificial retina has been developed by the company Optobionics. The artificial retina developed by Optobionics consists of a microchip that has a number of photoelectrodes placed on it. The micrcoship is then implanted in the space behind the retina. See image below.
The Optobionic chip has 5000 photoelectrodes placed on it giving it potentially more acuity than the department of defense retina. It is also powered by incident light striking the chip. This is different than the Deparment of Energy retina which is powered by a battery worn by the patient. The Optobionics electrode is connected with the ganglion cells that make up the optic nerve. Initial results from the Optobionics retina have shown promise. Patients with the implant have not shown any signs of rejection, have shown signs of cortical activation, and report sensations of light.
From Chow, et al. (2004) Archivies of Ophthalmology Vol 122 p 460.