Glaucoma Surgery

Which Surgery to Pick for Your Patient?

      Keywords

      Key points

      • There are 3 main approaches to glaucoma surgery: subconjunctival, Schlemm canal–based, and suprachoroidal/ciliary body.
      • Subconjunctival glaucoma surgery is ideal for patients with advanced disease, low target pressures, and prior failed surgery.
      • Although transscleral cyclophotocoagulation has classically been reserved for patients with refractory glaucoma, micropulse technology might become an indispensable tool used earlier during the disease process, sparing the higher frequency of serious complications of the older technology.
      • Although Schlemm canal–based procedures are usually considered in mild to moderate glaucoma cases with controlled or slightly above-target intraocular pressure and are often combined with cataract surgery, suprachoroidal shunts are still struggling to find their role and currently undergoing further trials to validate their efficacy and safety.
      • Preliminary evidence implies a possible role for some of the newer microinvasive glaucoma surgery in treating patients with prior failed incisional surgery.

      Introduction

      The field of glaucoma has been going through an era of renaissance during the last 2 decades, with a quickly expanding armamentarium of new innovative surgical options adding to the classic filtration surgery.
      Trabeculectomy is generally considered the gold-standard treatment for glaucoma patients and is still considered one of the most effective procedures, although one that is associated with serious possible complications, making many surgeons reconsider its role in the treatment paradigm. Nonpenetrating glaucoma surgery (NPGS) and enhanced versions, such as canaloplasty, also were developed, aiming to increase the safety profile, sometimes at the expense of less efficacy.
      Tube shunts have classically been implemented both after failed glaucoma surgeries and in patients with complex secondary glaucoma cases, which carry a higher risk of failure with trabeculectomy.
      Cyclodestructive procedures have been mainly reserved for refractory glaucoma cases with a very low visual potential. The introduction of micropulse laser technology has reshaped the way many surgeons think of these types of procedures, making them more attractive to perform at an earlier stage of the disease and in patients with good visual potential.
      The term microinvasive glaucoma surgery (MIGS) was coined in 2012 to describe an ab interno procedure, with minimal trauma, efficacy, high safety profile, and rapid recovery [
      • Saheb H.
      • Ahmed I.I.
      Micro-invasive glaucoma surgery: current perspectives and future directions.
      ]. As the safety of these newer glaucoma procedures is thought to be usually superior to classic filtration surgery, usually at the expense of efficacy, the term interventional glaucoma has been suggested to infer surgical intervention to be done earlier in the disease process.
      Many new procedures have been introduced since then, while still grouped under the umbrella of MIGS, although many of them differ in their efficacy and safety profile, and some may be done by an ab externo approach, such as the XEN gel stent or Preserflo microshunt.
      It might be prudent, however, to classify glaucoma-surgical options according to the target site of treatment, namely subconjunctival, Schlemm canal, and the ciliary body/supraciliary space, and not merely as classic versus modern technologies, with the former approach capable of giving a better indication to the degree of efficacy, helping to make surgical decisions, and helping postoperative management.
      In view of this increasing number of surgical instruments in our toolbox, the choice of which tool to choose for which patient might become increasingly more challenging for the glaucoma surgeon, keeping in mind many other important factors, including the level and type of disease, surgeon experience, availability of the different devices, and reimbursement issues.

      Significance

      Many factors come to mind when deciding on which procedure to choose:
      • Age and life expectancy
      • General health status, type of work, comorbid eye disease, and so forth
      • Type of glaucoma
      • Angle status (narrow, closed, open)
      • Lens status (phakic, cataract, pseudophakia, aphakia)
      • Level of glaucoma damage
      • Preoperative IOP
      • Target IOP
      • Refractive status (myopia, presbyopia)
      • Past ocular surgeries and ocular comorbidities
      • Resource availability
      • Reimbursement issues
      Often several surgical options might be found appropriate, or different procedures might be chosen by different surgeons considering the surgeon’s experience and comfort with any given procedure.
      Fig. 1 summarizes the different surgical options available for the glaucoma surgeon.
      Figure thumbnail gr1
      Fig. 1Different approaches to glaucoma surgery. ABiC, ab interno canaloplasty; BANG, bent ab interno needle goniectomy; CW-TSCPC, continuous-wave transscleral cyclophotocoagulation; KDB, Kahook dual blade; OMNI, viscocanaloplasty and ab interno trabeculotomy.

      Subconjunctival surgery

      Fig. 2 summarizes the main indications for the choice of subconjunctival glaucoma surgery.
      Figure thumbnail gr2
      Fig. 2Main indications for the subconjunctival glaucoma approach.
      This route usually is opted for when the patient has uncontrolled disease under maximal tolerated medical therapy, and after possible trial of selective laser trabeculoplasty (SLT) if indicated. Surgeries under this group usually are capable of bringing the intraocular pressure (IOP) into the low-teen values, rendering them a good option to choose in more advanced disease requiring low target pressures, and in patients with very high preoperative IOP.

       When not to opt for subconjunctival surgery?

      Patients with scarred and cicatricial conjunctiva and those with significant ocular surface disease and chronic blepharitis may not be ideal candidates for this route, as healing is often suboptimal, with higher risk of bleb leaks and failure, blebitis, and tube or microstent erosion. Blebs are generally to be avoided if contact lens wear is necessary postoperatively.

