A Surgical Techniquel For Chronic Active Stimulation With A Suprachoroidal Electrode Array in a Feline Model

Abstract

Purpose: : To develop a surgical approach for implanting a suprachoroidal electrode array for chronically stimulating the retina in a feline model.

Methods: : Seven normally sighted adult cats were implanted with a conformable suprachoroidal electrode array via an approach developed from initial acute surgeries and then passive chronic surgery. The devices consist of a suprachoroidal electrode array, with a percutaneous lead, two dural recording electrodes, a return electrode and fixation arm. The approach involves the suprachoroidal implantation of the array, extraorbital tunnelling of the lead and recording electrodes and fixation arm,anterior to the pinna and over the vertex , where they were stabilised with titanium clips. The recording electrodes are placed over the contralateral visual cortex on the dura. The fixation arm is implanted in the mastoid bulla and the percutaneous lead is passed subcutaneously to a point between the shoulder blades. Following recovery the cats were fitted with wearable multichannel stimulators for 3 months. Function was assessed over a three month period by measuring both behavioural and cortical responses. Safety was assessed by determining ocular health through regular fundus photography, OCT and ERG during the study as well as histopathological assessments using the contralateral eye as a control.

Results: : The implant surgeries took 4-5 hours with minimal complications. The electrodes and lead assemblies remained viable throughout the 3 month period of stimulation in all seven cats. Behavioural responses were able to be elicited reliably and cortical responses were elicited in most animals. The array position within the eye of all seven cats was stable and the devices were tolerated well. Evaluation of the eyes with fundus photography, OCT and ERG did not reveal any evidence of retinal damage.

Conclusions: : Surgical and clinical assessment techniques for an animal model for assessing safety and efficacy of chronic electrical stimulation of the retina by a suprachoroidal array have been developed. The one-piece array and lead wire described is robust and reliable over a 3 month period. The results of this study, including safe stimulation levels will further develop retinal prostheses in humans.

Keywords: retinal degenerations: hereditary • low vision