top of page
OAn Update on Surgical Glaucoma Options and
a Look Towards the Future  
​

By Yusuf Ahmed, MD, Jamie Beckman, DO, and Irfan N. Kherani, MD, FRCSC

adobe-pdf-icon.png

Click to download a PDF version of this article

This issue of Ophthalmology Rounds aims to provide an up-to-date synthesis of the current surgical options for glaucoma management, highlighting newer techniques and novel devices. By summarizing the indications, mechanisms, efficacy, and safety profiles of common (non-exhaustive) options, this article seeks to equip ophthalmologists with a greater understanding of the evolving surgical landscape and highlight innovations that may shape the future of glaucoma care.

 

Glaucoma is one of the leading causes of irreversible vision loss, with a projected global prevalence of approximately 111.8 million people affected by 2040.¹ The treatment of glaucoma has historically followed an algorithm of first using topical anti-glaucoma medications (AGMs), followed by lasers, and lastly invasive filtering surgery. Given the high morbidity associated with AGMs and traditional filtering surgery,² several newer surgical techniques and devices have been developed that offer reductions in intraocular pressure (IOP) with differing risk profiles (Table 1).³ Trabeculectomy remains the gold standard for achieving significant IOP and AGM reduction;⁴ however, since the introduction of glaucoma drainage devices (GDDs), the volume of trabeculectomies has declined and the number of GDDs and tube shunts have increased by >200%.⁵⁻⁶ Minimally invasive glaucoma surgeries (MIGS) have similarly gained rapid momentum.⁵⁻⁶ MIGS now represent nearly 50% of glaucoma interventions performed in patients with mild-to-moderate disease at the time of cataract surgery (CS).⁶ While these newer procedures are generally safe, they offer only modest reductions in IOP and AGM.⁷

Table 1. Summary of current surgical glaucoma devices and techniques

FDA = Food and Drug Administration; CE = Conformité Européenne; HC = Health Canada; KDB = Kahook Dual Blade; BANG = bent ab interno needle goniotomy; GATT = gonioscopy-assisted transluminal trabeculotomy; ECP = endocyclophotocoagulation; ECPL = endocyclophotocoaguloplasty; ELT = Excimer Laser Trabeculotomy; AB-MIGS = angle-based minimally-invasive glaucoma surgery; S-MIGS = supraciliary MIGS; MIBS = minimally-invasive bleb surgery

Interventional Glaucoma (IG)​

​

The expansion of safer, efficacious surgical options has catalyzed a shift towards an IG mindset.⁸ The Early Manifest Glaucoma Trial demonstrated that 45% of eyes treated with laser and topical medications still experienced glaucoma progression.⁹ IG challenges the traditional stepwise paradigm of medications followed by lasers and lastly surgery, emphasizing earlier, individualized intervention rather than reserving surgery solely for advanced disease requiring large IOP reduction. With a broader armamentarium of devices and techniques, surgeons can now incorporate patient preferences, such as the desire to reduce medication burden, and tailor the target IOP to the specific clinical scenario. Early surgical intervention may be associated with a reduced rate of glaucomatous progression, even when taking into account IOP reduction.¹⁰

 

Importantly, IG should not be interpreted as synonymous with surgery alone; rather, it represents a philosophy that supports the judicious and personalized use of IOP-lowering therapies to prevent glaucomatous progression and disease-related morbidity. While AGMs and trabeculectomy remain essential components of glaucoma care, less invasive and safer surgeries can offer meaningful benefits for appropriately selected patients. 

 

Angle-Based (AB) MIGS

​

AB-MIGS, often performed ab interno alongside CS, has become increasingly popular for patients with open-angle glaucoma (OAG) desiring mild-to-modest IOP reduction. AB-MIGS is particularly effective in patients with primary trabecular meshwork (TM) dysfunction and secondary OAGs like pseudoexfoliation and pigment dispersion glaucoma. Hyphema and IOP spike are the most common adverse events. Neither event is typically of significant long-term consequence.¹¹ 

 

Excisional goniotomy 

​

Excisional goniotomy modalities aim to remove TM to enhance access to the outer Schlemm’s canal (SC), collector channels, and the distal outflow system. 

