Retinal implants: emergence of a multidisciplinary field

Abstract

Purpose of review: This review summarizes the current status of retinal prostheses, recent accomplishments, and major remaining research, engineering, and rehabilitation challenges.

Recent findings: Retinal research, materials and biocompatibility studies, and clinical trials in patients blind from retinitis pigmentosa are representative of an emerging field with considerable promise and sobering challenges. A summary of progress in dozens of laboratories, companies, and clinics around the world is presented through a synopsis of relevant studies, not only to summarize the progress but also to convey the remarkable increase in interest, effort, and outside funding this field has enjoyed.

Summary: At present, clinical applications of retinal implant technology are dominated by one or two groups/companies, but the field is wide open for others to take the lead through novel approaches in technology, tissue interfacing, information transfer paradigms, and rehabilitation. Where the field will go in the next few years is almost anybody's guess, but that it will move forward is a certainty.

1

The Argus II epiretinal implant system (Second Sight Medical Products Inc., Sylmar, California, USA, www.2-sight.com). The implanted system consists of a scleral band containing the secondary coil receiving the RF signal carrying power and data, and a hermetic capsule containing electronics to demultiplex data for the 60 implanted electrodes; and a ribbon cable passing through the sclera and leading to the 6_10 electrode implant, held in place over the macular area by a single retinal tack.

2

The Alpha IMS subretinal implant system (Retina Implant AG, Reutlingen, Germany) www.retina-implant.com. A. Lower left: subretinal chip with 1500 photodiodes, amplifiers and electrodes, on a subretinal polyimide foil, connected intraorbitally to the subdermal power cable that ends in a secondary coil encapsulated in a ceramic housing under the skin behind the ear. The silicone patch covers the exit of the foil trough choroid and sclera near the temporal equator of the eye. The reference electrode is placed near the orbital rim. Enlarged chip and unit cells are shown in center. B: Sketch of the subdermal power supply cable and secondary coil (white) in a patient. The external primary coil (black) receives power and control signals from a control box operated by the patient; the coil provides inductive transdermal transmission and is kept in place by magnetic force. Insert: fundus photo with the implant under the translucent retina next to the optic nerve head; implant field of view is 11° × 11° (provided by Eberhart Zrenner[37]).

2

The Alpha IMS subretinal implant system (Retina Implant AG, Reutlingen, Germany) www.retina-implant.com. A. Lower left: subretinal chip with 1500 photodiodes, amplifiers and electrodes, on a subretinal polyimide foil, connected intraorbitally to the subdermal power cable that ends in a secondary coil encapsulated in a ceramic housing under the skin behind the ear. The silicone patch covers the exit of the foil trough choroid and sclera near the temporal equator of the eye. The reference electrode is placed near the orbital rim. Enlarged chip and unit cells are shown in center. B: Sketch of the subdermal power supply cable and secondary coil (white) in a patient. The external primary coil (black) receives power and control signals from a control box operated by the patient; the coil provides inductive transdermal transmission and is kept in place by magnetic force. Insert: fundus photo with the implant under the translucent retina next to the optic nerve head; implant field of view is 11° × 11° (provided by Eberhart Zrenner[37]).