       Nonpenetrating glaucoma surgery

      This group includes several techniques, among which the most commonly used techniques today include deep sclerectomy (DS), viscocanalostomy, and canaloplasty.
      DS aims to promote filtration primarily to the subconjunctival space through a thin trabeculo-Descemet membrane (TDM), providing some resistance to outflow. It involves the dissection of a superficial scleral flaplike trabeculectomy, followed by a deeper flap dissection extending anteriorly into clear cornea, on the way to unroofing the outer wall of Schlemm canal, and anteriorly leaving a thin membrane of trabeculo-Descemet thought to be responsible for filtration. The inner wall of Schlemm canal also can be removed with special forceps, possibly augmenting filtration. DS usually is augmented by the use of antifibrotics, such as mitomycin-C (MMC), to enhance the efficacy in the long term.
      co2 laser has been used for ablation of the deep scleral flap and unroofing the Schlemm canal in a procedure called CLASS–co2 laser assisted sclerectomy surgery. This surgery minimizes the risk of perforation as compared with manual deep flap dissection.
      The implantation of a collagen, hyaluronic acid, or Hema implant, under the superficial scleral flap, might be used to keep the patency of the deep intrascleral lake after DS.
      Complications with DS usually are less severe than with trabeculectomy with more rapid visual rehabilitation and less chance of hypotony.
      Possible complications include the following:
      • Microperforations and macroperforations intraoperatively with possible iris incarceration. In the latter case, there is need to convert to a classic trabeculectomy procedure.
      • Insufficient deep flap dissection causing high pressures postoperatively.
      • Postoperative hyphema, which usually absorbs within a few days without complications.
      Laser goniopuncture with Q-switched 532-nm YAG Laser usually is needed in more than half of the cases in order to increase filtration through the TDM window postoperatively, as this structure is prone to scarring in the long run, or in the case of insufficient deep dissection.
      Contraindications:
      • Neovascular glaucoma (NVG)
      • Iridocorneal endothelial (ICE) syndrome
      • Chronic angle-closure glaucoma (relative)
      • Posttraumatic angle recession with extensive damage to the trabecular meshwork (TM)
      Literature on the comparison between NPGS and trabeculectomy has shown contradictory results, because of the different techniques used and different surgeon experience when comparing the 2 techniques.
      A meta-analysis comparing NPGS versus trabeculectomy concluded that DS augmented with MMC was as effective as trabeculectomy with MMC with less postoperative complications. The addition of a subscleral implant was not advisable, as it gave no advantage while raising the complexity and the cost [
      • Gabai A.
      • et al.
      Efficacy and safety of trabeculectomy versus nonpenetrating surgeries in open-angle glaucoma: a meta-analysis.
      ].
      In the authors’ experience, DS is especially beneficial in cases of very high preoperative IOP or patients with high myopia who are at a higher risk of postoperative hypotony after trabeculectomy [
      • Costa V.P.
      • Arcieri E.S.
      Hypotony maculopathy.
      ].
      Viscocanalostomy and canaloplasty are thought to promote filtration through the natural outflow pathway, namely the Schlemm canal. It usually is performed similar to DS, with the main difference being the instillation of cohesive viscoelastic material (Healon GV) into the cut edges of the canal. Canaloplasty is a variation of viscocanalostomy by the addition of Schlemm canal dilation 360 using a microcatheter (iTrack 250) and placement of a permanent suture in the stretched canal (Fig. 3).
      Figure thumbnail gr3
      Fig. 3Two ends of a looped Prolene 10-0 suture are being tied after passing 360° though the Schlemm canal, guided by the iTrack 250 microcatheter, stretching the canal in a canaloplasty procedure.
      These procedures are indicated in patients with primary open-angle glaucoma (POAG) and most of the secondary open-angle glaucomas (OAGs). They are especially beneficial in the authors’ experience in young patients requiring target pressures in the mid- to high-teens, and mechanistically also may increase trabecular and circumferential aqueous outflow.

       Trabeculectomy

      Trabeculectomy has been considered the gold-standard glaucoma surgery for years, since its introduction by Cairns [
      • Cairns J.E.
      Trabeculectomy. Preliminary report of a new method.
      ]. It involves the creation of a scleral flap under which access to the anterior chamber is created to promote creating a subconjunctival bleb. An antimetabolite, such as MMC or 5-Fluorouracil (5-FU), usually is used to prevent excessive scarring and hereby reduces the risk of failure, at the expense of more postoperative complications, such as hypotony and endophthalmitis.
      It is mainly indicated when very low target pressures (single digit) are required, as it possibly has the best chances of achieving this target.
      Care should be taken when operating on highly myopic young patients, as these are more prone to develop hypotony postoperatively.
      Relative contraindications
      • Aphakic glaucoma
      • Active ocular inflammation
      • Thin sclera

       XEN Gel Implant (Allergan Inc, Irvine, CA, USA)

      The XEN implant is a hydrophilic tube composed of a porcine gelatin and cross-linked with glutaraldehyde. It has an external diameter of 150 μm and an internal lumen of 45 μm, which is claimed to provide approximately 6 to 8 mm Hg internal pressure resistance, according to the Hagen-Poiseuille law, and protection against postoperative hypotony [
      • Samples J.R.
      • Ahmed I.I.K.
      Surgical innovations in glaucoma.
      ].
      It can be implanted in an ab interno or ab externo approach, shunting aqueous to the subconjunctival space. The ab externo approach sometimes is preferred when done as a standalone procedure, aiming to create more superior blebs by avoiding the common nasal blebs sometimes created with the ab interno approach with possible bleb dysesthesia afterward.
      The Xen Glaucoma Treatment System was approved in the United States for the management of refractory glaucoma where previous surgical treatment has failed, or in patients with POAG, pseudo-exfoliative (PXE), or pigmentary glaucoma that is unresponsive to maximum tolerated medical therapy. It also has been described for use in juvenile OAG and uveitis patients [
      • Fea A.M.
      • et al.
      XEN..
      ].
      Results from the APEX study have shown success in around two-thirds of the patients at 2 years after standalone or combined phacoemulsification with Xen implantation in POAG [
      • Reitsamer H.
      • et al.
      Two-year results of a multicenter study of the ab interno gelatin implant in medically uncontrolled primary open-angle glaucoma.
      ].
      Another retrospective study comparing standalone Xen implantation versus trabeculectomy has shown comparable risk of failure and safety profile at 1 year with more needling procedures needed in the first [
      • Schlenker M.B.
      • et al.
      Efficacy, safety, and risk factors for failure of standalone ab interno gelatin microstent implantation versus standalone trabeculectomy.
      ].
      The main advantages of the XEN Gel Implant over other filtering procedures include its less-invasive surgical procedure, favorable safety profile, more rapid visual recovery, and short surgical duration, rendering this implant especially appropriate for patients who are unable to tolerate long surgical procedures or when access to operating room time is more limited.

       Preserflo Microshunt (Santen Pharmaceutical Co Ltd, Osaka, Japan)

      The MicroShunt is an 8.5-mm-long microincisional filtration surgery device with a 350-μm outer diameter and 70-μm lumen. It is composed of poly(styrene-block-isobutylene-block-styrene), or SIBS, which is a highly biocompatible, bioinert material. It is implanted via an ab externo approach, allowing hemostasis control, precise placement, and verification of flow. Aqueous humor flows from the anterior chamber to a posterior bleb formed under the Tenon capsule. Several studies have shown promising results for this procedure in reducing IOP and medication burden, although this device is still investigational and not yet approved by the Food and Drug Administration (FDA) [
      • Schlenker M.B.
      • et al.
      Intermediate outcomes of a novel standalone ab externo SIBS microshunt with mitomycin C.
      ,
      • Batlle J.F.
      • et al.
      Three-year follow-up of a novel aqueous humor MicroShunt.
      ].

