The Surgical Approach and Clinical Assessment of Chronic Implantation of a Wide-Field Suprachoroidal Array in a Feline Model

Abstract

Purpose: : To develop a surgical approach to implant a wide-field suprachoroidal array and assess it's safety over three months with clinical follow-up using OCT and ERG in a feline model.

Methods: : Adult normally sighted cats (N=8 ) were implanted with a suprachoroidal electrode array and lead wire / connector. Fellow eyes were used as control eyes. The surgical approach involved both the insertion of the array into the suprachoroidal space and the implantation of the lead wire into a subcutaneous pocket. The cats were monitored clinically, photographed, OCT imaging was used to assess the area centralis and the electrode array, and retinal function was assessed using full field ERG. At the end of three months, the lead wire was exposed, impedances measured and electrically evoked responses were measured within the occipital cortex.

Results: : The array was able to be placed in the suprachoroidal space in all cases. Postoperatively one cat at day three developed a large suprachoroidal haemorrhage with consequent reduction in ERG which improved as the haemorrhage resolved over twelve weeks. One cat developed mild suprachoroidal haemorrhage at day one and overlying retinal folds which subsequently settled over six weeks. One cat developed breakdown of the wound over the lead at week ten, just prior to the terminal acute experiment. After three months all cats remained with the array in situ amd no infections developed within the eye or the subcutaneous pocket. Electrically evoked responses were reliably obtained in all eight cats with stimulation thresholds similar to those seen in acute suprachoroidal stimulation.

Conclusions: : An electrode array can be safely placed in the suprachoroidal space in cats for a three month period with excellent anatomical results as shown with OCT, and functional results as demonstrated by ERG. Electrical stimulation at the end of this time results in reliable electrically evoked responses within the occipital cortex. These results provide enough evidence to continue with this approach for a long term wide view array for human implantation.

Keywords: retina • electroretinography: non-clinical • low vision