A Suprachoroidal Retinal Prosthesis with a Flexible Lead is Reliable for Patient Testing

Abstract

 

Purpose

 

A flexible intraorbital lead was developed to minimise risk and simplify implantation of a retinal prosthesis. The microwire based prosthesis was tested in a preclinical model, then optimised in cadavers and tested in a clinical pilot study.

 

Methods

 

Initially, a suprachoroidal (SC) electrode array was developed with a transscleral lead of 14-22 platinum microwires in silicone. It was implanted in cats (n = 16) for 3 months. The lead was sutured on the sclera with a silicone patch and tunnelled under conjunctiva to a patch on the orbital rim. It followed either a straight path (3 implants) of 12 mm; or a curved path (13 implants; Fig. 1) of 16 mm with 1 mm strain relief cones. Histological assessment was performed on the tissue around the lead. The lead routing was then fitted to a human orbit and tested in cadavers. This lead, with strain relief cones, was 34 mm to the lateral orbit where it was fitted inside a channel. Lead durability was then tested in a mechanical model of a skull and eye moving to 25° of abduction/adduction. A 24-channel electrode array with optimised lead and a percutaneous connector (on the parietal bone) was then implanted in a clinical pilot. The lead location was monitored with X-ray and CT imaging.

 

Results

 

The SC implant and orbital lead were well tolerated in all 16 cat eyes, with no conjunctival or skin erosion around the eye. From 197 individually wired electrodes with a curved lead, 177 were connected following 3 months of implantation; which contrasted with 24 connected out of 36 implanted using a straight lead (Chi-square P < 0.001). Implant and lead were stable in all but one case where the implant’s anterior end eroded the sclera. The typical tissue response around the moving lead was a thick granulomatous fibrous capsule. The leads in mechanical durability testing have undergone 65 million eye movements with no wire breakages. In humans, the implant with intraorbital lead was stable during the initial 6 months of implantation (Fig. 2). All the electrodes remained connected.

 

Conclusions

 

The SC retinal implant with flexible lead allowed for minimal surgical manipulation of the eye and distal placement of larger components. The strain-relieved lead was reliable during chronic implantation in a preclinical model and in a clinical pilot.

 

 

Fig 1. Suprachoroidal implant with curved lead for cat

 

 

Fig 2. CT scan of patient with retinal prosthesis and strain-relieved lead (blue)

 

Keywords: 762 vitreoretinal surgery • 688 retina • 631 orbit