 

The Kahook Dual Blade® (KDB; New World Medical) is a handheld stainless-steel device with a footplate incorporating a pointed tip, ramp, and dual-edged blade. Under gonioscopy, the blade tip engages the TM, the ramp elevates the tissue, and the blade excises TM as it is advanced 3–5 clock hours.¹² A systematic review reported IOP reductions of 11%–36% for stand-alone KDB and 11%–34% for phaco-KDB.¹² Hyphema and IOP spike may occur in the early postoperative period but are transient and rarely have long-term effect.¹²⁻¹³ 

 

The Trabectome® (Neomedix Corp.) uses plasma-mediated ablation with a bipolar 550 kHz tip to remove 30°–90° of TM. Prospective data from 37 eyes with OAG demonstrated IOP reduction from 28.2 mmHg (on 1.2 AGMs) to 17.4 mmHg (on 0.4 AGMs) at 6 months.¹⁴ A meta-analysis reported mean IOP reductions of 9.77 mmHg for Trabectome only and 6.04 mmHg for phaco-Trabectome, with decreased AGM in both groups; the Trabectome-only pooled cohort had higher baseline IOP, likely explaining the greater reduction.¹⁵ 

 

Bent-needle ab interno goniotomy (BANG) offers a low-cost readily available alternative to excisional MIGS; all that is required is a 25-gauge needle, bent at the distal 1-mm end towards the bevel to create a goniotome.¹⁶ Approximately 100° of TM can be excised. In the seminal BANG study, 73% of patients with OAG achieved ≥20% IOP reduction and were medication-free at 6 months.¹⁶ BANG demonstrates a similarly low rate of serious adverse events compared to other methods of excisional goniotomy.¹⁷ 

 

Incisional goniotomy 

​

Incisional goniotomy MIGS opens the TM to permit greater access to SC and distal collector channels, leaving leaflets of tissue overlying SC.¹⁸

 

Gonioscopy-assisted transluminal trabeculotomy (GATT) is an ab interno MIGS designed to restore physiologic aqueous outflow by circumferentially unroofing SC. After creation of a goniotomy, a 5-0 or 6-0 polypropylene suture is advanced 180–360° through SC using micro-forceps (Figure 1). The suture is then pulled through, creating a complete or hemi-circumferential trabeculotomy. GATT is cost-effective, requiring only a suture and gonioprism. In the initial multi-surgeon series of 198 eyes with OAG, 360° GATT ± CS significantly reduced IOP by 37.3% (-9.2 mmHg) and decreased AGMs by 1.43 at 24 months.¹⁹ A large meta-analysis showed that phaco-GATT achieved greater IOP reduction compared to non-GATT goniotomies and TM-bypass MIGS.11 Transient hyphema (27.7%) and IOP spikes (8.7%) were the most common complications. Superior and inferior hemi-GATT may provide similar IOP reduction and hyphema rates.²⁰⁻²¹ Literature comparing hemi- and 360° GATT yields mixed results;²¹⁻²³ however, stronger prospective analyses appear to demonstrate similar efficacy with higher rate of hyphema in 360° GATT compared to inferior hemi-GATT.²¹⁺²³

Figure 1. 5-0 Prolene suture fed into SC under direct gonioscopic view.

Figure 1x web.jpg

The Tanito Microhook (mLOT) (Inami & Co., Ltd.) is a TM-incising system marketed to achieve greater degrees of trabeculotomy compared to other devices through use of 3 specially designed microhooks: straight, right-angled, and left-angled. A randomized, controlled trial (RCT) comparing stand-alone phacoemulsification to combined phaco-mLOT in mild-to-moderate primary open-angle glaucoma (POAG) eyes found that mLOT achieved significantly greater IOP and AGM reductions at 1 year, with 90.3% of patients achieving study-defined complete success.²⁴ Hyphema was the main adverse event (~7% of eyes).

 

The TrabExTM, TrabEx+TM, and TrabEx ProTM (MicroSurgical Technology) are irrigating goniotomy modalities that use a serrated dual blade to incise TM and remove tissue. An attached irrigation system allows for good visualization of the angle, clearing hyphema and maintaining the AC. One study of 73 eyes with POAG demonstrated 34% IOP reduction and decrease in AGM (2.9 to 1.9) at an intermediate timepoint.²⁵ Hyphema and IOP spike occurred in 17% and 4% of patients, respectively. 

