Technique

As in standard trabeculectomy, a conjunctival peritomy is followed by a scleral flap dissected forward so as to provide a clear view of the scleral spur. The dimensions of this flap should be slightly larger than that in standard trabeculectomy so as to cover fully the footplate of the device. Once the glistening white fibers of the scleral spur are visible, the anterior chamber should be pressurized with an ophthalmic viscosurgical device (OVD) via a paracentesis incision, or a cataract incision, if part of a combined procedure. An entry is made into the anterior chamber at the level of the scleral spur using either a sapphire blade, manufactured by Optonol, or a 25-gauge hypodermic needle (Fig. 41.1). The angle of entry into the anterior chamber must be parallel to the iris plane. An entry angled perpendicular to the spur will result in an excessively posterior shunt impinging on iris, perhaps with tip occlusion, corectopia, and photophobia. An entry angled excessively anteriorly will rest the tip near the corneal endothelium. The ideal position for the shunt is to be parallel to the iris surface (Fig. 41.2). Once the shunt is in a satisfactory position, the OVD may be aspirated with a dry technique and the anterior chamber pressurized with balanced saline solution (BSS). The scleral flap is sutured at its corners similar to a standard trabeculectomy; flow can be assessed with a surgical sponge. With suture tension adjusted to attain satisfactory flow, the conjunctiva is closed in a watertight fashion.

Fig. 41.1 A sapphire blade is shown about to enter the anterior chamber at the level of the scleral spur.

Fig. 41.2 An intraoperative gonioscopic view after insertion of the Ex-PRESS shunt showing the shunt shaft parallel to the iris plane.

Discussion

Several studies have demonstrated effective IOP lowering and decreased medication usage with the Ex-PRESS shunt^8,9 and more recently, prospective and retrospective studies have found the device to be comparable with conventional trabeculectomy^10,11. In traditional trabeculectomy surgery, aqueous egress from the anterior chamber is regulated by the size of the ostium and of the scleral flap as well as suture tension. Although the Ex-PRESS shunt depends also on subconjunctival flow to lower IOP, it provides a consistent and reproducible ostium size, which may be challenging with a standard trabeculectomy punch. As well, without a large ostium, the Ex-PRESS shunt is inserted through a small entry into the anterior chamber improving anterior chamber stability during entry, as well as obviating the need for a surgical iridectomy. While in trabeculectomy, a surgical iridectomy may also be avoided, the creation of the large punch opening, combined with a shallowing of the anterior chamber, commonly results in iris presenting at the trabeculectomy site requiring a surgical iridectomy. This is notable in patients with narrow angles or shallow anterior chambers where enhanced anterior chamber stability may be more important. In our experience the Ex-PRESS shunt is well suited for narrow angle patients who require filtration surgery.

As the main control of aqueous outflow in filtration surgery is the suture tension and quality of the scleral flap, the benefit of the fixed lumen size may be minimal. Similar in many ways to conventional trabeculectomy, the Ex-PRESS shunt offers benefits over standard penetrating surgery and allows the surgeon to minimize fluctuations in anterior chamber dynamics, as well as to eliminate the need for a surgical iridectomy.

Technique

A conjunctival peritomy begins the procedure similar to trabeculectomy. This is followed by fashioning a parabolic scleral flap, the shape chosen to enhance the ability to achieve watertight closure. This flap is dissected forwards into the peripheral clear cornea at approximately scleral thickness. A deep scleral flap is created, approximately 1 mm within the borders of the superficial flap and the depth such that approximately 100 µm of sclera remain in the bed of the dissection. As this dissection is carried forward, the glistening white fibers of the scleral spur should appear in the bed of the dissection and, immediately anterior to this, the canal of Schlemm is seen to split open. The dissection must be carried forward at a consistent depth: dissecting excessively deeply will penetrate the eye; conversely superficial dissection will pass over the canal without accessing it.

