New Glaucoma Surgical Alternatives

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New Glaucoma Surgical Alternatives TAREK M SHAARAWY, MARILITA M MOSCHOS and MARK B SHERWOOD

Summary There has been, in recent years, a considerable surge in interest in glaucoma surgery; techniques, devices, (implants), and procedures to warrant earnest attention and research. Several new devices (and implants) are currently being evaluated in clinical trials, all of which aspire to the common goal of achieving acceptable efficacy and limiting the potential for major vision-threatening complications. Ongoing research is constantly working on ways to lower possible complications and adverse effects aiming to contribute to overall safety and efficacy of procedures. They all follow the common concept of delineating alternative pathways for aqueous drainage, either through Schlemm’s canal or the suprachoroidal space, aiming to bypass the area of abnormal resistance in the trabecular meshwork. Moreover, the interest in novel biomaterials, used in devices and implants, that confer desirable characteristics such as biostability and that invoke minimal inflammation and scar formation, to name a few, is deserved of continuous research. It remains to be seen whether they will provide adequate levels of IOP reduction, to the levels required by many patients with moderate-to-advanced disc damage from glaucoma, and whether they will be effective and complication-free in the long term. An essential point to consider is where to place these techniques in the surgical armamentarium for glaucoma. Some of these surgeries, because of their less-invasive nature and minimal, if any, damage to the conjunctiva and Tenon’s capsule, may fit into the spectrum of therapies that can be performed prior to trabeculectomy and should not significantly lessen the success of this type of surgery should it be later required. These devices and techniques have great theoretical advantages over external drainage techniques and the initial results with these new studies are encouraging. Clinical research in the next few years will aim to include multicentric studies with larger numbers of patients and longer follow-up so as to substantiate the long-term safety and efficacy of glaucoma surgical procedures.

paucity of published peer-reviewed studies to support an established place for these technologies in the routine practices of glaucoma surgeons and general ophthalmologists. In fact it is extremely hard at this point in time to make accurate evaluations of the utility of most of these technologies and devices. This chapter attempts to list what is commercially available, hitherto, to discuss the current literature and, perhaps, to speculate on future trends and possible positioning of these new methods in the expanding armamentarium of the ophthalmic surgeon.

Terminology There have been attempts to group most of these devices and technologies under headings like minimally invasive, minimally effective, and conjunctiva-sparing surgery.4–6 None of these terms are accurate for a number of reasons. Calling these methods and devices minimally invasive implies that they are less invasive than traditional and well-established glaucoma surgical methods like trabeculectomy, nonpenetrating glaucoma surgery, and tubes. These claims are not supported by evidence-based science, to date. In some of these novel methods the conjunctiva is opened, thus compromising at least one quadrant, which would possibly go against the ‘non-invasive’ terminology. Furthermore each new methodology being introduced since the 19th century has always carried with it the claim of being less invasive, and as such the terminology is abused and exhausted.7,8 Calling it minimally effective would first group the technologies in one single ‘effectiveness’ bracket which would not be unbiased towards or against certain technologies, and would imply that we have enough knowledge on effectiveness of such devices and methods, when we in fact do not possess such knowledge.

Classification Introduction It is safe to say that there has never been such interest in glaucoma surgery as that which we are witnessing today.1 Glaucoma surgery that has been relatively stagnant for many decades is now being rejuvenated with the introduction of new technologies.2 Each of these new surgical methods comes with the promise of improved surgical efficiency and safety compared to the eternal gold standard, trabeculectomy.3 Claim is one thing though, and scientific reality is another. Most of these technologies are still undergoing the early stages of clinical testing, with evident 1188

In our opinion, a safe and relatively accurate way of classifying such technologies would be to classify them according to their anatomic approach and thus we can list the technologies as: I Subconjuctival filtration strategy: a) Ab-externo approach Ex-PRESS Implant (see also Chapter 126) CO2 laser-assisted sclerectomy surgery (CLASS) InnFocus MicroShunt b) Ab-interno approach Aquesys Xen implant

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II Enhanced filtration into Schlemm’s canal strategy a) Ab-externo approach Canaloplasty (iScience Catheter) (see Chapter 127) Stegmann Canal Expander b) Ab-interno approach iStent High-frequency deep sclerotomy (HFDS) Ab-interno trabeculotomy (Trabectome or iScience Catheter) Hydrus implant III  Suprachoroidal filtration strategy a)  Ab-interno approach CyPass implant iStent supra implant b) Ab-Externo approach Starflo implant Gold Solx Implant

