Extraocular Surgical Approach for Placement of Subretinal Implants in Blind Patients: Lessons from Cochlear-Implants

Abstract

In hereditary retinal diseases photoreceptors progressively degenerate, often causing blindness without therapy being available. Newly developed subretinal implants can substitute functions of photoreceptors. Retina implant extraocular surgical technique relies strongly on cochlear-implant know-how. However, a completely new surgical approach providing safe handling of the photosensor array had to be developed. The Retina Implant Alpha IMS consisting of a subretinal microphotodiode array and cable linked to a cochlear-implant-like ceramic housing was introduced via a retroauricular incision through a subperiosteal tunnel above the zygoma into the orbit using a specially designed trocar. Implant housing was fixed in a bony bed within a tight subperiosteal pocket in all patients. Primary outcomes were patient short term safety as well as effectiveness. Nine patients participated in the first part of the multicenter trial and received the subretinal visual implant in one eye. In all cases microphotodiode array pull-through procedure and stable positioning were possible without affecting the device function. No intraoperative complications were encountered. The minimally invasive suprazygomatic tunneling technique for the sensor unit as well as a subperiosteal pocket fixation of the implant housing provides a safe extraocular implantation approach of a subretinal device with a transcutaneous extracorporeal power supply.

Figures

Figure 1

The Retina Implant Alpha IMS consists of the vision chip (multiphotodiode array, 4 pixels magnified in the center) on a polyimide foil (PI-foil, both placed subretinal) and a power supply cable connecting the microchip with the receiver coil in a ceramic housing and the reference electrode placed subdermally at the temple and retroauricular region.

Figure 2

(a) The implant's core is the light sensitive subretinal chip with 1500 pixels. The chip size is approximately 3 mm × 3 mm; it is approximately 70 μm thin when placed on a polyimide foil (thickness approx. 20 μm) with gold connective wire prints, which leaves the subretinal space in the upper temporal periphery through the choroid and the sclera. (b) Fundus image of the Retina Implant Alpha IMS.

Figure 3

Illustration of the subdermal placement of the receiver coil and the power supply cable (white/grey) in relation to the epidermal transmitter coil (black) and cable leading to the power supply in the patient's pocket.

Figure 4

Illustration of the curved retroauricular incision following approximately the helix of the pinna (1) leaving the fascia of the temporal muscle intact. A second horizontal incision (2) was placed along the caudal limit of the temporal muscle crossing nearly perpendicularly the primary skin incision and providing a stabile two-layer wound closure.

Figure 5

The periost layer was elevated exposing the bone at the sutura frontozygomatica. At this point an L-shaped canal was drilled, providing flexible stability and optimizing angulation for the cable entering the orbit.

Figure 6

A custom made hollow trocar was advanced from the periorbital region subperiosteally to the retroauricular area. The cone end of the trocar was removed and the sensitive implant chip was placed inside the trocar tube. Retracting the trocar with the implant chip allowed safe passage of the subperiosteal tunnel.