Patterned optical activation of retinal ganglion cells

Neuroprosthetic retinal interfaces depend upon the ability to bypass the damaged photoreceptor layer and directly activate populations of retinal ganglion cells (RGCs). To date, the preferred approach to this task largely relies on electrode array implants. We are currently pursuing two alternative methods for light-based direct activation of the RGCs. The first method is based on applying caged glutamate over the retina and uncaging it locally to obtain RGC excitation. The second method is to artificially cause RGCs to express Channelrhodopsin II (ChR2), a light-gated cation channel. In addition to being non-contact, optical techniques lend themselves relatively easily to a variety of technologies for achieving patterned stimulation with high temporal and spatial resolution. Using the Texas Instruments Digital Light Processing (DLP - DMD) technology, we have developed an optical stimulation system capable of controlled, large-scale, flexible stimulation of the retinal tissue with high temporal accuracy. In preliminary studies, we are performing patterned photo-stimulation experiments using samples of caged fluorescent probes and in rat retinas that were virally transfected with ChR2.