The dissection is continued forward into peripheral clear cornea for approximately 2 mm exposing the trabeculo-Descemet window (TDW) (Fig. 41.3). Extreme care must be taken with the TDW as it easily ruptures, even with a wet surgical sponge. Once the TDW has been exposed, the deep flap is excised. The microcatheter is introduced into one of the cut ends of the canal and under fiberoptic illumination guidance is advanced carefully around the entire circumference until the tip emerges from the opposite cut end (Fig. 41.4). Once this has been achieved a suture, typically 10-0 Prolene, which the authors prefer, is tied to the distal end with two loose ends tied to the loop. The microcatheter is retracted 360° in the opposite direction, while an assistant injects a metered dose of OVD into the canal. Once fully retracted, the suture is cut from the microcatheter and the result is two loose suture ends emerging from each cut end of Schlemm’s canal. These ends are carefully corresponded and tied down in a slipknot fashion over the TDW. As the suture is tensioned, an inward dimpling of the TDW should be visualized, occasionally accompanied by an increase in aqueous humor percolation seen to emerge through the TDW (Fig. 41.5). The second suture is then tied down in a similar fashion. The superficial scleral flap is replaced and sutured down in a watertight fashion with typically five interrupted sutures, and finally followed by watertight conjunctival closure.

Fig. 41.3 After dissection of the superficial and deep scleral flaps, the trabeculo-Descemet window (TDW) is exposed.

Fig. 41.4 The iScience microcatheter device is seen having fully cannulated Schlemm’s canal.

Fig. 41.5 Two suture knots seen indenting the TDW after retraction of the catheter.

Discussion

The goal of canaloplasty is to restore or augment the outflow of aqueous via the conventional pathway by suture mediated distension of Schlemm’s canal. The tensioned suture attempts to reverse the process of canal collapse in glaucomatous eyes and thus to lower IOP. In the longest follow-up studies to date, at 2 years postoperatively, the mean IOP in patients undergoing canaloplasty alone was reduced from 23.3 mmHg to 16.3 mmHg and the mean number of medications used was reduced from 2.0 to 0.6. In patients undergoing combined cataract surgery with canaloplasty, the mean IOP was reduced from 23.1 mmHg to 13.4 mmHg and medication numbers decreased from 1.7 to 0.2¹². Suture tension has been shown in studies to be critical to obtain IOP lowering, with greater distension correlating with greater lowering of IOP¹³. Aqueous egress through the TDW and into the scleral lake, the potential space underneath the superficial scleral flap, also occurs and is potentially an important mechanism of IOP reduction. From the scleral lake, aqueous may exit into Schlemm’s canal, into the suprachoroidal space, directly into scleral, episcleral, and choroidal vascular channels, and/or emerge subconjunctivally to form a bleb, despite watertight closure. In some cases, fibrosis of the scleral lake, or at the level of the TDW, increases IOP necessitating an yttrium–aluminum–garnet (YAG) laser goniopuncture to restore aqueous flow into this space. To date, clinical studies available show excellent efficacy in IOP lowering with a low complication profile, reduced medication usage, and minimal postoperative management. However, the primary challenges are the technical difficulties involved in performing canaloplasty. This procedure is covered in more detail elsewhere in this book.

Technique

Although the iStent may be performed as a stand-alone procedure, it is easily combined with cataract surgery, its implantation not requiring any additional incisions. After the angle has been inflated generously with OVD, the patient’s head, as well as the operating microscope, should be rotated approximately 30–45° away from the surgeon for optimal visualization and approach to the angle. A gonioprism is placed on the eye to see the angle. The device, preloaded on a squeeze handle injector, is introduced into the eye through a corneal incision with the angle of approach to the meshwork approximately 15°.

