A Suprachoroidal Retinal Prosthesis Is Safe In A Chronic Implantation Model

Abstract

Purpose: : To assess the safety of a suprachoroidal retinal prosthesis in chronic implantation.

Methods: : A medical grade silicone/Pt electrode array with a fully implantable lead wire was implanted into the suprachoroidal space in one eye of each normal-sighted adult cat (n=8); the contralateral un-operated eyes were used as controls . Animals were followed up for 3 months, then transcardially perfused with paraformaldehyde; eyes were post-fixed in Davidson’s solution, dissected into representative strips, processed and assessed by a pathologist. Studies were conducted in accordance with ARVO ethics guidelines.

Results: : Following chronic passive implantation, the array was located within the suprachoroidal space, the sclera was not deformed by the electrode and the retina was not detached. Initial retinal and suprachoroidal oedema typically resolved within 2 weeks leaving an undisturbed retinal surface. The foreign body response was minimal with sparsely distributed macrophages and giant cells surrounding the electrode cavity. There were no signs of haemorrhage or ongoing inflammation, and no polymorphonuclear leukocytes. A narrow sheath of fibrous tissue had developed around the implant (mean: 17µm±7µm SD) and dense melanin granules had accumulated within choroidal macrophages in isolated areas near the electrode. These pigmented regions corresponded with dark areas of fundus images. All sections were negative for bacterial or fungal infections. A mid-grade granuloma surrounded the lead with ongoing inflammation, encapsulated by thicker fibrosis (300µm - 2mm). Haemosiderin was detected in tissue surrounding the lead region indicating a prior bleed, consistent with movement based irritation. In vivo eye movement was not restricted in forced duction tests.

Conclusions: : Results show that a suprachoroidal retinal prosthesis was safe and well-tolerated for 3 months post implantation.

Keywords: pathology: experimental • wound healing • choroid