I  Subconjunctival   Filtration Strategy AB-EXTERNO APPROACH Ex-PRESS Implant (see also Chapter 126) The 2.64-mm stainless steel implant3,9–12 reduces pressure by diverting aqueous humor from the anterior chamber to the subscleral space after a dissection identical to a trabeculectomy with the exception of avoidance of surgical iridectomy (Video 128-1).13,14 Pressure release is initially the function of the implant’s length and inner diameter, until scarring starts in full force, and thus the pressure control is dependent on the same forces as after trabeculectomy. Multiple studies have found superiority for Ex-PRESS in the initial postoperative period where its standardized filter may be a preventing factor for early hypotony with all its associated complications.15,16 One other study also suggested that Ex-PRESS offers a faster visual rehabilitation to operated patients compared with trabeculectomy, which is a primordial factor that should always be taken into consideration17 (Fig. 128-1).

Figure 128-1  Implanted Ex-PRESS.

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On the other hand, there are no long-term results reporting on the corneal endothelial effects of Ex-PRESS compared to trabeculectomy, taking into consideration the fact that glaucoma drainage tube studies have shown a progressive long-term reduction of endothelial cells with time.18 One additional factor that should always be taken into account is the economical repercussions of the introduction of a new device into everyday surgical practice.9,19 Direct cost has a major impact, but is not the only factor that should be taken into consideration. Postoperative care in a procedure that has potential complications and the management of such complications should be factored in. Such studies need to be carried out on national levels as costs vary considerably among different countries and in many cases within the same country itself.

CO2 Laser-Assisted Sclerectomy Surgery (CLASS) When manually dissecting the deep corneo-scleral lamellae in deep sclerectomy there is always the potential for either perforation into the anterior chamber or insufficient tissue removal.20 This is highly dependent on the surgeon’s experience and skill.8 To overcome such challenges, different kinds of lasers (Fig. 128-2) were used to ablate the deep scleral tissue. Experimental and clinical studies using the excimer laser have also been reported with encouraging preliminary results.21 No comparative studies between laser-assisted deep sclerectomy and trabeculectomy are available as yet. Surgical Technique (see Chapter 97, Spotlight 4).  A partial-thickness (one-third to one-half) rectangular limbalbased 5 × 5 mm superior scleral flap is dissected at the limbus into the clear cornea (Fig. 128-3).

Figure 128-2  The Ioptima™ CO2 laser system. (Courtesy of Ioptima™.)

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A Figure 128-3  Partial-thickness rectangular limbal-based 5 × 5 mm superior scleral flap.

The desired scanning area and shape are set, the laser beam is focused, and the area to be treated is visually verified using a red laser aiming beam. The CO2 laser beam is then applied over an area including the Schlemm’s canal forming the scleral bed (Fig. 128-4). The residual charred tissue is wiped away with a sponge and ablation is continued until sufficient percolation is achieved, whereby the fluid absorbs laser’s energy and prevents further ablation (Fig. 128-5). The scleral flap is repositioned and secured with two interrupted 10/0 Nylon sutures and a high-molecularweight ophthalmic viscosurgical material (Healon 5®) is applied beneath the flap or an intrascleral implant (Aquaflow collagen implant from STAAR, Nidau, Switzerland, for example). The conjunctiva is adequately secured with 9/0 Vicryl continuous suture. The reported results are sufficiently promising to suggest that the CLASS is an easily learned and simple surgical procedure to perform, which appears to be relatively safe and effective in the short and intermediate term.22,23 Randomized controlled trials comparing CLASS to manual technique are needed to improve our knowledge and understanding on how to place this new technology among our existent options. The CO2 laser has certain properties that offer significant advantages to facilitate deep sclerectomy (Video 128-2). These include coagulation of bleeding vessels, photoablation of dry tissues, and absorption of the laser energy by percolating aqueous humor. As the emitted radiation is readily absorbed by the aqueous humor, the trabecular meshwork is potentially protected from the laser energy. Thus, perforation of the thin trabeculo-Descemet membrane during DS, which is the most frequent intraoperative complication of manual DS, is potentially minimized.

InnFocus MicroShunt The InnFocus MicroShunt consists of a flexible tube with planar fins, which are located approximately halfway down the length of the tube that prevent the device from migrating into the anterior chamber.24–26 The fins also act as a

B Figure 128-4  (A) Applied CO2 laser beam over scleral area including the Schlemm’s canal. (B) Starting percolation.

Figure 128-5  Residual charred tissue wiped away with a sponge.

‘stopper’ to minimize aqueous humor leakage around the tube and to reduce the likelihood of postoperative hypotony. The 70 µm diameter lumen of the device serves as a flow restrictor with the intention of avoiding hypotony yet dampening IOP spikes postoperatively (Fig. 128-6).

