Suprachoroidal Shunt: SOLX Gold Shunt

34 Suprachoroidal Shunt: SOLX Gold Shunt

Jessica E. Chan and Peter A. Netland

Case Presentation

A 72-year-old woman with advanced primary open-angle glaucoma was referred after placement of an EX-PRESS Glaucoma Filtration Device (Alcon, Fort Worth, TX) under the conjunctiva, without a partial-thickness scleral flap. The patient had noted blurry vision and discomfort in the left eye. She was functionally monocular, having lost central vision in the right eye due to glaucoma.

On examination, the vision was CF (counts fingers) OD and 20/200 OS. The intraocular pressure (IOP) was 15 mm Hg OD and 32 mm Hg OS. She had been using brinzolamide in both eyes b.i.d., bimatoprost in both eyes at bedtime, and Combigan in both eyes b.i.d., and was previously treated with a laser trabeculoplasty. The EX-PRESS implant had eroded through the conjunctiva, but there was no aqueous leak. The superior conjunctiva surrounding the device was immobile. There was focal hyperemia around the device. There was mild corneal edema, the anterior chamber was deep, the posterior chamber intraocular lens was centered, and there was advanced cupping of the disk with a grossly normal macula. Previous automated perimetry (Humphrey visual field, Swedish Interactive Threshold Algorithm [SITA] Standard, 30–2) had shown apparent loss of central fixation in the right eye with a central island of vision in the left eye, and a mean defect of –31.11 OD and –26.74 OS. Her previous best-corrected vision was 20/40 OS.

Because of the conjunctival scarring and erosion, the options for transscleral filtration were limited. The patient was treated with removal of the EX-PRESS device, closure of the fistula, debridement of the area, and closure of the conjunctiva, followed by implantation of a SOLX Gold Shunt (SOLX Inc., Waltham, MA) in the temporal quadrant. The IOP was 4 to 6 mm Hg in the immediate postoperative period, with no formation of choroidal effusions. After the first week, the IOP increased to the low teens. After several months, the IOP increased to the high teens and the patient was treated with digital massage and medical therapy. Over a period of several months, her best-corrected vision in the left eye returned to 20/40, which was her baseline vision (Fig. 34.1).

The Procedure

The above case is an example of the use of the SOLX Gold Shunt in a patient with advanced open-angle glaucoma refractory to primary glaucoma surgery. In addition to use as a secondary or tertiary procedure for glaucoma, the device potentially may be used for primary surgical treatment of glaucoma not responsive to medical or laser therapy. The SOLX Gold Shunt is a suprachoroidal shunt, designed to drain aqueous humor from the anterior chamber into the suprachoroidal space, with eventual drainage through the uveoscleral outflow pathway, obviating the need for a bleb. It has been approved for usage in Canada and CE Mark countries in Europe, and is currently under investigation in a Food and Drug Administration (FDA) multicenter clinical trial in the United States. It is a 24-karat-gold, nonvalved, flat-plate drainage device that has been found to be biocompatible and inert in the eye.1

The current model of the SOLX Gold Shunt is the third generation of the device; it became commercially available in 2010. The device is ~ 80 µm thick, weighs 9.2 mg, and is 5.5 mm long, with a 3.2-mm anterior width and a 2.1-mm posterior width. Previous versions of the device contained channels to direct aqueous flow and were primarily used to study safety. Previous versions of the device were called GMS (Gold Micro Shunt) and GMS+, whereas the current commercial device is simply called the SOLX Gold Shunt. The device has 100 internal posts, which enhance structural support while enabling aqueous humor to flow from the anterior entry point of the shunt in the anterior chamber to the posterior exit point of the shunt in the suprachoroidal space. The aqueous can flow freely around the posts and does not run through channels. Aqueous humor drains from the anterior side of the shunt placed in the anterior chamber, draining out the posterior side of the shunt in the suprachoroidal space. The free flow of aqueous around the internal posts in the SOLX Gold Shunt creates less flow resistance compared with prior generations of the device. Other improvements in this model include central fixation holes for easier implantation, increased tensile strength, and a preloaded inserter to improve handling (Fig. 34.2).

Rationale Behind the Procedure

Filtering procedures such as trabeculectomy and glaucoma drainage implants are currently the standard surgical approaches in the treatment of glaucoma. Both procedures are dependent on the formation of a filtering bleb, which has several well-known potential complications, including leakage with hypotony, subconjunctival fibrosis, bleb encapsulation, blebitis, and endophthalmitis.2 A bleb-less surgical approach that uses an alternative pathway for aqueous outflow would potentially avoid complications that can lead to poor outcomes.

A natural pressure gradient of 1 to 5 mm has been found to exist between the anterior chamber and the suprachoroidal space.3 Using a cynomolgus monkey model, Emi et al3 found that this pressure differential correspondingly increased with higher IOP levels when the anterior chamber and the suprachoroidal space was directly cannulated. It could then be inferred that a device connecting these two spaces could take advantage of this pressure gradient to directly lower the IOP, with subsequent flow of aqueous humor through the uveoscleral pathway. The SOLX Gold Shunt uses this approach to augment uveoscleral outflow from the anterior chamber to the suprachoroidal space, without bleb formation.