 

The SION® Surgical Instrument (Sight Sciences, Inc.) is a bladeless TM-incising device with some excising capabilities.²⁶ As the device tip engages the TM, the lower foot of the tip punctures the TM while the upper foot facilitates the TM into a collection trap. There is limited literature evaluating this device. In a study demonstrating ease of use among residents, 38 eyes undergoing phaco-SION experienced a mean IOP reduction of 2.1 mmHg and 0.4 AGMs at 3 months.²⁷ IOP spike (13%) and hyphema (16%) occurred within typical AB-MIGS range.

 

Tissue-sparing canaloplasty 

​

Canaloplasty functions analogously to angioplasty: circumferential catheterization opens partially obstructed regions of SC, while viscodilation enhances flow through distal collector channels. Canaloplasty devices are meant to be a tissue-sparing procedure but are often performed in combination with trabeculotomy.

 

The iTrack™ and iTrack™ Advance (Nova Eye) use an illuminated fibreoptic microcatheter to complete 360° ab interno canaloplasty (ABiC), or less commonly ab externo canal catheterization, with controlled viscodilation. After a small goniotomy is created and the microcatheter is advanced circumferentially, the catheter is retracted and small aliquots of pressurized ophthalmic viscosurgical device (OVD) are delivered into SC and the distal outflow system. The iTrack™ Advance integrates a 220-µm microcatheter with an ergonomic handpiece enabling catheterization, viscodilation, and goniotomy using a single device. Multiple studies have demonstrated meaningful IOP and medication reductions in mild-to-moderate, and potentially severe, OAG with low risk of significant adverse events.²⁸⁻²⁹

 

The OMNI® Surgical System handpiece contains a microcatheter deployment system, OVD reservoir, and injection port. After the bevelled tip of the handpiece is used to create a goniotomy, the microcatheter is advanced 180° while OVD viscodilates SC. Two passes are required to achieve full 360° effect. A second advancement and subsequent withdrawal can be performed to cleave 180° of TM. Studies of stand-alone and phaco-OMNI® insertion demonstrate significant IOP and medication reductions with a strong safety profile.³⁰⁻³¹ 

 

Trabecular bypass and/or stenting

​

The iStent® Trabecular Micro-Bypass System (Glaukos) enhances aqueous outflow with permanently stented channels through the TM into SC.³² The original iStent G1 is an L-shaped, heparin-coated titanium implant measuring 1.0x0.3 mm. Newer injectable models contain multiple preloaded injectable iStents with side-flow outlets permitting for multidirectional flow into SC. iStent Inject (G2) combined with CS provides greater unmedicated IOP reduction at 24 months (-7.0 mmHg vs -5.4 mmHg; P<0.001) and higher rates of ≥20% IOP reduction (75.8% vs 61.9%; P=0.005) compared to CS alone in mild-to-moderate POAG eyes.³³ Complications are uncommon and comparable to phacoemulsification alone.³³ 

 

The Hydrus® Microstent (HMS; Alcon) is an 8-mm, nitinol, crescent-shaped intracanalicular scaffold spanning 90° of SC with a 290-µm inlet and 3 outflow windows, designed to maintain canal patency and enhance TM bypass. The HMS is meant to be inserted into the nasal angle until the intracanalicular scaffold spans 3 clock hours. The HORIZON RCT demonstrated sustained IOP lowering at 5 years; CS+HMS outperformed CS alone, with more eyes achieving IOP ≤18 mmHg (49.5% vs 33.8%; P=0.003) and ≥20% IOP reduction without AGMs (54.2% vs 32.8%; P<0.001).³⁴ Peripheral anterior synechiae formation was increased in the HMS group vs CS alone, but other complications were similar.³⁴ HORIZON also showed that HMS+CS had a significantly decreased rate of visual field progression in fast glaucoma progressors compared to CS alone.¹⁰

 