       Tube shunts

      The use of tube shunts in glaucoma surgery has been largely increasing in the past 2 decades [
      • Arora K.S.
      • et al.
      Use of various glaucoma surgeries and procedures in Medicare beneficiaries from 1994 to 2012.
      ]. Indications for use have been increasing among glaucoma surgeons [
      • Vinod K.
      • et al.
      Practice preferences for glaucoma surgery: a survey of the American Glaucoma Society.
      ].
      Tube shunts involve the insertion of a silicone tube into the anterior chamber, ciliary sulcus, or the pars plana in vitrectomized eyes, connected to an external plate fixated 8 to 10 mm from the limbus, creating a reservoir modulated by the creation of a fibrous capsule several weeks after the procedure, preventing long-term hypotony.
      Tube shunts are divided into valved, such as Ahmed (New World Medical, Rancho Cucamonga, CA, USA), and nonvalved implants, including Baerveldt (Johnson & Johnson, New Brunswick, NJ, USA), Molteno (Katena Products, Parsippany, NJ, USA), and Ahmed ClearPath (New World Medical).
      Tube shunts are usually indicated in several following scenarios:
      • 1
        Patients with previous ocular surgeries, including failed glaucoma surgery. The Tube versus Trabeculectomy study (TVT) was a multicenter randomized controlled trial (RCT) that compared the safety and efficacy of these 2 procedures in eyes with previous ocular surgeries. The trabeculectomy group had a higher rate of failure at 5 years, with higher rates of early postoperative complications.
      • 2
        High risk for trabeculectomy failure, such as in NVG, chronic or recurrent uveitis, ICE syndrome, and pediatric glaucoma.
      • 3
        Patients with scarred conjunctiva owing to ocular cicatricial pemphigoid, Stevens Johnson syndrome, and so forth.
      Pooled data analysis from the Ahmed Baerveldt Comparison study and the Ahmed versus Baerveldt study comparing the valved Ahmed FP7 to the nonvalved Baerveldt 350-mm2 has shown that the latter was more effective and less likely to fail at 5-year follow-up, at the expense of higher rates of postoperative hypotony [
      • Christakis P.G.
      • et al.
      Five-year pooled data analysis of the Ahmed Baerveldt comparison study and the Ahmed versus Baerveldt study.
      ].
      As the nonvalved implants need to be restricted to flow during the first 4 to 6 weeks after surgery to prevent hypotony, this makes the valved implants a more attractive choice when a need exists for immediate reduction of extremely high IOPs, such as the case in NVG, whereas the nonvalved implants may be a better choice when lower target pressures are required in the long term.
      Possible complications associated with tube shunts include endothelial cell loss and persistent corneal edema, diplopia, tube erosion, and persistent hypotony.
      When examining tube shunts as an initial glaucoma procedure, the Primary TVT study has shown similar failure and complications rates at 3 years for trabeculectomy and Baerveldt-350 mm2, with lower IOP and medication use in the trabeculectomy arm. As the options for secondary operation after a failed tube are usually more limited, tube shunts may be less suitable to choose as a primary procedure in low-risk glaucoma patients.

      Cyclodestructive procedures

      Transscleral diode cyclophotocoagulation (TSCPC) classically has been used in refractory glaucoma patients with a guarded visual prognosis. It employs the use of an external diode handpiece to ablate the ciliary body’s secretory cells, therefore reducing the IOP. As these cells have regenerative potential, sometimes several treatments must be used to get the desired effect. Two main modes of external laser delivery are currently in practice: continuous wave (CW-TSCPC) and micropulse transscleral laser treatment (MP-TLT).
      With CW-TSCPC, usually 18 to 24 spots are treated at around 1.2 mm from the limbus, sparing the 3 and 9 o’clock, where the ciliary nerves lie. Serious complications, such as VA loss of more than 2 Snellen lines, intractable inflammation, persistent hypotony, and phthisis, may ensue, making it an option mainly for refractory glaucoma after other options have failed.
      The MP-TLT is a relatively new technology delivering treatment in duty cycles with periods of rest, thereby reducing collateral tissue necrosis and giving a better safety profile.
      In a randomized exploratory study comparing the 2 modes in refractory glaucoma, both reduced the IOP similarly by 45%, with no significant difference in re-treatment rates or number of IOP-lowering medications. The ocular complication rate was higher in continuous wave–treated eyes, although a higher prevalence of NVG cases was noted in this group.
      Finally, an ab interno approach to cyclodestruction can be done using the endoscopic cyclophotocoagulation (ECP) probe, which is usually done in combination with a cataract surgery, for mild to moderate glaucoma patients requiring additional IOP control or medication reduction. The only RCT described on ECP was published lately comparing phaco-ECP to phaco only in primary angle-closure glaucoma (PACG) patients, showing a mild additional reduction of IOP and medication use at 24 months in the treatment arm [
      • Tóth M.
      • et al.
      Endoscopic cyclophotocoagulation (ECP) for open angle glaucoma and primary angle closure.
      ].

      Schlemm canal–based procedures

       Selective laser trabeculoplasty

      SLT is a 532-nm Q-switched frequency-doubled neodymium-YAG laser aiming to increase trabecular outflow through several possible mechanisms. It is known to decrease the pressure by around 25% to 30% as a primary treatment, and to a variable extent in different other scenarios [
      • Garg A.
      • et al.
      Primary selective laser trabeculoplasty for open-angle glaucoma and ocular hypertension: clinical outcomes, predictors of success, and safety from the laser in glaucoma and ocular hypertension trial.
      ]. It usually is performed 360° under gonioscopic view, in one or multiple sessions.
      Main indications
      • 1
        Ocular hypertension
      • 2
        POAG and normal-tension glaucoma
      • 3
        PXE glaucoma
      • 4
        Pigmentary glaucoma
      • 5
        Primary angle closure (PAC)/PACG with patent iridectomy and visible angle at least 180°
      • 6
        Steroid-induced glaucoma
      This type of treatment usually is well tolerated, with very rare serious complications. One should beware in cases of pigmentary glaucoma owing to a higher rate of IOP spikes [
      • Harasymowycz P.J.
      • et al.
      Selective laser trabeculoplasty (SLT) complicated by intraocular pressure elevation in eyes with heavily pigmented trabecular meshworks.
      ].
      It can be presented at any stage of the disease with possible supplementary additive effect on IOP control. It can be done on phakic and pseudophakic patients, although some evidence has suggested some attenuated response in the early posttreatment period in pseudophakic patients [
      • Shazly T.A.
      • et al.
      Effect of prior cataract surgery on the long-term outcome of selective laser trabeculoplasty.
      ].
      Contraindications:
      • 1
        Uncontrolled uveitic glaucoma
      • 2
        NVG
      • 3
        Poor visualization of the TM

       Schlemm canal–based microinvasive glaucoma surgery

      Fig. 4 shows some examples of various MIGS procedures classified by their target route of treatment.
      Figure thumbnail gr4
      Fig. 4Minimally invasive glaucoma surgery targeting different routes of filtration. (upper left to lower right) iStent G1, BANG, iStent inject, ab interno trabeculotomy using a Prolene 5-0 suture, micropulse CPC, hydrus, and ab interno Xen implantation. CPC, cyclophotocoagulation.
      In humans, 75% of the resistance to aqueous humor outflow is thought to occur at the level of the TM, where most of this resistance is supposed to stem from the juxtacanalicular meshwork [
      • Gillmann K.
      • Mansouri K.
      Minimally invasive glaucoma surgery: where is the evidence?.
      ,
      • Grant W.M.
      Further studies on facility of flow through the trabecular meshwork.
      ]. Mounting evidence has shown that the resistance to outflow is more complex and consists of 3 different levels contributing to the total resistance: loss of permeability of the TM, collapse of the Schlemm canal, and downstream distal resistance [
      • Maepea O.
      • Bill A.
      Pressures in the juxtacanalicular tissue and Schlemm's canal in monkeys.
      ]. Therefore, any procedure targeting any of these levels aims to augment the physiologic outflow through the conventional pathway that usually is impaired in patients with glaucoma. Although these procedures are known to have a higher safety profile than classic filtration surgery, their IOP-lowering efficacy usually is restricted to the episcleral venous pressure (EVP) at best, and their long-term results are far from being known.
      These types of procedures as MIGS in general are usually approved by the FDA for implantation in conjunction with cataract surgery in patients with mild to moderate glaucoma, although in other countries, they might be used as stand-alone procedures, even in severe disease [
      • Andrew N.H.
      • Akkach S.
      • Casson R.J.
      A review of aqueous outflow resistance and its relevance to microinvasive glaucoma surgery.
      ].
      Procedures falling under this category can be subdivided into subcategories according to their mechanism of action:
      • 1
        Removal of the TM and inner wall of Schlemm canal
      • 2
        Disruption of the TM and inner wall of Schlemm canal
      • 3
        Implantation of a microstent to bypass the TM
      • 4
        Dilation of Schlemm canal via an internal approach
      Table 1 summarizes the main techniques used in either of the aforementioned subcategories, with relevant data on their safety and efficacy from select relevant studies.
      Table 1Minimally invasive glaucoma surgery, techniques, and efficacy
      Removal of the trabecular meshwork and inner wall of Schlemm canal (ab interno trabeculectomy)
      DeviceManufacturerDesign and techniqueEfficacy
      TrabectomeNeoMedix, Tustin, CA, USASingle-use electrocautery handpiece with irrigation and aspiration unit, for removal of 60°–120° of the trabecular meshworkInconclusive results regarding efficacy

