gms | German Medical Science

Objective: To describe stimulation paradigms to achieve low-threshold activation to effect selective stimulation of retinal ganglion cells via an electrode array implanted within the supra-choroidal space.

Materials and Methods: A stimulation paradigm that we have described as ‘quasi-monopolar’ (QMP) divides the return-path of stimulation across a ring of guard electrodes adjacent to and surrounding the stimulating electrode, and a distant monopolar return. Through acute in vivo testing in the feline, we have determined that the effect of the of guard ring electrodes is that activation is largely contained to within the ring. However, activation thresholds using this approach alone are approximately three times higher with respect to monopolar stimulation alone owing to inefficient, lateral shunting of the electric fields. By splitting a proportion of the return current to a distant monopole, the electric field is directed towards the target neurons. The monopolar component of the return current effectively reduces the threshold of activation while the guard ring component maintains the localisation of activation. QMP further affords the possibility of delivering stimulation from multiple sites simultaneously with a significant reduction in cross-talk between stimulating sites relative to monopolar stimulation alone.

Discussion: The QMP stimulation paradigm provides the dual benefits of focused activation via guard-ring localisation with reduced stimulation thresholds of monopolar stimulation.

Acknowledgement: This research was supported by the Australian Research Council (ARC) through its Special Research Initiative (SRI) in Bionic Vision Science and Technology grant to Bionic Vision Australia (BVA).