Once visualization is satisfactory, the tip of the device engages the trabecular meshwork and is advanced tangentially to the elbow of the device, being careful not to advance excessively, as this could result in tearing of the trabecular meshwork and inner wall of the canal (Fig. 41.7). Once a satisfactory position is attained, the index finger of the surgeon’s implantation hand is depressed, releasing the snorkel and device from the four-pronged grasping mechanism. A small amount of blood reflux may be encountered and should be expected, confirming the placement of the device in the canal. OVD can be used to displace the blood, clearing the view of the snorkel and device, to confirm its acceptable position (Fig. 41.8). Occasionally, the snorkel requires a gentle tap from the OVD cannula to ensure that it is fully seated in the canal. Irrigation and aspiration are then used to remove OVD from the eye, and the incisions are checked to be watertight.

Fig. 41.7 The trabecular microbypass stent approaching the angle under direct visualization with a Swan–Jacob gonioprism.

Fig. 41.8 Gonioscopic intraoperative confirmation of proper trabecular microbypass stent placement.

Discussion

The ab interno approach of the iStent allows surgeons to bypass the JTM resistance point facilitating access of aqueous to Schlemm’s canal, thereby augmenting outflow via the conventional pathway. In a mathematical model of trabecular meshwork bypass, unidirectional and bidirectional flow would improve aqueous outflow facility by 13% and 26% respectively; also, the higher the initial IOP, the greater is the resultant reduction^14,15. However, this relationship has been less clear in in vitro studies. While the insertion of a single stent resulted in an IOP reduction from 21.4 mmHg to 12.4 mmHg, insertion of additional stents did not result in as clear a benefit in IOP reduction¹⁶. Despite the theoretical mathematical models of JTM bypass via the iStent, the clinical efficacy in IOP lowering depends on circumferential flow in Schlemm’s canal, which may not be present in glaucomatous eyes with collapse of the canal. This raises further questions as to whether multiple stents provide an increased likelihood of circumferential flow, as well as whether strategic placement of the stents adjacent to or overlying collector channels increases IOP lowering. These issues remain insufficiently studied and require further investigation. Despite these unanswered questions, two studies have been published showing effective IOP lowering as well as decrease in topical medication usage in patients undergoing trabecular microbypass stent implantation combined with cataract surgery. One study reported a mean reduction of IOP from 21.7 mmHg to 17.4 mmHg at 12 months follow-up and a decrease in number of medications from 1.6 to 0.4¹⁷. The other demonstrated IOP reduction from 19.6 mmHg to 15.8 mmHg and a reduction in medication numbers from 2.7 to 1.7 at 12 months follow-up¹⁸.

An ab interno approach to augment conventional outflow pathways has advantages over ab externo approaches. First, the stents may be placed utilizing the previously formed small incisions made for cataract surgery if the patient is undergoing combined cataract extraction and stent placement. And second, the conjunctiva is left undisturbed should conventional filtration surgery be required later. Further, avoidance of a subconjunctival bleb decreases the likelihood of vision-threatening complications such as persistent hypotony and bleb-related issues. Other advantages of this approach include protection against hypotony due to downstream episcleral venous resistance as well as the relative ease of placement of the device. While postoperative management and care are minimal, some cases of iris or fibrin occlusion of the stent snorkel have been observed. This can be managed with laser treatment to the iris, or slit-lamp needle sweeping of the iris to reopen the stent. Because of this potential complication, a narrow anterior chamber angle or a shallow chamber is a relative contraindication to the iStent. Other potential complications include stent migration, dislocation, transient postoperative hyphema, and inadequate IOP control requiring traditional filtration surgery or a GDD.

Technique

In a similar fashion to the trabecular microbypass stent, the Trabectome may be performed as a stand-alone procedure or combined with cataract surgery through the same incisions. While the technique has been described with performance of the trabecular ablation before cataract surgery if being performed in combination, we prefer to perform the cataract surgery first and then the ablation. While both techniques have their advantages, removing the cataract first increases the depth of the anterior chamber in most cases, and removes the risk of traumatizing the crystalline lens. Constricting the pupil with miotics to perform the trabecular ablation creates the inconvenience of having to re-dilate the pupil for cataract surgery. Finally, after Trabectome treatment, blood reflux into the anterior chamber is commonly seen, which may impair the surgeon’s view during cataract surgery.