      Seventy-eight percent of patients achieve IOP between 6 and 15 mm Hg and at least 20% IOP reduction without medications when combined with phaco at 2 y according to 1 report [
      • Nichani P.
      • et al.
      Micro-invasive glaucoma surgery: a review of 3476 eyes.
      ]
      Kahook Dual BladeNew World Medical, Rancho Cucamonga, CA, USASingle-use disposable blade with a sharp tip, which is used to pierce the trabecular meshwork, a ramp which stretches the trabecular meshwork, and dual parallel blades, which create paired parallel incisions in the trabecular meshworkPhaco combined Kahook Dual Blade might be at least as effective as phaco-iStent for reducing IOP and medication burden [
      • Le C.
      • et al.
      Surgical outcomes of phacoemulsification followed by iStent implantation versus goniotomy with the Kahook dual blade in patients with mild primary open-angle glaucoma with a minimum of 12-month follow-up.
      ,
      • ElMallah M.K.
      • et al.
      12-month retrospective comparison of Kahook dual blade excisional goniotomy with iStent trabecular bypass device implantation in glaucomatous eyes at the time of cataract surgery.
      ]
      Bent AbInterno Needle GoniectomyTrabeculotomy using the bent tip of a 25-gauge needleNo long-term data available
      Disruption of the trabecular meshwork and inner wall of Schlemm canal (ab interno trabeculotomy)
      DeviceManufacturerDesign and technique
      Gonioscopy-assisted transluminal goniotomy (GATT)Ellex iScience, Fremont, CA, USATrabeculotomy 180°–360° using a 250-μm iTrack microcatheter with a fiberoptic tip advanced through the canal

      Trabeculotomy 360° using a Prolene 5-0 suture
      Efficacy reported in primary, secondary, and juvenile open-angle glaucoma and prior incisional glaucoma surgery [
      • Grover D.S.
      • et al.
      Gonioscopy assisted transluminal trabeculotomy: an ab interno circumferential trabeculotomy for the treatment of primary congenital glaucoma and juvenile open angle glaucoma.
      ,
      • Grover D.S.
      • et al.
      Outcomes of gonioscopy-assisted transluminal trabeculotomy (GATT) in eyes with prior incisional glaucoma surgery.
      ]

      Younger age may be predictive of success [
      • Salimi A.
      • et al.
      Gonioscopy-assisted transluminal trabeculotomy in younger to middle-aged adults: one-year outcomes.
      ]
      Trab360/OMNISight Sciences, Menlo Park, CA, USASingle-use handpiece with a microcatheter advancing from the tip allowing 2 opposite 180 trabeculotomies
      Implantation of a microstent to bypass the trabecular meshwork
      DeviceManufacturerDesign and technique
      iStent G1Glaukos Corporation, San Clemente, CA, USASnorkel-shaped heparin-coated, nonferromagnetic titanium stent

      Central inlet: 120 μm
      At 48 mo follow-up, a 14.2% between-group difference in favor of the combined iStent-phaco group vs phaco-only group was statistically significant for mean IOP reduction, compared with the phaco-only group, with a significant reduction in number of medications in both arms [
      • Fea A.M.
      • et al.
      Micro-bypass implantation for primary open-angle glaucoma combined with phacoemulsification: 4-year follow-up.
      ]
      iStent inject-WGlaukos Corporation, San Clemente, CA, USABullet-shaped heparin-coated, nonferromagnetic titanium stent

      Inject: 0.36 width × 0.23 height

      Central inlet: 80 μm

      Inject: W: 0.36 mm width × 0.36 height

      Central inlet: 80 μm
      At 24 mo, 75.8% of phaco-iStent inject eyes vs 61.9% of control phaco only eyes experienced ≥20% reduction from baseline in unmedicated IOP, while 83% of treatment arm achieving target unmedicated [
      • Samuelson T.W.
      • et al.
      Prospective, randomized, controlled pivotal trial of an ab interno implanted trabecular micro-bypass in primary open-angle glaucoma and cataract: two-year results.
      ]
      HydrusIvantis Inc, Irvine, CA, USABiocompatible nitinol 8-mm-long trabecular bypass device with 3 openings

