Surgical Implantation of Penetrating Electrode Arrays in Minipig Eyes

Abstract

Purpose: : This work is related to the efforts of the Boston Retinal Implant Project to develop a sub-retinal prosthesis to restore vision to the blind. The specific purpose of this presentation is to develop a safe surgical method to implant a penetrating sub-retinal electrode arrays and to evaluate their biocompatibility.

Methods: : Six Yucatan minipigs were chronically implanted with a passive, penetrating pillar array. Two designs were used in this experiment. Our prototype penetrating pillar arrays used in the first 3 surgeries consisted of a flexible polyimide base with 70 µm tall, SU8 pillars of various diameters ranging from 10 - 80 µm. The pillar arrays used in the second set of 3 surgeries consisted of 112 µm tall SU8 pillars on a 13 µm thick, 1.7mm × 15mm, flexible polyimide base. The pillars were 30 µm in diameter and spaced 200 µm apart, center-to-center. After a partial vitrectomy, a local retinal detachment was created underneath a scleral flap by sub-retinal injection of BSS® and Healon®. The pillar arrays were placed into the subretinal space with the help of an insertion guide.

Results: : Six pillar arrays were implanted into the subretinal space of 6 minipigs. A retinal fold and tear occurred during one surgery; no other surgical complications were occurred in the other 5 surgeries. These pigs were followed for 2 weeks to 7 months. One prototype array tore the retina after 3 months. No funduscopical abnormalities in the other surgeries. Optical coherence tomography (OCT) showed good contact between the array and the retina in 3 animals. Histology from the first 3 pigs showed that the pillars were integrated into the retina with the pillar tips reaching the distal border of the outer nuclear layer.

Conclusions: : Penetrating electrodes can be safely implanted into the subretinal space using our ab externo surgical methods. Penetrating electrodes should lower stimulation thresholds and possibly improve visual results with prosthetic stimulation.

Keywords: retina • vitreoretinal surgery • retinal detachment