After the cataract has been removed, the patient’s head is turned approximately 15–30° and the operating microscope tilted away from the surgeon. A gonioprism, such as the Swan–Jacob gonioprism, permits a direct view of the anterior chamber angle, which is inflated with a heavy OVD. The Trabectome hand piece is inserted into the eye and, under direct visualization, the pointed tip is used to incise the trabecular meshwork until the footplate of the device rests in the canal. The foot pedal is depressed to initiate ablation and the hand piece advanced in the direction that the tip is pointing until further progress is prevented by either the angle of approach or visualization (Fig. 41.10). The hand piece tip may be turned to face the opposite direction and a similar ablation performed until no further progress can be made. Blood reflux is common, but is usually managed adequately by irrigation and aspiration provided by the hand piece as well as the heavy OVD, which tamponades the blood. Once the ablation is completed, the OVD is removed and the wounds checked to be watertight. A clear corneal suture and intracameral air at the conclusion of surgery are associated with smaller amounts of postoperative hyphema¹⁹.

Fig. 41.10 The Trabectome device during the process of trabecular electrocautery ablation. Note the blood reflux into the anterior chamber to the right of the image in the area which has just been cauterized.

Discussion

Similar to the trabecular microbypass stent, the Trabectome creates a direct communication for aqueous between the anterior chamber and the Schlemm’s canal collector channels through the length of the ablated arc. This bypasses the JTM resistance point. Several studies have been published, both as a stand-alone procedure, as well as combined with phacoemulsification. In the stand-alone group, the mean IOP fell from 25.7 mmHg to 16.6 mmHg at 24 months of follow-up with the mean medication numbers decreasing from 2.93 to 1.24. However, there was a significant drop-off in the number of patients who reached 24 months follow-up (from n = 738 to n = 46). In patients undergoing combined surgery, the mean IOP decreased from 20.0 to 15.5 mmHg with the mean medication usage decreasing from 2.65 to 1.44; again at the 24 month follow-up there was a significant drop in numbers (n = 366 to n = 45)²⁰. The most common complications reported with the Trabectome include transient postoperative hyphema, peripheral anterior or goniosynechiae, transient corneal injury, Descemet’s detachment and hemorrhage, persistent Descemet’s injury, inadvertent iris injury, and transient early hypotony^19,20. Patients with narrow angle configurations may not be suitable for the Trabectome treatment.

The advantages of the Trabectome are similar to those for the trabecular microbypass stent, including avoidance of a bleb and its associated risks, the ability to use the same incisions as those created for cataract surgery, the relative simplicity of the procedure, the theoretical protection against hypotony with downstream episcleral venous resistance, and finally the preservation of conjunctiva should traditional filtration surgery be required later. Although the device shows promise, questions remain. Histologic studies have shown that the footplate of the hand piece effectively protects the outer wall of the canal and collector channel ostia from injury or trauma²¹, but the long-term effect of electrosurgical energy in the angle has yet to be studied effectively from a biochemical or inflammatory mediator standpoint.

With all these conventional outflow augmentation devices, the question of the lowest attainable IOP is relevant; it needs to be considered when selecting an appropriate surgical treatment for an individual patient. While there is no downstream resistance in the subconjunctival space, thus offering no protection in blebs against hypotony, the episcleral venous resistance in theory limits the lowest IOP attainable in these procedures. As a result, patients who require very low target IOPs may not be best served by a conventional outflow procedure.