      Increases trabecular outflow and scaffolds the Schlemm canal
      At 24 mo, 77% of open-angle glaucoma patients achieved 20% or more decrease in unmedicated IOP after phaco-Hydrus compared with 57.8% in the phaco-alone group, with 1.4/1 medication reduction, respectively [
      • Samuelson T.W.
      • et al.
      A Schlemm canal microstent for intraocular pressure reduction in primary open-angle glaucoma and cataract: the HORIZON study.
      ]
      Dilation of Schlemm canal via an internal approach
      DeviceManufacturerDesign and technique
      Ab Interno CanaloplastyiTrack microcatheter inserted through a small goniotomy and passed 360° with viscodilation on retractionWhen compared with Hydrus, both implants allowed significant IOP reductions, with comparable rate of clinical success and safety profile [
      • Gandolfi S.A.
      • et al.
      Comparison of surgical outcomes between canaloplasty and Schlemm's canal scaffold at 24 months' follow-up.
      ]
      VISCO360/OMNISight Sciences, Menlo Park, CA, USAOMNI system combines the TRAB360 with the VISCO360
      Patients who are usually found suitable for these types of procedure include the following:
      • 1
        Patients well controlled or slightly above target under medical treatment presenting for cataract surgery
      • 2
        Patients with OAG mainly owing to trabecular dysfunction, including patients with PXE and pigment-dispersion glaucoma, and select cases of angle-closure glaucoma
      • 3
        Patients willing to reduce burden of medical treatment owing to cost, comfort, or tolerance issues
      • 4
        Patients with uncontrolled pressures found inapt to undergo subconjunctival surgery
      Patients less suitable to undergo of these procedures include the following:
      • 1
        Patients with high EVP, such as Sturge-Weber syndrome
      • 2
        Patients who perform Valsalva maneuver very often, such as heavy weight-lifters, because of the increased risk of recurrent hyphemas mainly after excisional procedures
      • 3
        Patients with active ocular inflammation
      • 4
        Phakic patients with angle closure as a standalone procedure
      • 5
        Patients requiring low target IOPs
      • 6
        Multiple drug allergies precluding possible additional glaucoma medications postoperatively
      Because of the paucity of large RCTs reporting on the efficacy and safety of different procedures and long-term effects, including clinical parameters other than IOP, it is difficult to draw firm conclusions on the efficacy of different MIGS procedures. In a recent large review of MIGS procedures summarizing the accumulating evidence on the efficacy and safety of MIGS procedures, certain conclusions possibly can be made [
      • Nichani P.
      • et al.
      Micro-invasive glaucoma surgery: a review of 3476 eyes.
      ]:
      • 1
        Phaco-MIGS procedures in general achieved higher mean reduction of IOP and postoperative medications relative to control.
      • 2
        iStent as a standalone procedure is more effective than medication alone and reduces postoperative medication use.
      • 3
        Implanting a second iStent adds to the IOP reduction, while implanting a third has a less pronounced additive effect.
      • 4
        Hydrus standalone procedure performs better when compared with iStent or ABiC.
      • 5
        Data regarding other Schlemm canal–based surgeries were less conclusive, and some did not meet the quality criteria set by the researchers.
      Complications associated with these types of procedures mostly include different degrees of hyphema (generally less severe with the TM-bypass procedures), inflammation, stent obstructions, peripheral anterior synechiae (PAS) formation, and less commonly, vision loss.

      Suprachoroidal

      Suprachoroidal MIGS usually are implanted ab interno under clear corneal incision, into the suprachoroidal space, and can be combined with cataract surgery. The only device that was FDA approved for use is the CyPass Micro-Stent (Alcon Laboratories Inc, Fort Worth, TX, USA), which was voluntarily withdrawn in 2018 because of issues concerning endothelial cell loss at 5-year follow-up data.

      CyPass (Alcon, Fort Worth, TX, USA)

      This implant is 6.35 mm long with an outer diameter of 430 μm, an inner diameter of 300 μm, and with 76-μm fenestrations along the length of the device. It is implanted under clear corneal incision, using a guidewire advancing it to the scleral spur under gonioscopic view, where it is passed after blunt dissection with the guidewire into the supraciliary space. Three retention rings at the proximal end of the implant help to keep the implant in place.
      The implant was mainly indicated in patients with mild to moderate POAG in conjunction with cataract surgery.
      Two-year data from the COMPASS trial revealed compelling efficacy with 7.4-mm Hg mean IOP reduction from unmedicated preoperative IOP, with 85% of patients off glaucoma medications. Seventy-seven percent of the phaco-CyPass treatment arm and 60% of the phacoemulsification control arm achieved an unmedicated IOP reduction of ≥20% at 2 years [
      • Vold S.
      • et al.
      Two-year COMPASS trial results: supraciliary microstenting with phacoemulsification in patients with open-angle glaucoma and cataracts.
      ].
      Possible complications of the procedure include hypotony, IOP spikes, hyphema, device occlusion, device malposition, and VA loss.
      Later unpublished data from the COMPASS-XT study have shown a significant ECL loss in the phaco-CyPass group at 5-year follow-up, with ECL loss correlated to the length of the tube in the anterior chamber [
      • Reiss G.
      • et al.
      Safety and effectiveness of CyPass supraciliary micro-stent in primary open-angle glaucoma: 5-year results from the COMPASS XT study.
      ].

       MINIject (iSTAR Medical, Isnes, Belgium)

      The MINIject (iSTAR Medical, Isnes, Belgium) is a biocompatible porous silicone implant built for optimal tissue integration aiming to reduce fibrosis.

       iStent Supra (Glaukos, San Clemente, CA, USA)

      The iStent Supra (Glaukos, San Clemente, CA, USA) is a 4-mm implant made from polyethersulfone and titanium, with a 165-μm heparin-coated lumen, planned for ab interno implantation.
      Both devices use the suprachoroidal outflow pathway and are still awaiting FDA approval.

      Special considerations

       Patients with very advanced disease

      The risk of long-term vision loss after classic filtration surgery, such as trabeculectomy, has been estimated to be up to 7% in some studies. Risk factors include preoperative split fixation and postoperative choroidal effusions with eventual resolution [
      • Francis B.A.
      • et al.
      Vision loss and recovery after trabeculectomy: risk and associated risk factors.
      ]. As the risk for postoperative choroidal effusions is present even with the less-invasive subconjunctival procedures, the use of Schlemm canal–based procedures, even at the expense of less IOP reduction, might be a safer choice, in patients with very diffuse visual field loss and residual central islands of vision.

       Patients with very high intraocular pressure

      Some patient populations are considered high risk for the development of choroidal effusions and suprachoroidal hemorrhage, 2 potentially devastating complications after filtration surgery. These patients include those with systemic hypertension and tachycardia, using anticoagulant or antiplatelet therapy, having very high preoperative IOP, or high EVP. Preventing hypotony in this particular population is of special importance, in order to reduce the risk of development of these 2 serious complications. Choosing procedures with lower risk of hypotony and choroidal detachment should be of high priority in these patients [
      • Schrieber C.
      • Liu Y.
      Choroidal effusions after glaucoma surgery.
      ].
      Fig. 5 summarizes some preferred options for treatment in this subset of patients.
      Figure thumbnail gr5
      Fig. 5Recommended procedures in patients with risk for choroidal detachment.

       Patients with angle-closure glaucoma

      Most of the previously described surgical options are indicated in patients with OAG, whereas some of the procedures might not be an option for patients with angle closure.
      Patients with angle closure are usually classified into the 3 following groups [
      • Foster P.J.
      • et al.
      The definition and classification of glaucoma in prevalence surveys.
      ]:
      • Primary angle-closure suspect (PACS)
      • PAC
      • PACG
      Laser peripheral iridectomy (LPI) classically has been the treatment of choice in patients with PACS, mainly for the prevention of acute angle closure (AAC) glaucoma crisis and progression to PAC.
      It is mostly a benign procedure, although with possible short-term and long-term side effects, such as iritis, pressure spikes, cataract formation, and dysphotopsias.
      The Zhongshan Angle Closure Prevention (ZAP) trial was the first RCT examining the effect of LPI on PACS progression compared with observation [
      • He M.
      • et al.
      Laser peripheral iridotomy for the prevention of angle closure: a single-centre, randomised controlled trial.
      ].The study concluded that LPI had a limited, although significant, prophylactic effect on progression of PACS to PAC, advising against the widespread use of LPI in this setting. Notably, the restriction of the population study to Chinese population and other methodology issues might preclude the generalization of the study results to all the patients with PACS.
      The decision to treat should be made on an individual basis. Factors supporting treatment with LPI include the following:
      • Patients with symptoms characteristic of intermittent or impending episode of AAC
      • Patients with low compliance to treatment and follow-up
      • Patients with AAC in the fellow eye
      • Patients with family history of angle-closure glaucoma
      • Patients with retinal disease necessitating frequent fundus examinations