128  •  New Glaucoma Surgical Alternatives 1.1

0.35

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0.07

1 3.1

4.4

8.5 Figure 128-6  Schematic of the InnFocus MicroShunt.™ All units are in mm.

A highly biocompatible biomaterial, poly(styrene-blockisobutylene-block-styrene) or SIBS,24 is possibly a key feature of the InnFocus MicroShunt and is one of three elastomers which have been approved by the U.S. Food and Drug Administration (FDA) for use in the fabrication of medical devices intended for long-term implant applications. The SIBS material is biostable and its inert nature evokes minimal inflammation and scar formation. Initial studies of glaucoma drainage surgery in rabbit eyes compared the tissue response of tubes made from SIBS to silicone rubber tubes. Silicone rubber stimulates inflammation and promotes the development of a fibrotic capsule around the device that quickly becomes non-functional. In contrast, SIBS tubes demonstrated minimal encapsulation with continuous aqueous humor flow after one year. Implantation of the InnFocus MicroShunt™ is relatively simple and requires only the dissection of a subconjunctival/Tenon’s capsule flap and the development of a small scleral pocket to permit the passage of a needle tract into which the tube is inserted and the fins on the Micro­ Shunt are wedged. The procedure is performed ab externo and does not require the use of a gonioscope or viscoelastic fluid. Unlike trabeculectomy, neither sclerostomy nor iridectomy are necessary and the only scleral trauma is the needle tract (Fig. 128-7 and Video 128-3).

The surgeon dissects a fornix-based sub-conjunctival/sub-Tenon’s capsule pouch over 90°–120°. The posterior extent should be at least 8 mm posterior to the corneoscleral limbus

After 3 corneal shields soaked in MMC are placed under the flap

The surgeon marks a point on the scleral surface, 3 mm posterior to the surgical limbus. A half-thickness scleral pocket approximately 1 mm × 1 mm is dissected

The surgeon advances a 25 gauge needle through the scleral pocket into the anterior chamber

The surgeon advances the InnFocus MicroShunt through the needle tract with a forceps and wedges the fins of the shunt into the 1.0 mm wide scleral pocket.

After tucking in the distal end of the device under the sub-conjunctival sub’-Tenon’s capsule flap, the surgeon closes the wound with an interrupted 10-0 nylon suture.

AB-INTERNO APPROACH The Aquesys Xen Glaucoma Implant The XEN Implant is a hydrophilic tube composed of a porcine gelatin and cross-linked with glutaraldehyde (Fig. 128-8). It decreases intraocular pressure by creating an outflow pathway from the anterior chamber to the subconjunctival space through which the aqueous humor can flow. During the implantation procedure, the implant hydrates and swells in place to become a soft non-migrating drainage channel that is tissue-conforming (Figs 128-9, 128-10). Procedure.  The mechanism of action of the XEN Glaucoma Implant is fundamentally consistent with other full-thickness surgical treatments for glaucoma such as valved and non-valved tube shunts and full-thickness trabeculectomies, which bypass all potential outflow obstructions (Video 128-4). It maintains a micro-fistula between the anterior chamber and the subconjunctival space while

Figure 128-7  Implantation of the InnFocus MicroShunt.

the tissues surrounding the implant heal naturally. There is no need to perform an iridotomy and by introducing only a minimal amount of trauma, subsequent inflammation and fibrosis is potentially minimized and many of the complications associated with more invasive procedures such as trabeculectomy and tube shunt implantation can perhaps be avoided (Fig. 128-11).

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Figure 128-10  AS-OCT image of the Aquesys Xen implant in situ.

Figure 128-8  The XEN Implant is a hydrophilic tube composed of a porcine gelatin and cross-linked with glutaraldehyde.

Figure 128-11  The needle of the XEN Inserter is designed to be minimally traumatizing by utilizing a small 25 gauge needle.

Figure 128-9  Comparison between the size of the Xen implant and the Ahmed Glaucoma valve.

II  Enhanced Filtration into Schlemm’s Canal Strategy AB-EXTERNO APPROACH

the surgically created ostia of Schlemm’s canal, the microcatheter, as in canaloplasty, is inserted in the canal to dilate it circumferentially with highly viscous sodium hyaluronate. After completing dilation, the catheter is withdrawn and the SCE implant is placed inside both ostia of Schlemm’s canal. The rationale behind SCE is to maintain increased permeability of the TM, resulting in increased drainage of aqueous humor from the anterior chamber into SC. The superficial scleral flap is sutured watertight as in viscocanalostomy to avoid bleb formation and to force the aqueous humor leaving through the physiological drainage system. The device received the CE market approval in April 2013. Clinical trials are ongoing, but no results have been published to date (Personal Communication, M. Greishaber, University of Basel, Switzerland).

