39
QUESTION
WHAT IS THE ARTIFICIAL RETINAL PROSTHESIS (ARGUS II IMPLANT) AND WHO WOULD BE A GOOD CANDIDATE FOR IT?
Paul Hahn, MD, PhD
The Argus II retinal prosthesis is an implant designed to restore visual stimulation previously considered permanently lost. It is the only retinal prosthesis currently approved by the US Food and Drug Administration (FDA; 2013). It has additionally received the Conformité Européenne (CE; 2011) mark and has been approved by Health Canada (2015). The Argus II includes an external (wearable) and internal (surgically implanted) component. The external equipment consists of glasses, a video processing unit (VPU), and a wired cable (Figure 39-1A). The glasses hold a video micro-camera in the nasal bridge that transmits images to the wired VPU for image processing. The VPU transforms the images to data that are then transmitted wirelessly to the internal implant in the eye, which also receives power wirelessly via induction from the external hardware.
The implanted component consists of a receiving coil and electronics case secured to the eye in a scleral buckle fashion and a 60-electrode array secured to the inner surface of the retina with a retinal tack (Figure 39-1B). The data sent from the external VPU wirelessly to the implanted electronics package stimulates the array to emit small pulses of electricity that excite remaining viable inner retina cells, including ganglion cells. These artificially stimulated retinal ganglion cells transmit signals through their axons to the lateral geniculate nucleus and then the occipital cortex, which perceives patterns of light. The final step is for patients to piece together these patterns of light to form vision.1
When I evaluate a patient interested in this technology, I first confirm that they fit the approved indications. The Argus II is currently FDA-approved for a defined subset of patients: adults (age 25 years or older) with a diagnosis of retinitis pigmentosa (RP) and a history of prior useful vision who have progressed to bare or no light perception vision in both eyes. Although I tell patients that other diseases may also benefit from the Argus II, the only on-label indication is currently for end-stage RP. Contraindications include comorbidities that would prevent the implant from functioning properly (eg, optic nerve disease, cortical blindness, prior retinal detachment, retinal vascular occlusion, trauma, and severe strabismus). Other contraindications include conditions that would prevent adequate implantation of the Argus II, such as conjunctival thinning, axial length less than 20.5 mm or greater than 26 mm (given the fixed intraocular cable length), and conditions that prevent implant visualization, such as corneal opacities. Phakic patients will also require removal of the lens prior to or during Argus II implantation. Finally, the implant is not recommended in patients with a tendency to eye rubbing or with a metallic or active implantable device in the head, such as a cochlear implant.
Figure 39-1. Argus II retinal prosthesis components. (A) Diagram of external portion including glasses with micro-camera, wireless transmitter (radio frequency coil), and VPU (Reprinted with permission from Second Sight Medical Products, Inc.). (B) Diagram of the surgically implanted component including the electronics case, the wireless antenna, and the 60-electrode array (Reprinted with permission from Second Sight Medical Products, Inc.) with photograph identifying an Argus array optimally centered on the macula and attached to the retina by a retinal tack (image courtesy of Paul Hahn, MD, PhD).
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