Optogenetic approaches to retinal prosthesis.

The concept of visual restoration via retinal prosthesis arguably started in 1992 with the discovery that some of the retinal cells were still intact in those with the retinitis pigmentosa disease. Two decades later, the first commercially available devices have the capability to allow users to identify basic shapes. Such devices are still very far from returning vision beyond the legal blindness. Thus, there is considerable continued development of electrode materials, and structures and electronic control mechanisms to increase both resolution and contrast. In parallel, the field of optogenetics--the genetic photosensitization of neural tissue holds particular promise for new approaches. Given that the eye is transparent, photosensitizing remaining neural layers of the eye and illuminating from the outside could prove to be less invasive, cheaper, and more effective than present approaches. As we move toward human trials in the coming years, this review explores the core technological and biological challenges related to the gene therapy and the high radiance optical stimulation requirement.