Laser-angle surgery

​

Endocyclophotocoagulation (ECP), first reported in 1992, is a cyclodestructive minimally invasive laser procedure that uses an endoscope to visualize and laser the ciliary processes.³⁵ A 810-nm semiconductor diode helium laser causes shrinkage and ablation of the ciliary processes, reducing aqueous production. ECP is more precise compared to transscleral cyclophotocoagulation (tsCPC) and results in less overall tissue disruption.³⁶⁺³⁷ Compared to tsCPC, ECP causes less hypotony, phthisis bulbi, sympathetic ophthalmia, and necrotizing scleritis.³⁸ ECP is now being used in eyes with good visual potential, with studies showing greater IOP lowering in combined phaco-ECP versus phacoemulsification alone.³⁹⁺⁴⁰

 

Endocyclophotocoaguloplasty (ECPL) differs from ECP in that energy is applied to the posterior ciliary processes, mechanically rotating the processes to open the angle while contributing some aqueous production reduction.⁴¹ ECPL is particularly effective in plateau iris. When combined with CS, ECPL may be as effective as phaco-trabeculectomy in reducing IOP and AGMs in patients with primary angle closure (± glaucoma), with fewer adverse events.⁴²

 

Excimer laser trabeculostomy (ELT) is an implant-free MIGS that applies a ‘cold’ 308-nm xenon chloride excimer laser through fibreoptic cable to photoablate the TM.⁴³ The laser creates 10 microchannels (210 µm diameter) over 90°. Viscocanalostomy occurs during each microchannel creation as gas from ablated tissues passes through adjacent trabeculostomies and collector channels, further augmenting aqueous outflow.⁴³ A meta-analysis found that ELT±CS achieved a 3-10-mmHg reduction of IOP and 1.8 decrease in AGMs,⁴⁴ and another systematic review describes a 20%–40% IOP reduction after ELT±CS.⁴⁵ Compared to laser trabeculopuncture,⁴⁶ ELT does not cause significant thermal damage to surrounding tissue, thereby maintaining the outflow system and reducing fibrosis. Consequently, ELT may offer sustained IOP-lowering effect 8 years after procedure.⁴⁷ Reported complications of hyphema and IOP spike are transient and uncommon.⁴⁵⁺⁴⁶

 

Supraciliary MIGS (S-MIGS)

​

Supraciliary devices are an emerging category of MIGS, inspired by the original cyclodialysis operation first introduced in 1905 by Leopold Heine.⁴⁸ Due to its large surface area and negative pressure gradient, the suprachoroidal space is a promising area of target to lower IOP.⁴⁹⁺⁵⁰ Compared to AB-MIGS, the “landing zone” of the uveoscleral space is larger, potentially allowing for more forgiving insertion. 

 

The MINIject™ Implant (iSTAR Medical) is a silicone–based microporous device containing 200 000 interconnected hollow spheres that allow aqueous to percolate into the suprachoroidal space.⁵¹ After insertion between scleral spur and ciliary body, the implant biointegrates into the eye, thought to allow for sustained long-term efficacy and reduced fibrosis. The STAR trials evaluated the MINIject as a standalone procedure in 82 patients with mild-to-moderate OAG.⁵² Mean medicated diurnal IOP was reduced by 39.3% (23.8 mmHg to 14.4 mmHg; P<0.0001) at 2 years, AGMs were reduced significantly with 37.9% of patients medication-free, and minimal endothelial cell loss (ECL) at 2 years (6.2%).

 

The AlloFlo™ Uveo (Iantrek, Inc) is a similar bio­interventional supraciliary scaffold made from a micro­trephined scleral allograft designed to create a durable uveoscleral outflow conduit without permanent synthetic hardware.⁵³ A scleral allograft (5 mm length x 500 µm width) is prepared from donor sclera. After creation of a cyclodialysis cleft and injection of cohesive OVD to expand the uveoscleral system, the scaffold is inserted 5 mm into the endoscleral space above the ciliary body. The 2-year CREST trial of 31 patients with POAG undergoing combined phacoemulsification with AlloFlo implantation showed that 74% of eyes achieved a ≥20% IOP reduction, with mean IOP decreasing from 21.9 mmHg on 1.22 AGMs to 13.8 mmHg on 0.5 AGMs.⁵⁴ Adverse events were uncommon and transient, and ECL was comparable to expected changes after phaco‑emulsification. 

