Post-surgical findings in 10 rabbits implanted with the VLARS (Very Large Array Retina Stimulator) device in two shapes over a period of 12 weeks

Abstract

Purpose: Over the last years noteworthy improvements in visual prosthetics have been achieved but restoring a substantial visual field is yet a task to be accomplished. Our research group created a large stimulation array with a 12mm diameter covering 37.6° visual angle and mounting 250 individual electrodes to address this problem. In an animal trial study two different shapes of these arrays have been implanted into 10 rabbits in order to observe the surgical outcome and biocompatibility.

Methods: 10, 4 to 6 months old rabbits (4 albino, 6 pigmented) were implanted with the VLARS-device through vitreous surgery. Post-surgery examinations were performed 1 day, 1 respectively 2, 4, 6, 8 and 12 weeks after surgery and included clinical examination, funduscopy, OCT (optical coherence tomography) and ultrasound imaging. Finalization took place after the 12th post-surgical week. The implanted eyes were enucleated and underwent histological examination in order to observe damage or cellular immigration.

Results: During surgery 3 eyes experiences retinal detachment which lead to the termination of the implantation in one animal. At least 2 eyes experienced noteworthy intra-vitreal bleeding which was being staunched during surgery. Due to the corneal incision, damage occurred and corneal blur rendered optical examination impossible in most animals during the first weeks after surgery. After application of steroids, imaging could be performed showing an overall positive outcome in terms of long-term compatibility. No cellular immigration, additional retinal detachments or other adverse events were observed, the arrays stayed fixated at implantation site. A gap between the stimulator array and the retinal surface enlarging towards the periphery has been unmasked. Histologic examination showed expected mild gliosis in the area of retinal fixation.

Conclusions: The long-term implantations showed no adverse effects on behalf of the used materials. The surgical process, and especially the trans-corneal Insertion caused damage on the cornea. This was improved by using different techniques of corneal insertion in order to minimize the incision’s size. The vitreous surgery itself and the fixation of the array regularly healed off. To establish a closer contact between the array and the retina additional ways of fixation have to be introduced in the study.