Canaloplasty (iScience Catheter) (see Chapter 127)

AB-INTERNO APPROACH

Stegmann Canal Expander The Stegmann Canal Expander (SCE)® (Ophthalmos GmbH, Switzerland) (Fig.128-12 A,B) is a polyimide implant designed to be inserted into Schlemm’s canal creating a permanent distension of the trabecular meshwork (Video 128-5). It has an outer diameter of 240 microns. Due to its fenestrations, SCE is patent to aqueous humor. SCE has been developed to make canaloplasty an easier and more reproducible procedure by replacing the suture stent. Stenting the canal with a suture would, theoretically at least, depend on the tension in the suture which is not easily evaluated or titrated, and has an inherent risk of cheese-wiring. After dilation of

Trabectome (Ab-Interno Trabeculotomy) Another relatively new surgical instrument is the trabectome.27 It has a handpiece with an aspiration port and a microelectrocautery ablation system28 controlled by a foot pedal. The backplate of the device is designed to protect the deep wall of Schlemm’s canal and the exiting vascular system. The intraocular portion is 19-gauge with its infusion sleeve and can be inserted through a 1.6 mm clear corneal keratome incision. It is advanced across the anterior chamber nasally under gonioscopic control. After insertion of the footplate of the trabectome into Schlemm’s canal, the foot switch activates the aspiration and electrosurgical elements and, by

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was IOP ≤18 mmHg and ≥20% reduction in IOP. Failure included increased glaucoma medications or subsequent surgery. Preoperative mean IOP was 21.6 ± 8.6 mmHg; the number of glaucoma medications was 3.1 ± 1.1. At 24 months postoperatively, mean IOP was reduced 29% to 15.3 ± 4.6 mmHg (p < 0.001) and the number of glaucoma medications was reduced 38% to 1.9 ± 1.3 (p < 0.001) with a success rate of 62% using the first criterion and 22% using the second criterion. Failure risk factors included primary OAG and past argon laser trabeculoplasty. Of the cases, 66 (26.8%) required subsequent surgery on an average of 10 months (2 days to 3.2 years) after ab-interno trabeculotomy. The authors concluded that for criteria involving IOP ≤18 mmHg, the 24-month survival of ab-interno trabeculotomy is low. They recommended that this surgery should be considered only for patients requiring a target IOP of 21 mmHg or above. Ab-interno trabeculectomy is possibly the procedure, among the new alternatives, with the most extensive information available in the literature (see Chapter 125),5,6,27–41 and as such its limitations and advantages are relatively well-understood by now (Video 128-6).

A

360° Ab-interno Trabeculotomy with the iScience Canula The iScience canula described in a prior chapter for ab-externo cannulization and identification of Schlemm’s canal has also been recently used ab-interno.42 B Figure 128-12  (A & B) The SCE. (Courtesy of M Greishaber, MD.)

gently advancing the tip both clockwise and counterclockwise, ablates a strip of trabecular meshwork, opening a 60–120° (2–4 clock hours) section. Transient bleeding into the anterior chamber occurs from the cut meshwork and is washed out through the temporal incision. An initial report29 described 37 Mexican Hispanic and Caucasian patients with uncontrolled open-angle glaucoma and noted a mean IOP of 17.4 mmHg at 6 months (n = 25) and 16.3 mmHg at 1 year (n = 15), on or off medication. Complications included some degree of blood reflux in all eyes, causing hyphemas, which resolved within a week without long-term visual consequences in the majority of patients. Corneal Descemet’s injury, mainly transient, occurred in three eyes and nine developed peripheral anterior synechiae. Minckler and colleagues27 later reported on the initial 101 eyes that underwent this surgery with up to 30 months follow-up for 11 patients. At 3 months (n = 51) the mean IOP was 17.6 mmHg (40% drop in IOP), at 12 months (n = 37) mean IOP was16.4 mmHg (44% IOP drop), at 24 months (n = 18) 15.2 mmHg (44% IOP drop), and at 30 months (n = 11) 16.3 mmHg. Sixteen eyes were classified as failures (16%), with nine undergoing trabeculectomy surgery and a further seven having an IOP >21 mmHg. A recent study reported the results from 246 patients undergoing ab-interno trabeculotomy.30 Kaplan–Meier analysis was performed using two different criteria. The first criterion was a postoperative IOP ≤21 mmHg or ≥20% reduction from preoperative IOP and the second criterion

