The Argus II system (Second Sight Medical Products, Sylmar, CA) provides functional vision for people with severe vision loss due to outer retinal degeneration. A video camera in the patient's glasses is combined with a video processing unit (VPU) and the implant itself; the antenna and electronics are placed on the globe with an encircling band, whereas the electrode array is implanted epiretinally. The information captured by the camera is transmitted to the VPU, down-sampled, processed, and wirelessly transmitted to the epiretinal electrode array, which emits electrical pulses to stimulate the remaining retinal cells. Worldwide, 170 implantations have been performed, four of which took place in our clinic. Five explantations have been reported due to medical reasons;1–3 however, no re-implantation has been described. This is the first case report of an explantation and a simultaneous re-implantation of an Argus II system showcasing the technical and surgical development in modern ophthalmology.
A 59-year-old Caucasian woman with retinitis pigmentosa underwent implantation of an Argus II system without complications. Postoperatively, the electrode array was well placed and functioned well. Perceptual threshold measurements with a custom developed software showed that nine electrodes worked with thresholds less than 233 μA and 23 electrodes with thresholds greater than 233 μA and less than or equal to 677 μA.
In the course of postoperative rehabilitation, multiple tests and trainings were performed and confirmed a good function. The number of electrodes working with low threshold increased over the first 12 months, and the function test showed constantly a good function (Table 1).
Perceptual Thresholds And Results of Square Localization and Direction of Motion Tests at 3, 6, and 12 months as well as 5 Months Post-Explant/Re-implant Surgery
However, 7 months following implantation, the patient reported progressive heat generation from the glasses in the region of the antenna when using the system. After 12 months, the heat sensation had increased to an unbearable extent, and the patient could no longer use the prosthesis. A self-test program pointed to the existence of a breach in the insulation of the antenna creating a decline in the radiofrequency link necessary to power and command the implant. The video processing unit (VPU) logs diagnostic information about the implant each time the VPU is turned on. Review of diagnostic data from this patient's VPU revealed voltage readings indicating that the coil's insulation could be compromised, leading to current leakage from the coil windings through the insulation to the body fluid and causing a decline in the radiofrequency link.
Due to the initial satisfaction and high motivation of the patient, who emphasized the relevant benefit from the device during the past months, the patient and the medical team decided to strive for an implant exchange although this had never been performed before.
Explantation of the entire system, including all intra- and extraocular components and the re-implantation of a new device, took place without complications and lasted 4 hours (in comparison, duration of the prior implantation was 2:05 hours). Although uneventful, several critical steps could be identified that are specifically related to an implant exchange and therefore are important to consider for future surgeries.
Firstly, the conjunctiva was severely scarred all around the globe (Figures 1a–1c). Especially above the scleral patch, the adhesion was very strong. It is essential to perform peritomy without tissue loss to entirely cover the new implant with conjunctiva.
Intraoperative setting with critical steps and pifalls. (a) Eye before explantation. (b–e) Peritomy with conjunctival scarring and encircling band overgrown by fibrotic tenon. (f) First electrode array before explantation. (g–i) Explantation of the old array. (j–k) Implantation of the new system. (l–m) New array is fixed with retinal tack. (n–o) Sclerotomy is sewed and covered with a Tutopatch. (p) Eye at the end of surgery.
The band encircling the globe and the extraocular components, antenna, and electronic case were overgrown by fibrotic tenon tissue (Figures 1d and 1e). The entire capsule including submuscular parts had to be meticulously removed before extraction.
Another demanding step was the preparation of the 5-mm sclerotomy for cable entrance into the globe (Figures 1g and 1h). The sclerotomy showed extensively macerated edges, which could not be sutured properly. This led to an increased risk for postoperative hypotonia (Figures 1n and 1o).
The extraction of the former electrode array was more difficult than assumed (Figures 1f–1h). The special design of the barbed tack adhering to the sclera requires a relevant force for extraction (Figure 1f). In our case, it succeeded with some resistance but without the occurrence of choroidal hemorrhage or circumscribed retinal detachment.
After the extraction, the underlying retinal surface disclosed a fibrotic, hollow-like, plaster cast that could not be removed. As such, the new electrode array had to be placed in almost exactly the same position. The new retinal tack was also fixed in the same place (Figures 1l and 1m).
Immediately after the Argus II explant procedure, the surgeon performed a new Argus II implant standard procedure with the same surgical tools and suture materials. The only difference between the initial implantation was the vitrectomy step. During initial implantation the surgeon performed a core vitrectomy and triamcinolone suspension was injected into the mid-vitreous cavity to help the surgeon perform an accurate removal of the strongly adherent posterior hyaloid membrane.
During re-implantation, the posterior hyaloid removal was not necessary, and this significantly reduced the surgical time to perform the vitrectomy step.
The intraoperative steps can be followed more closely in our video (see Supplemental Video below).
During postoperative assessment, the implant was well-placed, the retina was stable, and no hemorrhage was observed. Intraocular pressure (IOP) was low but stable. On the second day, a severe hemorrhagic choroidal detachment occurred with a consecutive increase of IOP. We decided to lower the pressure via topical and oral therapy and to await resorption. The situation improved continuously and 3 months later, the hemorrhage was totally absorbed, the pressure normal, and the electrode array in place and functional.
After 5 months, the number of singles electrodes yielding a perception with low threshold current was even improved compared to the prior implant. Imaging showed a fibrotic dome above the electrode array (Figures 2, 3, and 4). Visual perception performed within an average scope (Table 1).
Fundus picture of the new chip showing the vascularized fibrotic capsule above the electrode array.
In comparison: Fundus picture of the first chip, which did not show fibrosis.
Optical coherence tomography (OCT). (a) Shows the first chip; (b) the new chip. Because of a vascularized fibrotic capsule above the new chip, OCT quality is limited.
The explanted device was analyzed at Second Sight Medical Products. Visual inspection of the device revealed no signs of corrosion, damage, or material failures on either the implant electronics package, the array, or the tack. Post-explant analysis revealed that the coil insulation at the points of the breach was thin, which was due to a manufacturing defect in which a silicone insulating sheet was not included in the coil subassembly. As a result of this analysis, quality control measures were instituted to prevent recurrence of this manufacturing defect.
This is the first case report of a one-step exchange of the Argus II system and shows the feasibility of this complex procedure, raising hope for patients in whom the implant initially achieved a good performance but failed later on because of technical problems. We have identified several critical surgery steps that might be important for other surgeons with similar cases.
In our patient, the imprint of the former array, which was overgrown by fibrotic tissue, limited the array relocation. In contrast, de Juan et al. reported three cases where relocation was feasible without any limiting fibrosis.3 In conclusion, the extent of fibrosis should be taken into consideration during preoperative planning.
The tack can be removed without directly inducing a hemorrhage, but the risk of a suprachoroidal hemorrhage persists even after days, especially in combination with postoperative hypotonia (due to defective water-tightness of the sclerotomy).4 Therefore, achieving water-tightness around the re-opened sclerotomy is essential.
Interestingly, the new array showed better threshold function than the prior implant. The fibrotic encapsulation above the implant might act as insulation towards the vitreous yielding more current to the retinal cells. A similar phenomenon is described in neurosurgery where glial scarring around implants causes an insulation of the electrodes.5
This case report demonstrates the feasibility of an exchange of an Argus II. However, challenging factors such as hypotonia and hemorrhage as well as potential fibrotic scarring complicating the reposition of the chip have to be taken into account.