Suprachoroidal electrical stimulation: effects of stimulus pulse parameters on visual cortical responses.
OBJECTIVE
Neural responses to biphasic constant current pulses depend on stimulus pulse parameters such as polarity, duration, amplitude and interphase gap. The objective of this study was to systematically evaluate and optimize stimulus pulse parameters for a suprachoroidal retinal prosthesis.


METHODS
Normally sighted cats were acutely implanted with platinum electrode arrays in the suprachoroidal space. Monopolar stimulation comprised of monophasic and biphasic constant current pulses with varying polarity, pulse duration and interphase gap. Multiunit responses to electrical stimulation were recorded in the visual cortex.


RESULTS
Anodal stimulation elicited cortical responses with shorter latencies and required lower charge per phase than cathodal stimulation. Clinically relevant retinal stimulation required relatively larger charge per phase compared with other neural prostheses. Increasing the interphase gap of biphasic pulses reduced the threshold of activation; however, the benefits of using an interphase gap need to be considered in light of the pulse duration and polarity used and other stimulation constraints. Based on our results, anodal first biphasic pulses between 300-1200 µs are recommended for suprachoroidal retinal stimulation.


CONCLUSIONS
These results provide insights into the efficacy of different pulse parameters for suprachoroidal retinal stimulation and have implications for the design of safe and clinically relevant stimulators for retinal prostheses.
Bionics Institute, VIC-3002, Australia. Department of Electronic Engineering, La Trobe University, VIC-3086, Australia.
Sam E
SE
John
Mohit N
MN
Shivdasani
Chris E
CE
Williams
John W
JW
Morley
Robert K
RK
Shepherd
Graeme D
GD
Rathbone
James B
JB
Fallon
D000704:Analysis of Variance; D000818:Animals; D002415:Cats; D002829:Choroid / Q000502:physiology*; D004558:Electric Stimulation; D004567:Electrodes, Implanted; D005071:Evoked Potentials / Q000502:physiology; D005074:Evoked Potentials, Visual; D012160:Retina / Q000502:physiology; D014793:Visual Cortex / Q000502:physiology*; D057488:Visual Prosthesis