Retinal prostheses: optimizing electrical stimulation for suprachoroidal retinal prostheses

Submission note: A thesis submitted in total fulfilment of the requirements for the degree of Doctor of Philosophy to the School of Engineering and Mathematical Sciences, Faculty of Science, Technology and Engineering, La Trobe University, Bundoora.

Retinal prostheses are a promising treatment for people suffering from severe retinal degenerations. These prostheses work by electrically stimulating residual retinal cells in order to generate a visual percept. Currently there are few guidelines and recommendations that can aid in selecting efficacious stimulus parameters. In addition, the mechanisms through which these prostheses work are unclear and fundamental knowledge of the interactions between electrical stimulation and the retinal cells is lacking. Understanding these mechanisms and the interaction for electrical stimulation with retinal cells and higher centres will improve clinical patient outcomes. Efficacy in general refers to the ability to stimulate neural population with lowest charge, controlled spatial activation profiles and minimal power. Optimizing stimulation parameters may allow the clinical outcome to be less sensitive to the position of the electrode, reduce threshold for neural stimulation, improve spatial selectivity and use less power. In this thesis we look at addressing large count electrode arrays and impedance monitoring. Impedance monitoring and fault detection is necessary as it has implications for ensuring safe and effective stimulation as well as the power required to stimulate neural tissue. Electrical targeting can be achieved by choosing optimal pulse shape, polarity, duration, inter-phase gap and frequency. Understanding the fundamentals will aid in the rational selection of stimulation parameters and development of retinal prostheses.