Argus II Retinal Prosthesis Implantation in a Patient With a History Of Strabismus Surgery:A Surgical Technique

Introduction

The Argus II Retinal Prosthesis System (Second Sight, Sylmar, CA) is the only U.S. Food and Drug Administration-approved prosthesis in the U.S. (Humanitarian Device Exemption approval in 2013).¹ The Argus II is approved for patients with history of retinitis pigmentosa (RP) or outer retinal degeneration with bare or no light perception vision.¹ Long-term studies have demonstrated improved ability to locate objects,^1–3 to detect motion,^1–3 to perform reach and grasp tasks,⁴ improved functional vision,^1–3 and significant improvement in vision-related quality of life with Argus II implantation.⁵

We report a case of a 43-year-old male with end-stage RP and no light perception vision who presented to the USC Roski Eye Institute of the University of Southern California for Argus II retinal prosthesis placement of the right eye. His past ocular history was significant for exotropic strabismus surgery at age 8. Further details about his strabismus surgery could not be obtained. External exam showed a manifest right exotropia.

Technique

The full surgical method for implantation of Argus II retinal prosthesis has been described previously by Humayun et al.² and Ho et al.⁶ Here, we provide a brief description of our modified method for this particular case. After conjunctival peritomy, the extraocular muscles were isolated. Because the lateral rectus (LR) was not initially apparent, exploration was performed. The LR was found 10 mm posterior to its original insertion location consistent with the patient's history of exotropia surgery. Since placement of the coil under the LR, which is critical for the prosthesis stabilization and exposure prevention, was not possible, three 5-0 nylon mattresses sutures were placed temporally anterior to the LR insertion (Figure 1). The anterior bites were made at the original LR insertion with posterior bites 10 mm behind this, creating loops so the scleral band could be passed through them. Once passed through the mattress sutures, the scleral band was fed underneath the inferior and medial recti, allowing temporal placement of the coil underneath the mattress sutures and superotemporal placement of the electronics cases. The other edge of the scleral band was then fed underneath the superior rectus, and the band was secured with the Watzke-Allen sleeve in the superonasal quadrant. The band, suture tabs on the coil, and can of the implant were fixated to the sclera with 5-0 Mersiline sutures (Ethicon, Somerville, NJ). Subsequently, the mattress sutures over the coil were tightened enough to keep the coil in proper position to prevent lifting (Figure 2). The remainder of the surgery was the same as previously described except that at the end, the anterior edge of the coil and overlying sutures were covered with Tutoplast (RTI Surgical, Marquette, MI) (Figure 3). At postoperative month 3, the Argus II implant remained in proper position, and there was no sign of exposure (Figure 4).

Figure 1. Three 5-0 nylon mattress sutures were created temporally in the expected location of the lateral rectus muscle, as depicted above in this patient with retinitis pigmentosa with a history of previous strabismus surgery.

Figure 2. After passage of the scleral band through the mattress sutures and underneath the inferior and medial recti, the coil is shown to be in the correct position and well-supported temporally underneath the mattress sutures.

Figure 3. As shown here, the anterior edge of the coil and overlying sutures were covered with Tutoplast to reduce the risk of postoperative conjunctival erosion and exposure.

Figure 4. At the postoperative month 3 visit, anterior segment slit-lamp photograph of the right eye demonstrates that the Argus II implant is in proper position and that there is no conjunctival erosion and exposure.

Discussion

We describe a modified surgical technique for Argus II implantation in an RP patient with a history of strabismus surgery. Strabismus in patients with RP and other forms of outer retinal degeneration has been described in the literature,^7–9 and knowing how to alter surgical methods to ensure correct positioning of the Argus II implant in these cases is important. In our patient, although the extraocular muscle was not in the expected location, placement of three mattress sutures where the extraocular muscle was expected to be, allowed correct positioning of the coil and scleral band. Proper positioning decreases the chance of serious adverse effects such as conjunctival erosion in the postoperative period.

Exposure of Argus II retinal prosthesis has been described in the literature as the second most common complication and tends to occur over the raised profile of the suture tabs.¹⁰ In a study by da Cruz et al., one patient required explantation of the Argus II retinal prosthesis 14 months after implantation due to recurrent conjunctival erosion with exposure.¹ A second patient had two episodes of conjunctival erosion and the device was re-sutured with closure of the conjunctiva. After experiencing a third episode of conjunctival erosion and exposure, the patient decided to proceed with explantation of the device.¹ Ho et al. noted a 10% rate of conjunctival erosion and 10% rate of conjunctival dehiscence in their cohort of patients at 1-year postoperatively.⁶ They also found that 10% of patients developed presumed endophthalmitis although all cases were culture negative and deemed to be unrelated to preexisting hypotony or conjunctival erosion.⁶ However, it is known that conjunctival erosion and exposure can increase the risk of infection, endophthalmitis, hypotony, and conjunctival inflammation.¹¹ Given that the Argus II is intended to remain in position for decades, it is important to secure the Argus II device in a way that minimizes the chance of exposure and subsequent complications.

We were able to fixate the suture tabs in a way that reduces the chance of exposure by providing additional support with mattress suture placement. If we did not secure the coil with mattress sutures, the coil would have likely slipped from its position intraoperatively, thus preventing proper placement of the tab sutures. In addition, if only tab sutures were to have been placed without mattress sutures, the coil and can would not have been positioned at the proximity of the sclera, resulting in elevation of the implant with subsequent exposure. We also used Tutoplast and half-clear corneas to reduce the risk of device exposure. Using this surgical technique, our patient has no signs of conjunctival erosion or exposure at postoperative month 3 follow-up.

It is not uncommon for patients with RP and other forms of outer retinal degeneration to have had prior strabismus surgery. Therefore, failure of the extraocular muscles to be in their normal anatomic position should be an anticipated surgical challenge in these cases. To overcome this surgical challenge and allow correct positioning of the scleral band and coil, three mattress sutures can be placed at the expected anatomic position of the extraocular muscle to simulate the muscle.