The combination of photodiodes and electrodes therefore provides point-to-point stimulus of retinal bipolar cells, eliminating the need for an external camera and permitting object tracking INK-128 via saccadic eye movements. The device was trialed on 9 patients with retinitis pigmentosa (n=8) and cone-rod

dystrophy (n=1), resulting in light perception by 8 patients with one excluded due to complications during the implantation procedure ( Stingl et al., 2013). Functionally, the results were variable, with 7/8 patients able to localize a light source, 5/8 able to detect motion and grating acuity testing able to be performed in 6/8 recipients. The device was recently approved for marketing in the European Union (Retina Implant AG, 2014). Whilst Alpha IMS is wirelessly powered via a subdermal coil behind the ear that is tethered to the implant (Stingl et al., 2013), Chow et al. (2004) recently described an alternative photodiode-based array with 5000 stimulating elements that is powered by incident light.

This device, referred to by its developers as the “Artificial Silicon Retina” (ASR), has undergone limited clinical trials (Chow et al., 2010). Bionic Vision Australia is also developing a suprachoroidal retinal implant. In the popular press, the group recently reported on the first human implantation of a 24-electrode prototype device (Bionic Vision Australia, 2012), with development and testing of improved devices ongoing (Villalobos et al., 2013). Veraart et al. (1998) Nutlin-3a datasheet were the first to attempt electrical stimulation of the optic nerve as a basis upon which to develop a visual prosthesis. The method can be applied in blind patients with

surviving retinal ganglion cells and/or cAMP an intact optic nerve, and was initially trialed on a 59-year old female with retinitis pigmentosa (Veraart et al., 1998). After demonstrating that phosphenes could be reproducibly elicited at safe stimulation currents, the group developed a computational model that could predict the location and size of percepts as a function of stimulus parameters (Delbeke et al., 2003). With sufficient training, recipients could recognize and orient complex shapes (Brelen et al., 2005 and Veraart et al., 2003) and perform object localization, discrimination and grasping (Duret et al., 2006). Phosphenes could be elicited in all four visual field quadrants, although they were irregularly distributed and subtended a relatively narrow portion of the horizontal field (Delbeke et al., 2003). The surgical technique was relatively simple, with the first patient receiving an implant consisting of a four-electrode, non-penetrating silicon cuff implanted around the optic nerve, accessed via a pterional craniotomy and a trans-Sylvian approach (Veraart et al., 1998).