Ph.D Thesis

Ph.D StudentReutsky-Gefen Inna
SubjectOptogenetic Patterned Control of Channelrhodopsin-2
Expressing Retinal Ganglion Cells
DepartmentDepartment of Biomedical Engineering
Supervisor PROF. Shy Shoham


Outer retinal degenerative diseases such as Age-related Macular Degeneration are among the leading causes of blindness in the Western world. The progression of these diseases is accompanied by a gradual loss of photoreceptors, leaving the non-light absorbing retinal cell layers, primarily the retinal ganglion cells, relatively preserved. Retinal prostheses for patients with outer-retinal degenerative diseases could interface directly with the surviving retinal neurons using electrode array implants. However, electrical stimulation requires a surgical procedure, and suffers from limited spatial specificity which is a key requirement for functional vision restoration. Recently, light-sensitive proteins that photosensitize quiescent neurons have generated unprecedented opportunities for optogenetic neuronal control, inspiring early development of optical retinal prostheses. Optogenetic stimulation may be used as an alternative to electrical stimulation for spatio-temporally precise, minimally-intrusive control of neurons.

Our work focused on development and characterization of techniques for optogenetic control of neural activity in blind retinas, and their further implementation into a feasible neuroprosthetic device. We studied and characterized two digital projection techniques; digital mirror devices and digital holographic projection systems, which were used to optically drive neural activity of Channelrhodopsin-2 expressing retinal ganglion cells in vitro in relevant animal models of blindness.

We show that both systems are able to drive optogenetic patterned activity in ChR2-expressing retinas. The electrophysiological results demonstrate efficient parallel control of neural population activity with single cell resolution and high temporal precision, whose quantitative characteristics are strongly dependent on the amount of light delivered to the retinal ganglion cell's membrane. Moreover, we demonstrate the emulation of natural activity of retinal ganglion cells in a blind ChR2-expressing retina using the holographic projection system. Finally, to further assess the application of using optogenetic probes to the human visual system we evaluate the efficacy of different adeno-associated viral vectors for transfecting neural tissues with Channelrhodopsin-2.

The high-precision optogenetic control characteristics demonstrated in this work using the new optical systems developed, outperform previously achieved results using multi-electrode stimulation in vitro, and may significantly advance the development of a non-contact optical retinal neuroprosthetic device towards the restoration of functional vision in people with outer retinal degeneration. However their performance should first be evaluated in vivo in order to compare their characteristics relative to currently approved electrical retinal prosthesis which was already shown to be functional and beneficial in humans for over a decade.