Even while the majority of retinal prostheses are still in the research stages, they are becoming more widespread in the United States and internationally.
The only retinal prosthesis approved in the U.S. is the Argus II retinal prosthesis system (Second Sight Medical Products, Inc., Sylmar, CA, USA). It was approved by FDA in 2013 as a humanitarian use device as the result of the Argus II clinical feasibility trial. As of this year, over 300 Argus II retinal prosthesis surgeries have been performed worldwide.
Argus II is currently indicated for patients with a clinical diagnosis of retinitis pigmentosa and bare light perception vision or worse. Patients with retinitis pigmentosa are born with normal vision and gradually lose their vision over time, with severe cases resulting in total blindness and the inability to discern light. Argus II provides patients with improvements in vision and resultant improvements in activities of daily life, social interactions, quality of life, and orientation and mobility. After the FDA approval, the post-approval study was initiated to monitor of serious adverse events in Argus II recipients.
At the recent annual meeting for the American Society of Retina Specialists held in Vancouver, Canada, the post-approval study investigators presented on the complication profile of the Argus II recipients in a talk entitled “Argus II Retinal Prosthesis Complication Profile Pre- and Post-FDA Approval.”
To achieve the study goal, the authors compared the serious adverse events seen at one and two years in the Argus II clinical feasibility trial and the Argus II post-approval study. The Argus II clinical feasibility trial was the pivotal trail of 30 subjects that outcomes of which resulted in Argus II FDA approval.
Those results have been extensively published with outcomes available up to five years of follow-up. A total of 53 patients have been enrolled in the post-approval study. Of those, 32 and 21 have so far completed the one and two year follow-up, respectively. The main goal of the presentation was to examine if the type or incidence of complications have changed now that there are multiple surgeons with different experience levels implanting Argus II in a diverse number of settings.
The Argus II surgery is performed by trained vitreoretinal surgeons and is longer than the majority of standard retinal surgeries. If the patient is phakic, they are rendered aphakic. Otherwise, the intraocular lens is kept in the eye. The surgery involves implantation of Argus II external and internal components. The receiving coil and the electronics case are sutured to the bare scelra. A vitrectomy is performed and a 5.2mm sclerotomy is created to insert the electrode array into the mid vitreous cavity. The array is placed over the macula and secured using a retinal tack that penetrates the retina, the chorid, and the sclera. All sclerotomies are sutured and confirmed to be watertight. Allograft is secured externally over the array cable, electronics case suture tabs and receiving coil tab. The Tenons and conjunctiva are brought forward and re-approximated to the limbus.
In terms of serous adverse events, there were no cases of endophthalmitis, Argus II explantation, or re-tacking in the post-approval study. On the other hand, three cases of endophthalmitis, one case of explantation, and two cases of re-tacking were seen in the clinical feasibility trail. Of note, there were three cases of vitreous hemorrhage in the post-approval study and none in the clinical feasibility trial.
Given the amount of the hardware that is secured to the sclera, conjunctival erosion has been a concern in Argus II surgery. It was seen in three subjects in the clinical feasibility trial and in two in post-approval study.
The large sclerotomy is needed to introduce Argus II array into the vitreous cavity. Thus, post-operative hypotony is also a concern in these patients. It was seen in two subjects in both cohorts.
Hyloid in patients with retinitis pigmentosa can be very adherent to the retina. There were two cases of retinal detachment (rhegmatogenous, tractional, or serous) in the clinical feasibility trial and one in the post-approval study.
Argus II retinal prosthesis surgery provides new vision to patients who have lost all functional vision. The patients undergo extensive rehabilitation after Argus II implantation to learn how to interpret visual phosphenes as vision. Although Argus II does not restore vision lost due to retinitis pigmentosa, the patients are able to enjoy increased independence, social inclusion, and improved safety in their daily activities.
Understanding the complication profile is essential as more practitioners are implanting the device. Overall, the authors concluded that the complication profile remains acceptable up to 2 years post-operatively as site diversity increases and more surgeons implant the Argus II post-FDA approval. Additional outcomes will be forthcoming as more patients complete longer follow-up.
Dr. Aleksandra Rachitskaya is a vitreoretinal surgeon at Cole Eye Institute, Cleveland Clinic, and an assistant professor of Ophthalmology at Cleveland Clinic Lerner College of Medicine of Case Western Reserve University. She is a consultant to Alcon, Allergan, and Zeiss and reports no relevant financial disclosures.