Technique

A 4 mm fornix-based conjunctival peritomy exposes the sclera 2 mm posterior to the limbus where a 3.5 mm long incision is created. This incision is perpendicular to the surface and near full thickness; the blue hue of the choroid is visible through a thin remaining layer of sclera. A scleral tunnel is then created anteriorly towards the scleral spur but not advanced into clear cornea. After this has been fashioned, a vertical incision into the suprachoroidal space is made at the base of the original linear incision and gentle injection with a blunt cannula of anesthesia and viscoelastic is performed. A paracentesis allows inflation of the anterior chamber with OVD at the planned site of gold shunt entry. A linear entry into the anterior chamber is created at the level of the scleral spur, the location of which can be confirmed by intraoperative gonioscopy.

The gold shunt is gently slid into the scleral pocket until its head is seen in the anterior chamber. Because the channels within the device may be crushed with any blunt force, handling the body of the device is inadvisable. With a 27-gauge hypodermic needle on the surface of the device, it is manipulated into position, or alternatively a Sinskey hook may be used to manipulate the posterior aspect of the shunt via one of its posterior wing holes (Fig. 41.12). Proper positioning of the device requires all of its anterior openings to be visible in the anterior chamber, and with its tail and all of the posterior openings fully in the suprachoroidal space. Once satisfactorily achieved, the sclera is closed in a water-tight fashion with four to five interrupted 10-0 nylon sutures. This is followed by watertight conjunctival closure. OVD is removed from the anterior chamber with a dry technique using a blunt cannula on a syringe half-filled with balanced saline solution.

Fig. 41.12 The gold microshunt in satisfactory position and a 27-gauge hypodermic needle seen nearby is used to manipulate the body of the shunt.

Discussion

The cyclodialysis cleft has been used to lower IOP by augmenting uveoscleral outflow, but has been abandoned due to the unpredictability of results, persistent hypotony as a significant complication, as well as often sudden and dramatic elevations in IOP late postoperatively due to cleft closure. Despite the unpredictability in the creation of a cyclodialysis cleft, several devices including hyaluronic acid implants, Teflon tube implants, hydroxyethyl methacrylate capillary strips, and scleral strips have been attempted as suprachoroidal implants to act as spacers to maintain a cyclodialysis communication^22–25. A Phase III multicenter trial is in progress comparing patients who have failed filtering surgery randomized to receive either the Ahmed GDD or the gold microshunt.

Recently, data on 38 patients with uncontrolled open angle glaucoma patients, with or without prior filtering surgery, have reported a mean IOP decrease from 27.6 mmHg to 18.2 mmHg at a mean follow-up time of 11.7 months, with topical medication numbers falling from 2.0 to 1.5. Complications reported related to the device include synechia formation to the shunt, hyphema, and exudative retinal detachment²⁶. Other shunt-related complications which may occur include shunt–cornea touch, cataract formation, shunt migration, exposure, prolonged anterior chamber inflammation, hypotony, vitreous hemorrhage, and chronic pain.

Technique

After standard phacoemulsification and intraocular lens (IOL) implantation, the ciliary sulcus is inflated with OVD. The endoscopic probe is inserted through the clear corneal cataract incision and the surgeon watches the external monitor. Once the ciliary processes are visualized, the foot pedal is depressed with the aiming beam focused on the posterior tails of the ciliary processes. This shrinks the ciliary processes posteriorly, curling them away from the posterior iris surface (Fig. 41.13). If additional IOP lowering is desired, the anterior aspect of the process may be treated as well, but only after the posterior tail has been ablated and posterior curling of the individual process observed. This is performed for approximately 270°, the approximate maximum permissible arc through a single incision.

Fig. 41.13 Endoscopic cycloplasty. Note the red aiming beam of the diode laser pointed at the tail of the ciliary process as the initial ablation point. The whitened ciliary processes on the right have been ablated while the ones on the left have not yet been treated.

