1. A visual neuroprosthetic device comprising an array of nanoscale waveguides disposed on a substrate, each nanoscale waveguide in the array having a photovoltaic material located between an internal conductor and an external conductor, wherein each nanoscale waveguide receives, propagates, and converts incident light into electrical neural signals, and wherein a site density of the nanoscale waveguides on the substrate is the same as or greater than the site density of photoreceptors in the human retina.