Electrical devices for visual restoration.

Given the rising number of patients with blindness from macular, optic nerve, and visual pathway disease, there is considerable interest in the potential of electrical stimulation devices to restore vision. Electrical devices for restoration of visual function can be grouped into three categories: (1) visual prostheses whose goal is to bypass damaged areas and directly activate downstream intact portions of the visual pathway; (2) electric field stimulation whose goal is to activate endogenous transcriptional and molecular signaling pathways to promote neuroprotection and neuro-regeneration; and (3) neuromodulation whose stimulation would resuscitate neural circuits vital to coordinating responses to visual input.  In this review, we discuss these three approaches, describe advances made in the different fields, and comment on limitations and potential future directions.