 

Minimally Invasive Bleb Surgery (MIBS)

​

MIBS is a less invasive filtering surgery indicated for moderate-to-severe glaucoma that creates a subconjunctival bleb using small shunts or tubes to reduce IOP.⁵⁵ 

 

The Xen® Gel Stent (AbbVie Inc.) is a 6-mm-long cylindrical implant made of cross-linked collagen from porcine gelatin.⁵⁶ The Xen Gel Stent offers 45µm and 63µm lumen diameters and can be inserted ab interno with an injector or ab externo with open conjunctival dissection. The Xen 63 achieved slightly lower postoperative IOP (9.1-12.7 mmHg) compared to the Xen 45 (10.2-15.5 mmHg), with fewer AGMs in the 63 group (0.6 vs 1.7).⁵⁶⁺⁵⁷ Higher complete success rate was also achieved with the Xen 63. Both studies showed higher adverse events in the Xen 63 stent, mostly from postoperative hypotony which was transient and resolved.

 

The PreserFlo™ Microshunt (Glaukos) is a bleb-forming microshunt made of polystyrene-isobutylene-styrene (SIBS) material that is 8.5 mm in length with a 70-µm lumen. The microshunt is divided into 2 parts, a 4.5-mm proximal and 3-mm distal end, separated by a 1-mm fin. The SIBS material has excellent biocompatibility, resulting in minimal inflammation, decreasing capsular tissue formation, and conjunctival scarring.⁵⁸ In a meta-analysis, the PreserFlo Microshunt significantly reduced IOP by 41.5% (-8.9 mmHg) and reduced AGMs by 2.7.⁵⁹ It has a favourable safety profile, including reduced risk of postoperative hypotony maculopathy compared to the traditional trabeculectomy due to the small lumen and posterior bleb formation.⁵⁹ Aqueous outflow can be titrated to reduce risk of hypotony with a 9-0 or 10-0 nylon or polypropylene intraluminal suture.⁶⁰ 

 

Novel Glaucoma Drainage Devices (GDDs)

​

A tube shunt is a small surgical implant consisting of a flexible tube and a plate that drains aqueous humor to an external reservoir. Patients typically experience IOP in the mid-teens and often require AGMs after surgery. Tube shunts can be valved or nonvalved. The only currently available valved implant is the Ahmed® Glaucoma Valve (AGV; New World Medical), which consists of a venturi shaped chamber on the plate that utilizes Bernoulli’s principle.⁶¹ The valve opens at 8 mmHg to drain aqueous humor to allow for immediate drainage without the need for secondary ligatures to decrease the risk of postoperative hypotony.

 

Newer nonvalved glaucoma tube shunts include the Ahmed® Clearpath (ACP) implant (New World Medical), which offers 250-mm² and 350-mm² plate sizes with an internal lumen diameter of 0.305 mm but has increased flexibility, a lower plate profile, and a preloaded poly­propylene ripcord vs earlier devices.⁶² A similar IOP-lowering effect with lower postoperative AGM use was found in eyes treated with ACP 250 mm² and 350 mm² compared to eyes treated with Baerveldt® (Johnson & Johnson Vision) 250-mm² and 350-mm² glaucoma drainage devices; however, plate size was not controlled between devices.⁶³ A retrospective series of 104 eyes found that 250 mm² and 350 mm² plate sizes produced similar IOP lowering with more diplopia in the larger plate group; early hypotony occurred in 6.7% of patients.⁶⁴ 

 

The Ahmed® Clearpath ST (New World Medical) is a new iteration of the ACP that also has a 250-mm² or 350-mm² plate size option, but most notably a tube with an internal lumen size of 0.127mm.⁶² Theoretical improved safety and decreased postoperative complications vs larger-lumen tube shunts have not been confirmed by comparative studies.