Surgical Technique: (see Video).  A 23-gauge needle tract is made in the cornea for passage of the cannula and a second small 1–2 mm paracentesis corneal tract made for manipulation of the cannula by means of a 25-gauge vitrectomy forcep. After viscoelastic has been placed into the anterior chamber an NVR blade is passed across the chamber and a small scratch incision made in the trabecular meshwork to enter Schlemm’s canal. The cannula is internally inserted into Schlemm’s and under gonioscopic control is passed 360° around, with the flashing red HeNe light denoting its circumferential progress. After reaching the start point, by pulling on the two ends of the cannula the internal wall of Schlemm’s is broken down thus allowing direct aqueous access to the aqueous veins 360°. Later postoperative fibrotic scarring can be a problem with some patients, but initial results have been promising and the conjunctiva is spared for possible further procedures should they be necessary.

iStent The Glaukos iStent43,44 (Glaukos Corp., Laguna Hills, CA) is a titanium, one-piece, ‘L’-shaped device which, via a clear corneal incision, is internally placed into Schlemm’s canal, usually in the nasal quadrant (Video 128-7). The canal portion is half-pipe-shaped, 1 mm long, with a 180 µm outside diameter, and designed to fit within the lumen of the canal, with a curved convex side that lies against the inner wall of the canal. It has a tubular, small ‘snorkel,’ about 0.5 mm long, which sits in the peripheral anterior chamber and acts as a conduit for aqueous to bypass the inner wall of Schlemm’s canal, and the juxtacanalicular trabeculum, thus increasing outflow facility. The anterior chamber is filled with a viscoelastic agent, and under gonioscopic control an applicator with the device grasped in its

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jaws traverses the chamber to engage the trabecular meshwork opposite the entry site with its pointed leading tip. In vitro studies by Bahler et al.45 using human cadaver anterior segments in perfusion culture have suggested that, although initially placing two or more stents gave statistically the same IOP level as placing a single stent of around 12 mmHg, sequentially placing a second or third iStent in another part of Schlemm’s canal may reduce final IOP further. In a recent randomized controlled study46 Craven and co-workers reported on the long-term safety and efficacy of a single trabecular micro-bypass stent with concomitant cataract surgery versus cataract surgery alone for mild to moderate open-angle glaucoma. Eyes with mild to moderate glaucoma with an unmedicated IOP between 22 mmHg and 36 mmHg were randomly assigned to have cataract surgery with iStent trabecular micro-bypass stent implantation (stent group) or cataract surgery alone (control group). Patients were followed for 24 months postoperatively. They reported a low incidence of adverse events in both groups through 24 months of follow-up. At 24 months, the proportion of patients with an IOP of 21 mmHg or lower without ocular hypotensive medications was significantly higher in the stent group than in the control group (p = 0.036). Overall, the mean IOP was stable between 12 months and 24 months (17.0 mmHg ± 2.8 [SD] and 17.1 ± 2.9 mmHg, respectively) in the stent group but increased a little (from 17.0 ± 3.1 mm Hg to 17.8 ± 3.3 mmHg, respectively) in the control group. Ocular hypotensive medication was statistically significantly lower in the stent group at 12 months; it was also lower at 24 months, although the difference was no longer statistically significant. A second-generation iStent (GTS-400) (Fig. 128-13 A,B) has recently been reported;47 in a non-comparative case series 20 patients with co-existing open-angle glaucoma or ocular hypertension, and cataract, were enrolled. Mean medicated baseline IOP was 19.95 ± 3.71 mmHg and 26 ± 3.11 mmHg without medication. Mean final IOP was 16.75 ± 2.24, determining a final IOP decrease of 35.68% (9.42 ± 3 mm Hg; p < 0.001), from baseline washout IOP. Mean number of medications fell from 1.3 ± 0.66 to 0.3 ± 0.57 (p < 0.001). A total of 75% of patients were off medications at one year.

High-Frequency Deep Sclerotomy (HFDS) HFDS is an interesting surgical approach for lowering IOP in patients with open-angle glaucoma. It channels an outflow of fluid through the trabecular meshwork and into Schlemm’s canal (Fig. 128-14). Surgical Technique.  After creating two 1.2 mm clear corneal incisions in an arc of approximately 120 degrees, the surgeon fills the chamber with a cohesive ophthalmic viscoelastic. Using a new diathermic probe design (Abee Glaucoma Tip; Oertli Instrumente AG, Berneck, Switzerland) the procedure can be performed from a temporal, superotemporal or superonasal position. The tip has the following dimensions; 1 mm long, 0.3 mm high and 0.6 mm wide. The process is repeated until 4–6 sclerotomies are placed. HFDS is an ab-interno approach (Video 128-8), thus it has no known negative impact if a second glaucoma surgery is needed, as it is performed nasally and/or inferiorly, allowing the surgeon to intervene with other glaucoma surgeries