       Primary angle closure

      Phacoemulsification is especially useful in PAC and PACG patients associated with cataract, as it not only helps improve vision by removing the cataract but also helps to significantly reduce IOP and improve angle parameters.
      The EAGLE trial included patients with PAC or mild to moderate PACG patients aged 50 years and older, with pressures greater than 30 mm Hg but no cataracts, who were randomized to clear lens extraction or LPI. Patients who underwent clear lens extraction had lower pressures, had more open angles, and needed less glaucoma medications and later surgical interventions than the laser group. In addition, the cost-effectiveness of treatment and the patients’ quality of life were slightly better in the phaco group [
      • Azuara-Blanco A.
      • et al.
      Effectiveness of early lens extraction for the treatment of primary angle-closure glaucoma (EAGLE): a randomised controlled trial.
      ].
      In general, older patients with PAC and PACG, especially if they have cataractous lens changes and or presbyopia, are now being offered earlier lens extraction as an option to treat their condition, although discussion with the patient is warranted if they do not have the same inclusion criteria as those in the Eagle study.

       Primary angle-closure glaucoma

      In this subtype of patients, glaucomatous damage is already evident, associated with PAS formation and or high IOP. As noted before, phacoemulsification alone might be sufficient to decrease the IOP to target and is known by itself to improve the angle parameters, anterior chamber depth, and PAS extent.
      Goniosynechiolysis (GSL) is another tool that might be combined with the phacoemulsification procedure, especially when a significant amount of anterior synechiae is still present during intraoperative gonioscopy after the cataract is removed [
      • Ahmed I.I.K.
      • Durr G.M.
      Goniosynechialysis … to release or not to release? That is not the question.
      ]. Combining GSL to phacoemulsification seems to be superior to phacoemulsification alone and comparable to trabeculectomy or phacotrabeculectomy in terms of IOP reduction in chronic angle-closure patients [
      • Liu Y.
      • et al.
      Systematic review and meta-analysis of comparing phacoemulsification combined with goniosynechialysis to other mainstream procedures in treating patients with angle-closure glaucoma.
      ].
      GSL can be done during phacoemulsification surgery using cohesive viscoelastic alone, cyclodialysis spatula, or microinstruments to pull the peripheral iris in the anterior-posterior axis. Possible complications include postoperative inflammation, hyphemas, iridodialysis/cyclodialysis formation, and possible corneal damage.
      Angle-based MIGS also might play a role in patients with PACG. A more recent article compared phacoemulsification with injection of 2 iStents (G1 or inject) to phacoemulsification alone, in patients with PACG. The former intervention yielded significantly greater reductions in IOP and medication use and was more protective against early postoperative IOP spikes [
      • Salimi A.
      • Abu-Nada M.
      • Harasymowycz P.
      Matched cohort study of cataract surgery with and without trabecular microbypass stent implantation in primary angle-closure glaucoma.
      ].

       Patients with neovascular glaucoma

      The aim of the treatment in this case is usually multifaceted. Proper treatment for the cause of ischemia-producing angiogenic factors, usually with panretinal photocoagulation and anti-VEGF injections, should be provided alongside treatment for controlling IOP.
      This diagnosis is usually a harbinger of a poor prognosis, and the glaucoma may be refractory to treatment.
      For control of their glaucoma, medical treatment might be enough. In more advanced cases, intervention usually in the form of tube shunts or cyclodestructive procedures should be done.
      Often patients with good visual acuity have a valved glaucoma drainage device (GDD; eg, Ahmed) implanted because of the immediate reduction of IOP and lower chance of hypotony and risk of choroidal effusion given the high preoperative pressures.
      Patients with low visual potential more often are treated with cyclodestructive procedures, usually with TSCPC. MP-CPC also might be a viable option in both scenarios. A recent study has shown promising results for high-energy MP-CPC with adjunctive use of intravitreal ranibizumab with a good durable effect until 24 months without serious complications.
      Fig. 6 proposes a simplified approach for the choice of the right glaucoma procedure. As mentioned earlier, many other factors should be balanced into the equation, and various surgical options might fit into the same clinical scenario at the discretion of the glaucoma surgeon according to his/her experience.
      Figure thumbnail gr6
      Fig. 6Flowchart for the choice of primary surgery in the glaucoma patient. MTMT, maximally tolerated medical treatment; Trabeculectomy.

