A method to assess the location and positional stability of supra-choroidal retinal neuroprostheses

Electrical stimulation of the retina is now firmly established as a means of restoration of rudimentary vision for blindness particularly that caused by retinitis pigmentosa. Of the various approaches, the novel positioning of an ultra-thin stimulating electrode array (SEA) posterior to the choroid has shown promising results. Following their implantation, reliable imaging methods are essential to establish the SEA's location relative to the optic disk and retinal vasculature. Because the opacity of the choroid precludes the use of conventional light-based fundus imaging, we developed an instrument (Wangiscope) that relies on infra-red illumination from LEDs. This instrument generates video from an inexpensive web camera whose optics have been enhanced for wide-angled retinal imaging by adding two plano-concave lenses to the existing lens system. When imaging, the instrument's outer lens, protected by a thin plastic film and methylcellulose gel, contacts the cornea while a probe comprising two 940 nm wavelength LEDS is held against the sclera. This instrument has provided useful retinal images in acute experiments using the Felus catus and also proof of the positional stability over 3 months of SEAs in the Ovis aries.