 

The PAUL® Glaucoma Implant (PGI, Advanced Ophthalmic Innovations) is a 342-mm² silicone plate with an internal tube diameter of 0.127 mm that is implanted below the recti muscles.65 Like the Clearpath ST, the PAUL implant has a smaller internal lumen diameter that theoretically should decrease the risk for postoperative hypotony; however, 1 study showed numerically fewer early and late postoperative complications compared to the Baerveldt implant and another showed no difference.65 Interestingly, up to 94% of eyes undergoing PAUL implantation have shown a double-layered bleb morphology, which correlated with lower IOP values.⁶⁵ 

 

Looking to the Future

​

Next-generation implants and procedures are focused on maintaining good IOP lowering while reducing the rates of complications such as hypotony and bleb encapsulation through biointegratable materials, innovative design, and/or unique components.

 

The GORE GDI (W.L. Gore & Associates) is a novel, low-profile implant consisting of a bilayered expanded polytetrafluoroethylene (ePTFA) membrane and silicone tube. ePTFA offers a more biocompatible, microporous polymer compared to current tube shunts that is hypothesized to reduce bleb encapsulation.⁶⁶ The VisiPlate® (Avisi Technologies Inc.) is an ultra-thin (30 µm) GDI measuring 5 mm x 9 mm made of aluminum oxide plate coated with biocompatible parylene-C. The plate contains multiple fenestrations that aim to control and shunt aqueous more diffusely and reduce the rate of hypotony. Interim results of a pilot study (15 patients with OAG) found a 40% IOP reduction to 14.0 mmHg and AGM reduction from 2.0 to 0.8 at 6 months.⁶⁷ There were no reported choroidal effusions requiring surgical intervention.

 

The Calibreye™ Titratable Glaucoma Surgical System (Myra Vision, Inc) is a developmental filtration device made of nitinol and silicone that features 3 titratable flow channels connecting the AC with the subconjunctival space.⁶⁸ Two channels can be opened and closed using a transcorneal green laser, allowing for 4 different aqueous outflow settings. Studies in rabbits have demonstrated good tolerability with ability of the laser to open and close the valves.

 

The Femtosecond Laser Image-Guided High-Precision Trabeculotomy (FLIGHT) is a novel noninvasive laser-angle procedure that uses a femtosecond laser to create a 500 µm x 200 µm channel through the TM. FLIGHT is performed without corneal incision, reducing associated risk. The initial 2-year nonrandomized prospective study evaluating the ViaLase® Laser System (ViaLase Inc) in 18 eyes with OAG demonstrated IOP reduction from 22.3 mmHg to 14.5 mmHg (82.3% eyes achieving >20% reduction) without a significant decrease in AGMs at 24-month follow-up.⁶⁹ FLIGHT channels were prominently visible at the latest follow up, indicating good patency and outflow. There were no cases of hyphema or IOP spike.

 

Conclusion

​

Newer devices and surgical approaches with good IOP-lowering efficacy can now bridge the gap between drop/laser management and trabeculectomy. Surgery may now be considered earlier for patients with mild, moderate, or advanced glaucoma, especially in those with concurrent cataract. 

 

Often combined with CS, AB-MIGS and S-MIGS are lower on the risk profile, but also less likely to eliminate AGM. Higher on the risk-benefit spectrum are S-MIGS that utilize the potential suprachoroidal space. Further escalating risk and reward, MIBS and novel GDDs create a new drainage channel into the subconjunctival and/or subtenon space creating a predictable posterior bleb. Trabeculectomy remains the gold standard for individuals requiring the greatest possible IOP reduction; however, with an evolving landscape of surgical options, we can deliver more precise care to patients in a relatively safe manner, while factoring in preferences and specific IOP target ranges.

 

Affiliations:

​

Dr. Ahmed is a resident physician, Department of Ophthalmology and Vision Sciences, University of Toronto, Toronto, Ontario.

Dr. Beckman is a glaucoma and advanced anterior segment surgeon at EyeCare Partners, Dearborn, Michigan, and is Adjunct Faculty at John A. Moran Eye Center, University of Utah, Salt Lake City, Utah.

Dr. Kherani is an Assistant Professor, Department of Ophthalmology and Vision Sciences, University of Toronto, Toronto, Ontario.

 

Disclosures

​

Drs. Ahmed and Beckman stated that they have no disclosures to report in association with the contents of this article.