       Reoperation after failed glaucoma surgery

      Glaucoma is a chronic disease associated with successes and failures. It is like a rollercoaster with many ups and downs, where each sudden turn is associated with increased emotional load for both the surgeon and the patient.
      The biggest dilemma each glaucoma surgeon faces is what to do when the primary glaucoma surgery fails, especially when even maximally tolerated medical therapy cannot bring the pressure down into the target pressures zone.
      In deciding on successive glaucoma surgeries, the same factors described earlier should be kept in mind with adjustments made as required. In addition, one should strongly consider switching to another route of filtration, as choosing the same route might bring about the same factors causing failure in the first place.
      The following are 3 different scenarios any experienced glaucoma surgeon will encounter:
      • 1
        Failed conjunctival surgery:
        • If the first surgery is salvageable, it might be wise to save the resting conjunctiva for later options and try to perform needling or revision of the bleb with injection of antifibrotics to increase the chances of success. Reports about revision of trabeculectomy surgery have yielded good long-term results [
          • Coote M.A.
          • et al.
          Posterior revision for failed blebs: long-term outcomes.
          ].
        • If the first operation is not salvageable, as in the case of high risk for postoperative leak because of an ischemic bleb or very scarred conjunctiva, then one should think about performing another type of conjunctival surgery if the condition of the conjunctiva allows, and in any case, performing a tube surgery should be strongly advised, as the chances of success might be higher with this type of surgery, as reported in earlier studies.
        • Angle surgery also might be an option to be considered. Gonioscopy-assisted transluminal trabeculotomy (GATT) was shown to be safe and successful in treating 60% to 70% of open-angle patients with prior incisional glaucoma surgery, including trabeculectomy and tube shunts in 1 retrospective study [
          • Grover D.S.
          • et al.
          Outcomes of gonioscopy-assisted transluminal trabeculotomy (GATT) in eyes with prior incisional glaucoma surgery.
          ].
      • 2
        Failed angle surgery:
        • Early failure of a Schlemm canal–based surgery might indicate a diseased distal outflow rendering a second-angle surgery less plausible. In the case of a later failure, another angle-based operation might be not feasible, as in the case of removal of large portions of the TM in GATT surgery.
        • Similarly, after trabectome surgery in which only part of the TM is excised, treating the rest of available TM with SLT, has shown a very limited duration of significant IOP-lowering effects with low success rates [
          • Töteberg-Harms M.
          • Rhee D.J.
          Selective laser trabeculoplasty following failed combined phacoemulsification cataract extraction and ab interno trabeculectomy.
          ]. A histopathologic study comparing changes after iStent, which spans a very limited area of the TM, when compared with specimens from normal and glaucoma human TM tissues showed histopathologic changes adjacent to the location of implants consistent with inflammation and scarring [
          • Capitena Young C.E.
          • et al.
          Histopathologic examination of trabecular meshwork changes after trabecular bypass stent implantation.
          ], a fact that might preclude a second-angle surgery spanning the nasal angle. In this case, one might opt directly for the subconjunctival route or ciliary body procedures, as they have a higher chance of success.
      • 3
        Failed tube surgery:
        • In this case, there are several options to consider:
          • If the tube is thought to be functioning, but to a limited extent, one might try flushing the tube with saline or viscoelastic using a 30-cc syringe via an ab interno or externo approach
          • Revision of the bleb over the tube with excision of the capsule restricting flow
          • Replacement of valved implant to a nonvalved implant
          • Insertion of a second tube in an opposite quadrant
          • Performing CPC laser. One study comparing this technique to insertion of a second tube has shown a superior long-term efficacy for CPC with more VA conservation at 12 months, but with more secondary interventions needed [
            • Schaefer J.L.
            • et al.
            Failed glaucoma drainage implant: long-term outcomes of a second glaucoma drainage device versus cyclophotocoagulation.
            ]. The American Glaucoma Society (AGS) is sponsoring a trial to compare a second Baerveldt shunt to diode cyclophotocoagulation (the ASSISTs trial [AGS Second aqueous Shunt Implant vs TransScleral Treatment Study]).
          • Performing Schlemm canal procedures. One study reported a success rate of 84% at 12 months after trabectome surgery for a failed tube surgery [
            • Mosaed S.
            • et al.
            Results of trabectome surgery following failed glaucoma tube shunt implantation: cohort study.
            ]. Similar success rates have been described as mentioned earlier with the GATT procedure after incisional surgery.
          • Limited reports have described the use of a retrobulbar shunt device connecting the anterior chamber into the retrobulbar space, although it is not yet commercially available and is undergoing further studies [
            • Sponsel W.E.
            • et al.
            Efficacy of a novel retrobulbar extension shunt to rescue eyes with fibrotic encapsulated blebs and uncontrolled ocular hypertension.
            ].
      As data on the failed tube management are mainly from reported retrospective case series, it is difficult to draw conclusions on the efficacy of each surgical intervention, and the decision for intervention should be done on an individual basis (Box 1).
      Re-treatment options after failed primary surgery
      • Failed subconjunctival
        • Bleb revision
        • GDD
        • Schlemm canal–based
        • Ciliary body/suprachoroidal
      • Failed angle
        • Subconjunctival
        • Ciliary body/ suprachoroidal
      • Failed GDD
        • Tube revision
        • Implant replacement
        • Second GDD
        • Ciliary body/suprachoroidal
        • Schlemm canal–based
        • Retrobulbar shunt

      Current relevance and future avenues

      The surgical treatment of glaucoma has seen a huge revision in the past 2 decades, with the addition of incremental tools in the surgical repertoire. The choice of which surgery to do after medications or laser trabeculoplasty can be less straightforward than it has been once, because of the more abundant options to choose from, sometimes with overlapping indications to use.
      Subconjunctival surgery with trabeculectomy as the classic representative, tube shunts as the classic opponent, and other less penetrating candidates on the way, have proven to be the most efficacious route of IOP reduction, usually with a higher complication rate and opted for when more significant intervention is needed. This route of intervention has seen the increase of modern representatives, such as the Xen implant and Preserflo microshunt, which are undergoing major evaluation to elucidate their exact role and share in the overall picture, with very promising preliminary results. Furthermore, new devices have been designed lately that aim to add more controlled postoperative course, possibly preventing hypotony after nonvalved tube shunts. The EyeWatch (Rheon Medical, Lausanne, Switzerland) is one such device, composed of a deformable silicone tube, which drains aqueous humor to a nonvalved implant, such as Baerveldt. Resistance to flow can be adjusted using a magnetic pen laid and rotated externally over the implant, which contains a magnetic disk that controls the compressibility of the draining tube and hereby the resistance to outflow.
      The introduction of Schlemm canal–based MIGS into the glaucoma surgeon’s life has made a huge update to the capabilities of intervening at an earlier stage with a well-predictable high safety profile, even at the expense of reduced efficacy. The physiologic outflow pathway that is usually the endpoint for damage in most glaucoma diagnoses seems like a very natural factor to target, with many procedures aiming to bypass or eliminate this impediment to natural outflow, usually in combination with phacoemulsification surgery. Although many of these procedures may be either modest in effect and duration or awaiting more evidence-based data to support their role, the ability to introduce them at an earlier stage with the possibility to buy time on the long journey with our glaucoma patients may be beneficial. Delaying more significant surgery with several failed “safer” procedures, however, may result in higher cost and progression of the disease with irreversible visual field loss.
      The ability to predict which patient might respond best to these types of procedures should be the focus in the years to come. Aqueous angiography is one of these lately described invasive methods of visualizing the distal outflow pathways, which might prove indispensable in predicting treatment response to different Schlemm canal–based procedures. Future advances might lead to the development of less invasive methods of visualizing the distal outflow structures.
      The suprachoroidal pathway for glaucoma treatment is another route of target that has been examined over the years. The Gold shunt was 1 promising example of such device, but unfortunately has been plagued by high rates of failure because of fibrosis. CyPass was another device pulled off the market because of safety issues concerning the corneal endothelium, which has elevated the need for more long-term safety-focused research on different MIGS procedures. Other new devices described above, some of which were designed to address the issues of reduced fibrosis, need to be examined in the coming years to show their potential efficacy and safety.
      Among these 3 routes of interventions, less-invasive laser treatment options exist that target the different outflow pathways and should be considered along the treatment spectrum whenever indicated. SLT has been used more often as a primary treatment, even replacing medications, in suitable glaucoma patients, in the shadows of the LiGHT study published recently. It comes with a very high safety profile, short-term efficacy, which might buy time in many different scenarios [
      • Gazzard G.
      • Konstantakopoulou E.
      • Garway-Heath D.
      • et al.
      Selective laser trabeculoplasty versus eye drops for first line treatment of ocular hypertension and glaucoma (LiGHT): a multicentre randomised controlled trial.
      ]. Newer SLT platforms exist, such as the Direct Selective Laser Trabeculoplasty (BELKIN Laser Ltd, Yavne, Israel), which provide automated noncontact SLT treatment delivered transsclerally, providing shorter treatment courses with preliminary comparable results to the conventional delivery method [
      • Geffen N.
      • et al.
      Transscleral selective laser trabeculoplasty without a gonioscopy lens.
      ].
      The introduction of MP-TLT has possibly changed the notion of keeping cyclodestructive interventions until later in the disease process, when all other options have been exhausted, and might integrate nicely in different scenarios along the spectrum, although it awaits firmer data from RCTs to pinpoint its exact role. Still, care should still be taken when using this procedure early on, as it might prove to affect the success of later surgical intervention, because of its proinflammatory potential [
      • Tan N.Y.Q.
      • et al.
      Transscleral cyclophotocoagulation and its histological effects on the conjunctiva.
      ]. Time will tell if it is going to replace the older G-probe TSCPC treatment, which has been traditionally saved for refractory neovascular or chronic glaucoma patients with low visual potential, giving results ranging from inefficacy and need for repeated treatments, and rarely, phthisis bulbi.
      Cataract surgery has been offered more commonly to patients with PAC or PACG. Apart from the EAGLE study, several studies have shown the superiority of early cataract surgery to LPI in preventing IOP increase after AAC and improving angle parameters in these patients [
      • Lam D.S.
      • et al.
      Randomized trial of early phacoemulsification versus peripheral iridotomy to prevent intraocular pressure rise after acute primary angle closure.
      ]. Together with the ZAP trial, which has shown LPI to be not cost-effective and recommended against its routine use for in PACS patients, it would be interesting to see the changing trends of LPI use by glaucoma practitioners over the next years.
      Patients with failed glaucoma surgeries pose a rising burden on the system, challenging the glaucoma surgeon faced with the diminishing options. The classic Trab-Tube-CPC pathway has been challenged recently with the rising new treatment options, with limited data on the utility of different options in re-treatment. Again, it might be wise to consider less-invasive methods along the way even at the expense of reduced or short-term efficacy, as the journey is long, and opting for more invasive traditional surgery, such as tube shunts, might considerably limit options in the case of failure. As mentioned before, the ASSIST study is a running study aiming to better understand our mode of action in the case of a failing tube.
      That said, many new devices are on the way, some of them using different routes to reduce the IOP. One such device, the Beacon Aqueous Microshunt (MicroOptx, Maple Grove, Minneapolis, MN, USA), shunts the aqueous humor directly to the ocular surface, implanted through an ab externo approach, theoretically providing an advantage to glaucoma patients suffering also from dry eye syndrome, although possibly raising the issue of long-term infections. This device is still undergoing preliminary trials to examine its safety and efficacy. Other devices combine elements of both classic filtration surgery and MIGS. One such device, the minimally invasive microsclerectomy (Sanoculis, Kiryat Ono, Israel) device, uses an ab interno approach to perform a sclerocorneal drainage channel resembling that of trabeculectomy. Last, renewed interest has been shown lately in the ExTra Laser System (ExTra ELT; MLase AG, Germering, Germany), which received a CE mark in 2014. This treatment uses a 308-nm xeon chloride excimer laser to create openings through the TM and inner Schlemm canal. It was shown to be effective in patients with POAG refractory to medical treatment and has shown good results comparable to those of SLT, with the advantage of being combined with phacoemulsification [
      • Babighian S.
      • et al.
      Excimer laser trabeculotomy vs 180 degrees selective laser trabeculoplasty in primary open-angle glaucoma. A 2-year randomized, controlled trial.
      ].