A

B

C Figure 128-13  A, First generation. (B & C) A second-generation iStent (GTS-400).

superiorly and with an ab-externo approach. HFDS is reported to have low complication rates and the learning curve for the surgeon is very brief (Fig. 128-15 A,B). Results.  Pajic and co-workers48 performed HFDS in 58 eyes of 58 consecutive patients, of which 53 were diagnosed with open-angle and five with juvenile glaucoma. The average baseline intraocular pressure (IOP) was 25.6 ± 2.3 mmHg (range: 18–48 mmHg) for the open-angle glaucoma group and 39.6 ± 2.3 mmHg (range: 34–46 mmHg) for the juvenile glaucoma group. All patients had a minimum follow-up of 72 months. The mean IOP for the stated period was 14.7 ±  1.8 mmHg for the open-angle glaucoma group and 13.2 ± 1.3 mmHg for the juvenile group. The IOP after surgery was statistically significantly lower than the baseline IOP at all measured intervals (p < 0.001). After 72 months only 11 eyes accounted for a 20.8% continuous antiglaucoma therapy. No serious complications were reported.

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Hydrus Implant This is a scaffold-like implant49 inserted ab-interno into SC to help in keeping the canal open, thus enhancing the physiological conventional outflow of aqueous. It is flexible in nature and is made of biocompatible nickel titanium alloy (Video 128-9). It is open posteriorly along its 8 mm length, and has three open windows along its anterior surface. It is supposed to support the SC along 3 clock-hours length targeting multiple collector channels (Fig. 128-16 A–E).

III  Suprachoroidal Filtration AB-INTERNO APPROACH Figure 128-14  High-frequency deep sclerotomy (HFDS).

CyPass Implant CyPass is a miniature tube of 6.35-mm length with a 300µm lumen made of biocompatible polyimide. It is designed to shunt aqueous outflow towards the suprachoroidal space (Video 128-10). The Procedure.  Through a 1.5-mm incision, an ab-interno approach is planned under the guidance of a direct gonioscopy lens. The anterior chamber is filled with viscolelastic material and the injector, with the uploaded tube, approaches the angle structure and targets the area at the deepest end of the angle structures. As the device is inserted in between the spongy soft choroid and the relatively rigid sclera, the tube creates a plane of separation and the potential for misdirection is minimized by the significant difference of rigidity between the two adjacent structures (Figs 128-17, 128-18A,B).

A

iStent Supra Implant Very little information is available regarding the clinical performance of the third generation of iStent. Despite maintaining the ab-interno approach, the iStent supra implant aims at targeting the suprachroidal space, which is a deviation from previous strategy of enhancing the conventional pathway through SC. To date there are no publications that offer further insight on the research carried out on this implant (Fig. 128-19).

AB-EXTERNO IMPLANT Starflo Implant Designed for suprachoroidal placement to augment natural uveoscleral outflow, the implant is made from soft, spongy, so-called ‘tissue-friendly’ non-degradable STAR® Biomaterial (Fig. 128-20).51,52 The implant dimensions are 11 mm length with a head (5 mm wide), neck (3 mm wide), and body (6 mm wide). Edges of the implant are rounded.

B Figure 128-15  (A & B) High-frequency deep sclerotomy – surgical technique.

The Procedure.  Under local or topical anesthesia, a fornixbased conjunctival flap is created. The anterior chamber is maintained during surgery with the help of viscoelastics or with an anterior chamber maintainer. A superficial half-thickness scleral flap, 8 mm width × 3 mm length, is then created. The sclera is incised

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B

A

C

D E Figure 128-16  (A–E) In an ocular biocompatibility study, Grierson et al.50 implanted the Hydrus device in the eyes of eight rabbits and the Schlemm’s canal of two monkeys, showing minimal inflammatory response compared to sham eyes. (D, Courtesy of Ivantis.)

Figure 128-17  CyPass – a miniature tube of 6.35-mm length with a 300-µm lumen made of biocompatible polyimide.

until the choroid is identified, leaving a scleral bridge of 1–2 mm (Fig. 128-21). A central 3 mm width incision, through the trabecular meshwork, is performed reaching the anterior chamber. A blunt spatula is used to separate sclera from choroid creating a pocket for implant insertion. The implant body is gently introduced through the 7–8 mm width scleral incision and glided posteriorly over the choroid until two-thirds of the implant has entered the suprachoroidal space. One corner of the implant head is inserted into the anterior chamber through the 3 mm incision, followed by the other corner. When correctly placed the device neck should be centered in the 3-mm incision and should lay flat on the sclera without folds. The superficial scleral flap is sutured tightly to avoid bleb formation, and finally the conjunctiva is closed. The idea of the ab-externo implant is not new. The same concept was explored in the past in the Gold micro-shunt.6,53,54 In this new trial for an ab-externo enhancement of suprachoroidal flow, the interesting factor might be the new non-degradable biomaterial and its potential benefits

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50 µm A

A

Figure 128-18  (A & B) CyPass implant – Ab interno approach.