An intraoperative gonioscopic mirror can be used to determine whether peripheral anterior synechiae (PAS) are present. If these are present, anterior segment microforceps (MST Surgical, Redmond, WA) may be used to grasp peripheral iris and release the PAS under gonioscopic visualization (Fig. 41.14). Once completed, automated irrigation and aspiration remove all residual OVD. The irrigation and aspiration hand piece may be used to grasp peripheral iris and exert gentle centripetal tension to release PAS. Care must be taken not to apply excessive centripetal force as this may result in iridodialysis, tearing of the iris root, and/or hyphema. Depending on the amount of PAS present, this may or may not be necessary. Although not well defined, if the cumulative arc degrees of open angle are greater than 180°, goniosynechialysis is unlikely to be necessary.

Fig. 41.14 Goniosynechialysis under view of a goniomirror. The peripheral iris is grasped with anterior segment microforceps and a gonioscopic mirror used to visualize the angle opening (top of the figure). Here the red hue of blood in Schlemm’s canal can be visualized signifying opening of a previously synechial angle closure.

Discussion

While ECP has been reserved for eyes refractory to all other glaucomatous medical, laser, or surgical therapy, this technique, which we have termed ‘endoscopic cycloplasty’ (ECPL), combined with cataract extraction and IOL implantation appears to be effective in opening the angle in angle closure or angle closure glaucoma patients and may have a unique role in the treatment of these sometimes difficult to manage cases. Additionally, this technique has been observed to be successful in the treatment of angle closure secondary to plateau iris, occasionally with dramatic results (Fig. 41.15). As has been previously demonstrated, cataract extraction alone does not relieve a plateau iris configuration and these patients continue to be at risk for angle closure and angle closure glaucoma from this mechanism even when pseudophakic²⁷.

Fig. 41.15 A postoperative anterior segment optical coherence tomography image of a patient who had received phacoemulsification with IOL implantation and nasal 270° treatment with endoscopic cycloplasty. Note the dramatic opening of the angle (left side) as contrasted to the temporal (right side) narrow plateau iris angle configuration.

Although this treatment widens the anterior chamber angle relieving an angle closure component to an individual patient’s glaucoma, one must be careful in patients who may have mixed mechanisms for their elevated IOP. In those patients who have an open angle component to their glaucoma or underlying pathology in the JTM increasing aqueous outflow resistance, even after treatment with cataract surgery combined with endoscopic cycloplasty, the IOP may continue to be elevated and the patient may require additional filtration surgery or an outflow augmentation procedure. Further, should an angle closure patient have advanced visual field loss or dense defects and require a low IOP target, mere relief of a narrow angle configuration may not be sufficient to achieve the target IOP. However, the authors have observed patients with appositional or synechial angle closure of greater than 180° achieve IOPs in the low teens after phacoemulsification and endoscopic cycloplasty and goniosynechialysis.

Potential complications associated with ECP include prolonged or persistent anterior chamber inflammation, inadvertent zonular or capsular injury, inadvertent iris ablation, and hypotony. Potential complications associated with goniosynechialysis include hyphema, iridodialysis, iris tears, cyclodialysis, and Descemet’s injury and detachment. Although a significant concern with cycloablation procedures is persistent hypotony, with the performance of endoscopic cycloplasty for 270° of arc length in conjunction with cataract extraction in a series of 101 consecutive patients, data presented revealed no cases of hypotony at 6 months follow-up²⁸.

In patients with narrow anterior chamber angles, whether due to an anteriorly positioned lens–iris diaphragm or plateau iris mechanism, along with borderline IOP with or without medications and pre-perimetric or early field loss, consideration should be given to performing phacoemulsification and endoscopic cycloplasty to open the anterior chamber angle and decrease aqueous secretion as a method to control IOP prior to subjecting the patient to a conventional bleb-forming procedure. Although patients with underlying open angle glaucoma as part of a mixed mechanism elevation of IOP, or those who have suffered advanced field loss, are not likely to achieve the low target IOP required and may require conventional filtration surgery, this procedure is an effective and relatively safe option to consider in this patient population.