Brightness as a Function of Current Amplitude in Human Retinal Electrical Stimulation

With the goal of eventually restoring functional vision in patients with retinal degenerative diseases, USC/Second Sight Medical Products, Inc. chronically implanted blind human subjects with a prototype epiretinal prosthesis consisting of a 4 x 4 array of 16 stimulating electrodes. To accurately represent a visual scene, a visual prosthesis must convey luminance information across a range of brightness levels. To achieve this, the brightness of phosphenes produced by an individual electrode should scale appropriately with luminance, and the same luminance should produce equivalently bright phosphenes across the entire electrode array. The goal was to examine how apparent brightness changes as a function of stimulation intensity across electrodes.