Fiber-optic sensor system for evaluating spatial selectivity of stimulation by a micro-electrode array

A fiber optic sensor has been developed for use in vertically positioning micro-electrode arrays in close proximity to the retina of a live subject. Closely spaced optical fibers illuminate and collect reflections from the retinal surface, and the resultant output electronically processed and used to drive an automated positioning circuit. Systematic evaluation of fiber types and separation on both specular and diffuse reflectors is reported, resulting in the choice of multi-mode fibers on 125 μm centers for retinal experimentation. In vitro and in vivo evaluations produced quite similar sensor responses, slowly rising to a peak at a height of 300 μm and sharply dropping to zero as the surface is approached. The sensor has applications in assessing the spatial selectivity of stimulation of a multi-electrode array versus height, and can be potentially adapted for lateral positioning