      Summary

      The question of which glaucoma procedure best fits which patient has been complicated recently by the enlarging advances of new glaucoma devices and techniques, which have on one hand enriched our possibilities for intervention, but on the other hand have produced the need for much more quality research to examine their efficacy. Although in the past, the choice to surgically intervene would mean opting for either a classic filtration surgery, such as trabeculectomy, or a tube shunt when refractory to medical treatment, nowadays intervening at an early level is recommended by many to control other factors, such as medication burden, compliance, and quality of life.
      The decision of which treatment to choose should be dictated in part by the type of the disease, level of the disease, preoperative and target pressures, ocular status, different patient parameters, and surgeon preference.
      It is reasonable to classify glaucoma interventions according to the route of targeted treatment into the following: subconjunctival, Schlemm canal–based, and suprachoroidal procedures, as this might give a better indication of the level of efficacy achieved by each approach.
      The choice of the subconjunctival route should be made when in need of a lower target pressure, in advanced disease, or when past angle-based surgery has failed to provide the required target. Although trabeculectomy can be chosen when in the need of a single-digit target pressure, other interventions, such as the Xen, and the Preserflo implants might provide similar or slightly reduced efficacy in exchange for a faster surgery, better safety profile, and faster recovery, yet awaiting results from head-to-head RCTs. DS might give good results comparable to those of trabeculectomy, with a safer postoperative course. Tube shunts, on the other hand, should be reserved mainly for patients with failed subconjunctival surgery, conjunctival scarring, and secondary complex glaucoma cases precluding the option for other procedures in the category.
      Cyclodestructive procedures are usually indicated in patients with low visual potential refractory to medical or surgical treatment, but the addition of micropulse laser treatment to the arsenal has raised the possibility of earlier treatment owing to the higher safety profile compared with continuous-wave TSCPC. Endocyclophotocoagulation is another ab interno approach to cilioablation that awaits further validation in future studies.
      Schlemm canal–based procedures are more suitable for patients with mild to moderate glaucoma and concomitant cataract, in need of more control of their IOP or medications. It might also be considered in patients who have failed prior incisional surgery, unwilling or at risk of serious complications undergoing additional surgery.
      The suprachoroidal space is yet to be studied more to provide answers to fibrosis issues, and some promising devices are on the way, while others have failed because of safety or efficacy issues.
      Patients with PAC or PACG might benefit from early cataract surgery, as it might be a more permanent solution to their IOP and improve significantly their angle parameters. Additional interventions, such as GSL, should be considered strongly, especially when a significant amount of residual PAS is remaining at the end of the cataract surgery. The addition of an MIGS procedure when visualization of the angle is rendered feasible, might have an added benefit in these cases.
      Patients with NVG are usually more refractory to treatment and entail the choice of a tube shunt, preferably with a valved mechanism or ligated tube in a nonvalved shunt to provide an immediate reduction of IOP with less risk of hypotony and choroidal effusion in view of the very high IOPs usually present. Cyclodestructive procedures are to be strongly considered when the visual potential is very low, although micropulse laser treatment also should be considered in patients with good visual acuity.
      In conclusion, the increasingly enlarging treatment arsenal for glaucoma has fortified our capabilities of defying this chronic disease and makes us wait for more data on their use and anticipate with eagerness further innovations and scientific breakthroughs in the field.

      Clinics care points

      • In patients requiring low target pressure postoperatively, one should opt for subconjunctival surgery.
      • Avoid doing Schlemm canal–based procedures, especially excisional procedures, in patients who perform Valsalva or those with high episcleral venous pressure.
      • One must make all efforts to prevent hypotony in patients undergoing subconjunctival surgery, especially in older patients with very high preoperative pressures and advanced disease.

      Disclosure

      R. Kassem has nothing to disclose. P. Harasymowycz has the following disclosures: Allergan: B) Consultant and D) Research. Alcon B) Consultant. Bausch Health A) Consultant, B) Consultant, and D) Research. Novartis B) Consultant. Glaukos A) Consultant, B) Consultant, and D) Research. Ivantis A) Consultant, B) Consultant, and D) Research. Thea B) Consultant and D) Research. Santen B) Consultant. Iridex-Salient Medical B) Consultant. New World Medical–Labtician B) Consultant. Johnson & Johnson Vision A) Consultant, B) Consultant and D) Research. Zeiss P) Product. Aequus B) Consultant. Aerie D) Research.

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