An observational case series of patients after Gold Shunt implantation by Mastropasqua et al4 confirmed the lack of formation of a filtering bleb in all patients after SOLX Gold Shunt model-GMS implantation with anterior segment optical coherence tomography (AS-OCT). In addition, using in vivo confocal microscopy, these investigators examined the conjunctiva of the patients, who were divided into two groups: successful Gold Shunt implantations (defined as a third reduction in preoperative IOP with or without antiglaucoma treatment) and failed implantations (defined as a less than a third reduction in preoperative IOP). There was a statistically significant difference in the number of both mean conjunctival microcysts density (cysts/mm2) and area (µm2) between the two groups, with the group of successful implantations exhibiting an approximately fivefold or sixfold increase in both numbers versus the failed implantation group. Epithelial microcysts have been previously identified as a marker for aqueous humor filtration through the conjunctiva in the bleb wall of successful trabeculectomies.5 The presence of microcysts in patients with successful Gold Shunt implantation could be interpreted as a sign of aqueous humor filtration across the sclera, providing evidence that this may be one of the possible outflow pathways used by the shunt.4

Patient Selection

Previous studies have examined the efficacy of the SOLX Gold Shunt in patients with refractory glaucoma, with uncontrolled IOPs on maximal medical therapy, or with a history of prior failed glaucoma surgery.69 Even in such a challenging patient population, the SOLX Gold Shunt appears to be efficacious and safe.68 Patients should have at least one quadrant of healthy scleral tissue for implantation, but otherwise it does not appear that a history of prior glaucoma surgery prevents performing subsequent SOLX Gold Shunt implantation. Likewise, SOLX Gold Shunt implantation itself does not seem to preclude further glaucoma surgery.9

Complication rates have been low after implantation of the SOLX Gold Shunt.69 This low rate of complications, along with the straightforward surgical procedure and the potential benefits of bleb-less surgery, suggest that there is a future role for the SOLX Gold Shunt in primary surgical treatment of glaucoma. In a clinical case series outside the United States of 103 patients with uncontrolled glaucoma (defined as baseline IOP > 21 mm Hg on maximum tolerated medications), the mean IOP reduction at 12 months was similar in subjects with a prior history of glaucoma surgery (n = 59) as compared with subjects with no prior history of glaucoma surgery (n = 44), with reduction rates of 31.6% and 34.5%, respectively (SOLX Inc., unpublished data). Successful treatment, defined as achieving an IOP ≤ 21 mm Hg, was achieved in 70.7% of patients with a prior history of glaucoma surgery, and in 93.9% of patients with no prior history of glaucoma surgery (SOLX Inc., unpublished data). For patients who have glaucoma not adequately controlled on maximal medical therapy, the SOLX Gold Shunt may be a useful primary surgical option in the future.

Surgical Technique

SOLX Gold Shunt Alone

Local anesthesia including retrobulbar, sub-Tenon, or peribulbar injection is usually sufficient. Either a corneal traction suture or a superior rectus bridle suture can be used for fixation.

The chosen quadrant for Gold Shunt placement should be in an area of healthy scleral tissue, with an open angle without any peripheral anterior synechiae.10 A fornix-based conjunctival flap is created, and episcleral vessels are cauterized. Either an anterior chamber maintainer or a cohesive viscoelastic should be placed via a paracentesis to maintain the anterior chamber. A 4-mm base by 3- to 4-mm-long scleral flap is created, with 80 to 90% scleral depth. A full-thickness scleral incision, 3.5 mm in length, is made 2 to 2.5 mm posterior to the scleral spur (Fig. 34.3). A second full-thickness scleral incision, again 3.5 mm in length, is made 1 mm posterior to the scleral spur leaving a 1-mm belt of scleral tissue between the two incisions (Fig. 34.4). A small amount of viscoelastic can be injected into both choroidal incisions. A 3.0-mm keratome is utilized to enter the supraciliary space through the anterior full-thickness incision (Fig. 34.5), gently advancing anteriorly to the entry point into the anterior chamber (Fig. 34.6). The incision is made into the anterior chamber with the keratome along the same plane as the supraciliary space (Fig. 34.7). The location and angulation of the anterior chamber entrance is an important step, with too anterior an entry leading to shunt-corneal touch, and too posterior an entry possibly leading to bleeding or iris touch.10 The Gold Shunt is placed underneath the scleral flap, using the included preloaded inserter, with the anterior end positioned into the anterior chamber using the positioning holes, and the posterior end placed over the 1-mm belt of sclera into the suprachoroidal space through the more posterior full-thickness incision (Fig. 34.8).

Oct 29, 2018 | Posted by in OPHTHALMOLOGY | Comments Off on Suprachoroidal Shunt: SOLX Gold Shunt
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