B Figure 128-20  (A & B) Starflo implant.

Figure 128-19  iStent supra implant.

regarding tissue scarring and modulation of inflammation, though this has not yet been validated in clinical studies.

Gold Micro-Shunt The Gold Micro-Shunt53–57 (GMS) is a flat 24-karat gold plate that is approximately 5.2 mm long and 3.2 mm wide with a thickness of 44 µm. The GMS is made of 99.95% pure gold, a biocompatible material that is hoped to minimize tissue ingrowth or protein adherence that could cause blockage of aqueous flow. It is implanted into the suprachoroidal space with a special insertion tool through either a single 3–3.5mm-wide subscleral or clear cornea incision. Newer models

have been developed with larger microtubular channel diameters (XGS-5 and XGS-10 [GMS+]) (Fig. 128-22). There is a difference in pressure between the anterior chamber and the suprachoroidal space, and the GMS uses the eye’s natural pressure differential to reduce IOP without a bleb. The shunt contains a series of microtubular channels that connect the anterior chamber with the suprachoroidal space. The shunt is also novel because it potentially allows the surgeon to control the amount of fluid that flows from one area to another using a laser. Ten of the 20 channels on the GMS are open upon implantation. It is suggested that if the IOP is too high postoperatively, some of the originally sealed channels can be opened using the DeepLight® 790 titanium–sapphire laser. The idea is that even years after surgery, rather than adding extra drops, the surgeon will be

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A Figure 128-21  Starflo implant – procedure. Backing Gen II (2007)

GMS + (2011)

AC

Coupling water

HIFU device

3.2 mm Coupling cone 2.2 mm 1.9 mm 5.5 mm

Focal spot

Suction ring

1.9 mm 5.5 mm

2.1 mm 3.2 mm B

Figure 128-22  Gold Micro-Shunt.

able to open up these additional channels and achieve an incremental reduction in IOP. Recently a retrospective study reported the results of 31 severe glaucoma cases implanted with GMS+. The main outcome measures were surgical failure or success, based on the intraocular pressure and adverse effects. Clinical examination data are reported up to 4 years postoperatively. Thirty eyes (97%) met one of the criteria for failure as determined by the authors. Within a mean of 7.3 ± 7.7 months, another surgery was performed because of elevated IOP in 24 of 31 eyes (77%) and because of adverse effects in two (6%). Four eyes had an IOP reduction of less than 20% with comparable medication. Six GMS were explanted, because of IOP elevation. They reported two cases of rubeosis iridis, and two cases of low-grade inflammation. They concluded that GMS implantation is not an effective method to control IOP in patients with glaucoma. The reason for the found signs of chronic low-grade inflammation or rubeosis iridis in four eyes (13%) was not provided.58 A multicenter study is underway comparing the Gold Micro-Shunt with the Ahmed valve.

C Figure 128-23  HIFU procedure.

Miniaturized High-Intensity Focused Ultrasound   Device (HIFU) Ultrasonic ablation of the ciliary body for treating glaucoma was extensively studied in the 1980s and 1990s. HIFU is an

128  •  New Glaucoma Surgical Alternatives

effective method with favorable results in terms of IOP reduction. Recently59 a miniaturized circular HIFU device was used to produce cyclocoagulation and a circular instrument with six miniaturized high-frequency transducers was developed. The circular geometry of the device, located directly in contact with the eye, allows for constant and reproducible positioning in most eyes and reduces the procedure time and the risk for misplacement. High-frequency miniaturized transducers enable the creation of smaller focal zones that better target the ciliary body. The higher operating frequency of such transducers also allows for a steeper transition between the focal zone and the untreated area, thus reducing the risk for heating the neighboring healthy tissue. Ultrasonic circular cyclocoagulation using HIFU seems to be relatively safe and potentially effective in reducing IOP in patients with refractory glaucoma.60 No major

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complications during or after the procedure have been observed in early studies and a mean IOP reduction of 35.7% is achieved three months after treatment.60,61 The mechanism of IOP reduction after HIFU treatment remains to be clarified. It is assumed that the main mechanism for IOP reduction was a decrease of aqueous production by the treated ciliary body. Because the coupling cone was placed in direct contact with the eye and was fixed by means of a vacuum suction ring, it is assumed that the procedure effectively targeted the ciliary body and no other surrounding structures. The ultrasonic coagulation of the ciliary body using high-intensity focused ultrasound delivered by miniaturized high-frequency transducers seems to be an effective method of reducing IOP and theoretically may be safer than other cyclodestructive procedures (Fig. 128-23).

