Are Subretinal Microphotodiodes Suitable as a Replacement For Degenerated Photoreceptors

The feasibility of a retinal prosthesis for the blind has been discussed since the 1950s. Early attempts to realize a subretinal implantable prosthesis suffered from technical and microsurgical limitations at that time. Nowadays these problems can be solved because of the amazing progress that has been made in the fields of intraocular surgery, silicon microfabrication and our knowledge of the silicon/neuron junction. Therefore, a new attempt to develop a retinal prosthesis seems justified. While other research groups1, 2, 3 have concentrated their efforts on the development of an epiretinal visual prosthesis, which receives energy and preprocessed visual information via a relatively complex telemetric system, Chow and coworkers4, 5, 6, 7 published the concept of a retinal implant consisting of thousands of microphotodiodes. The principle of this concept is based on an implant that is placed in subretinal space and stimulates the underlying retinal cells with the photocurrents generated solely from the incident light (Fig. 1).