35 Ab Interno Suprachoroidal Shunts: CyPass and iStent Supra A 70-year-old man is referred for evaluation of his cataracts and glaucoma. A combined procedure is recommended by his referring physician. The patient frequently travels from the United States to the Middle East and France, and often forgets to take his eyedrops. His vision is 20/40 OD and 20/30 OS and his visual fields demonstrate an early superior nasal step defect in the right eye and are full in the left eye. Optical coherence tomography (OCT) shows mild thinning inferiorly in the left eye and inferior temporal thinning consistent with his visual field defect in the right eye. The patient’s intraocular pressure (IOP) is 18 mm Hg OD and 15 mm Hg OS on latanoprost in both eyes and brinzolamide in the right eye. The patient’s goal is to have a lower IOP in the right eye and to perhaps get off at least one medication in each eye; however, he does not wish to have the long-term risk of infection associated with conventional trabeculectomy. He chooses to undergo cataract extraction with intraocular lens placement combined with a suprachoroidal stent, first in the right eye and then in the left. Four to 6 weeks after surgery in both eyes, his visual acuity is 20/20 OU without correction and the IOP is 14 mm Hg OU. He is on latanoprost in the right eye only, and he is considered to be at target IOP. In the past there has been a significant disparity identified for the timeline of transitioning from glaucoma medications to the incorporation of incisional procedures in the treatment of glaucoma. Often conventional procedures, such as trabeculectomy and shunt implants, must be reserved for more severe and end-stage glaucoma patients who have reached the point of being intractable to medication management. The reason for such restraint has come about as a result of research on the risk profile that is associated with these invasive procedures, reporting case complication rates of 39 to 60%.1 Given this knowledge, recent research efforts have focused on the need to develop a minimally invasive intervention for providing effective IOP control in patients with mild to moderate glaucoma. Supraciliary implants have been an area of intensive study within minimally invasive glaucoma surgery (MIGS) and provided great improvements in the efficacy of glaucoma treatment. These implants are among a variety of such devices currently being investigated in U.S. Food and Drug Administration (FDA) trials for safety and effectiveness. The underlying mechanism of such a device lies in accessing the suprachoroidal space and capitalizing on the uveoscleral flow as a means of reducing the IOP. This chapter provides a framework for understanding the research into this device and that prospective benefits that it has the potential to offer as a modality for future MIGS treatment. The CyPass micro-stent (Transcend Medical Inc., Menlo Park, CA) is a tube-shaped, supraciliary implant that acts as a conduit to the suprachoroidal space. It is made of biocompatible, nondegradable polyimide material. The device size measures 0.51 mm in external diameter and 0.30 mm in internal diameter, and 6.35 mm in length. The surface of the device distal to a prominent collar marking on the proximal end is accented by a fenestrated surface of 76-µm diameter pores along this length that aid in longitudinal and circumferential dispersal of drained aqueous humor from the anterior chamber into the suprachoroidal space.2–4 A similar suprachoroidal micro-stent currently undergoing evaluation is the iStent Supra (Fig. 35.1), (Glaukos, Laguna Hills, CA), which is implanted in much the same manner that the CyPass is placed. Both of these ab interno supraciliary micro-stents are currently under investigation in the United States in eyes with mild-to-moderate primary open-angle glaucoma at the time of cataract surgery. These devices potentially offer benefit in more advanced glaucomatous disease and may eventually play a role in angle-closure glaucomas. Uveoscleral outflow is estimated to account for roughly half of the aqueous drainage in normal human eyes.3 Physiology studies have identified a gradient of negative pressure within the suprachoroidal space that serves as the conduit for this aqueous flow pathway.2,3 This gradient has been measured at –0.8 ± 0.5 mm Hg between the anterior chamber and the perilimbal portion of the suprachoroidal space with deeper compartmental sections near the optic nerve decreasing to around –3.7 ± 0.4 mm Hg.2 An understanding of the potential for this physiological pathway as a diversion for aqueous flow release in situations of elevated IOP is not new to the field of glaucoma surgery. Yet the minimally invasive ab interno approach offered by devices such as the iStent Supra or the CyPass micro-stent is a softer approach than has previously been attempted. The ab interno technique has permitted minimization of trauma to tissues during device implantation and has helped to avoid the detrimental fibroblastic proliferative response that had plagued the long-term results of earlier ab externo techniques.2 Fig. 35.2 Anatomic illustration for the proper placement of the CyPass micro-stent. (Courtesy of Steven Vold, MD.) Studies thus far examining the safety and efficacy of the suprachoroidal stenting have selected patients based on criteria of uncontrolled (IOP ≥ 21 mm Hg) open-angle glaucoma (OAG) in contexts both with and without medication use.1,3 CyPass has also been implemented in studies of patients who desired to reduce dependency on medications for already-controlled IOP.1 Performing the CyPass procedure in patients concomitantly undergoing phacoemulsification has also been implemented and demonstrated great success (COMPASS, unpublished data). A patient history of prior glaucoma surgery does not preclude the possibility of utilizing a CyPass implant for further pressure control, nor does CyPass implantation prohibit performing further surgery, if needed, for IOP control.1 Studies of the iStent Supra are currently ongoing, but it is expected that the results will be similar. The supraciliary implant is inserted via an ab interno approach that is facilitated through a 1.5- to 2.0-mm clear corneal incision. A standard clear corneal cataract incision may also be utilized.1,2 Obtaining the correct insertion angle for this micro-stenting procedure is assisted by the use of an ophthalmic viscosurgical device to slightly overfill and thereby deepen the anterior chamber.2,5 The use of viscoelastic further serves the purpose of protecting the corneal endothelium during micro-stent delivery.2 Device insertion is aided by the use of a curved delivery tool with a retractable guidewire.2 The base of the scleral spur serves as a critical landmark in targeting the device for successfully accessing the suprachoroidal space. To perform this, the tip of the guidewire must be engaged with the iris root and subsequently passed into the suprachoroidal space.1 In addition to proper intracameral preparation and insertion technique, the appropriate positioning of the operating microscope, aided by using a gonioprism, is necessary for visualization of the implant site. By rotating the microscope 30 to 40 degrees away from the operator as well as a tilting the patient’s head an equivalent angle away, the best possible view of the operating site is achieved. The addition of viscoelastic to the surface of the cornea further serves as an interface for improvement of the image quality provided by the approximated goniolens.2 The final appearance of the micro-stent after device insertion should demonstrate a single ring exposed at the proximal end of the device resulting in 1.0 mm of exposed implant (Fig. 35.2). To determine proper positioning, the device should be observed with its exposed end residing between the pigmented trabecular meshwork and Schwalbe’s line.2 Once ascertainment of final positioning is made, an evacuation of viscoelastic should be performed using irrigation and aspiration followed by corneal wound closure by either the hydration technique or the use of a single interrupted suture.2,3 Postoperative assessment of device placement can be performed by gonioscopy (Fig. 35.3), optical coherence tomography, or ultrasound bimicroscopy.3,4
Case Presentation
The Procedure
Device Description
Rationale Behind the Procedure
Patient Selection
Surgical Technique
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