Spotlight 1  Combined Trabecular Micro-Bypass Stent Implantation and Phacoemulsification Julián García-Feijoó

There is an increasing interest in micro-invasive glaucoma surgery (MIGS) procedures.1 The Glaukos iStent™ (Glaukos Corporation, Laguna Hills, California) is designed to connect the anterior chamber to Schlemm’s canal, bypassing the trabecular meshwork. Once phacoemulsification has been completed, the anterior chamber is refilled with a cohesive viscoelastic, the surgical microscope and the patient’s head are repositioned and a goniolens is placed on the cornea. The angle is easier to visualize and the surgery is easier to perform in pseudophakic eyes. The inserter is introduced into the anterior chamber through a temporal approach and the stent is placed into Schlemm’s canal in a nasal position. It should be parallel to the iris root with the rails located on the back wall of Schlemm’s canal (Fig. 1). If two implants are used, one is placed inferonasally and the other superonasally.

Figure 1  One week after surgery. Stent in the Schlemm’s canal, parallel to the iris plane and with the snorkel away from the iris. Note the blood in the Schlemm’s canal.

Candidates for combined surgery using the iStent are patients with a cataract and mild or moderate primary open-angle glaucoma (POAG) with an uncompromised Schlemm’s canal or outflow collector channels. Glaukos iStent has just received FDA approval for the treatment of glaucoma. In the author’s experience mean IOP significantly decreased 16.3% after 53 months of follow-up.2 A recent randomized clinical trial3 comparing a trabecular microbypass stent combined with phacoemulsification to phacoemulsification alone with one-year follow-up showed a significantly higher percentage of patients with unmedicated IOP ≤21 mmHg, and a comparable safety profile. Two-year safety and efficacy data from the same study has just been published, showing similar results.4 Initial results are published regarding a second-generation micro-bypass stent (iStent inject, Glaukos Corporation, Laguna Hills, CA, USA) showing a decrease in mean postoperative IOP.1 This surgical technique is a safe and effective treatment in the short- and mid-term with excellent biocompatibility. It offers a more rapid and less invasive approach compared with other combined procedures and the conjunctiva is preserved for future surgeries. References 1. Saheb H, Ahmed II. Micro-invasive glaucoma surgery: current perspectives and future directions. Curr Opin Ophthalmol 2012;23:96–104. 2. Arriola-Villalobos P, Martínez-de-la-Casa JM, Díaz-Valle D, et al. Combined iStent trabecular micro-bypass stent implantation and phacoemulsification for coexistent open-angle glaucoma and cataract: a long-term study. Br J Ophthalmol 2012;96:645–9. 3. Samuelson TW, Katz LJ, Wells JM, et al. Group. Randomized evaluation of the trabecular micro-bypass stent with phacoemulsification in patients with glaucoma and cataract. Ophthalmology 2011;118:459–67. 4. Craven ER, Katz LJ, Wells JM, et al. iStent Study Group. Cataract surgery with trabecular micro-bypass stent implantation in patients with mild-to-moderate openangle glaucoma and cataract: Two-year follow-up. J Cataract Refract Surg 2012;38:1339–45.

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SECTION 18  •  Devices in Development and New Procedures

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57. Oatts JT, Zhang Z, Tseng H, et al. In vitro and in vivo comparison of two suprachoroidal shunts. Invest Ophthalmol Vis Sci 2013; 54(8):5416–23. 58. Hueber A, Roters S, Jordan JF, et al. Retrospective analysis of the success and safety of Gold Micro Shunt Implantation in glaucoma. BMC Ophthalmol 2013;13(1):35. 59. Aptel F, Charrel T, Palazzi X, et al. Histologic effects of a new device for high-intensity focused ultrasound cyclocoagulation. Invest Ophthalmol Vis Sci 2010;51(10):5092–8. 60. Charrel T, Aptel F, Birer A, et al. Development of a miniaturized HIFU device for glaucoma treatment with conformal coagulation of the ciliary bodies. Ultrasound Med Biol 2011;37(5):742–54. 61. Aptel F, Lafon C. Therapeutic applications of ultrasound in ophthalmology. Int J Hyperthermia 2012;28(4):405–18.