Cochlea implants function by electrical stimulation of spiral ganglion cells in the ear even though severe hair cell damage exists. This is shown especially in donor eyes as well as in experiments of some animal models. The project group at the Johns Hopkins University in Baltimore has shown in several short tests with blind RP- patients that by hand held electrodes visual sensation in some parts of the visual field can be triggered. A lot of different aspects need to be investigated and tested carefully before implantation of the prosthesis into the human eye. Problems of immune reaction, biocompatability and longterm stability have to be solved.
Researchers have to test alternative materials for building and coating the implant.
On the one hand the implant has to be resistant to corrosive salt water in the body and on the other hand the implant must not exert pressure or poison the delicate retina. It has to be extremely flexible in order to match the natural curve of the retina and the best method of positioning the implant must be chosen, so that the movements of the eye do not harm the retina. The energy problem still has to be solved in the all the currently known projects. While three of the four projects known to the writer require external energy, the lowest charge density has to be tested out, so that damage can be avoided. The fourth project claims to get along with daylight energy only and tries to optimise the light induced stimulation.