Dr. Kherani has received lecture and/or consultant fees from AbbVie, Aequus Pharmaceuticals, Alcon Canada, Bausch + Lomb, Glaukos, Labtician Ophthalmics, Sophia Labs, Théa Pharma Canada, and Zeiss Canada, and he has received study support from Alcon Canada, Bausch + Lomb, Glaukos, Johnson & Johnson, and Théa Pharma Canada.

​

References

​

  1. Tham YC, Li X, Wong TY, Quigley HA, Aung T, Cheng CY. Global prevalence of glaucoma and projections of glaucoma burden through 2040: a systematic review and meta-analysis. Ophthalmology. 2014;121(11):2081–2090. 

  2. Peixoto RDS, Stringa F, Cammack R, Liput J, King AJ. Emerging perspectives in quality of life after trabeculectomy surgery. Eye (Lond). 2025;39(7):1394–1399. 

  3. Micheletti JM, Shultz M, Singh IP, Samuelson TW. An emerging multi-mechanism and multi-modal approach in interventional glaucoma therapy. Ophthalmol Ther. 2025;14(1):13–22. 

  4. Musch DC, Lichter PR, Guire KE, Standardi CL. The Collaborative Initial Glaucoma Treatment Study: study design, methods, and baseline characteristics of enrolled patients. Ophthalmology. 1999;106(4):653–662. 

  5. Arora KS, Robin AL, Corcoran KJ, Corcoran SL, Ramulu PY. Use of various glaucoma surgeries and procedures in Medicare beneficiaries from 1994 to 2012. Ophthalmology. 2015;122(8):1615–1624.

  6. Vinod K, Gedde SJ, Feuer WJ, et al. Practice preferences for glaucoma surgery: a survey of the American Glaucoma Society. J Glaucoma. 2017;26(8):687–693.

  7. Bidiwala S, Fatehi N, Singh M, et al. Outcomes of minimally invasive glaucoma surgery (MIGS): impact on intraocular pressure, medication use, and need for secondary surgery – a 3-year real-world cohort study. J Glaucoma. 2025;34(1):e45–e53.

  8. Funke C, Ristvedt D, Yadgarov A, Micheletti J. Interventional glaucoma consensus treatment protocol. Expert Rev Ophthalmol. 2025;20(2):79–87.

  9. Heijl A, Leske MC, Bengtsson B, et al. Reduction of intraocular pressure and glaucoma progression: results from the Early Manifest Glaucoma Trial. Arch Ophthalmol. 2002;120(10):1268–1279.

  10. Montesano G, Ometto G, Ahmed IIK, et al. Five-year visual field outcomes of the HORIZON trial. Am J Ophthalmol. 2023;251:143–155. 

  11. Yuan PHS, Dorling M, Shah M, Panarelli JF, Durr GM. Combined microinvasive glaucoma surgery with phacoemulsification in open-angle glaucoma: a systematic review and meta-analysis. Am J Ophthalmol. 2025;270:154–163.

  12. Dorairaj S, Radcliffe NM, Grover DS, et al. A review of excisional goniotomy performed with the Kahook Dual Blade for glaucoma management. J Curr Glaucoma Pract. 2022;16(1):59–64.

  13. Radwan L, El Jalbout JD, Trad K, et al. Outcomes of phacoemulsification with or without Kahook Dual Blade Goniotomy for glaucoma patients with cataract. J Glaucoma. 2024;33(10):769–779. 

  14. Minckler DS, Baerveldt G, Alfaro MR, Francis BA. Clinical results with the Trabectome for treatment of open-angle glaucoma. Ophthalmology. 2005; 112(6):962–967. 

  15. Kaplowitz K, Bussel II, Honkanen R, et al. Review and meta-analysis of ab-interno trabeculectomy outcomes. Br J Ophthalmol. 2016;100(5):594–600.

  16. Shute T, Green W, Liu J, Sheybani A. An alternate technique for goniotomy: description of procedure and preliminary results. J Ophthalmic Vis Res. 2022; 17(2):170–175. 

  17. Ayub G, Costa VP. Bent Ab interno needle goniotomy versus gonioscopy­assisted transluminal trabeculotomy in primary open angle glaucoma: a randomized clinical trial. J Glaucoma. 2025;34(11):924–932.

  18. Ammar DA, Seibold LK, Kahook MY. Preclinical investigation of goniotomy using four different techniques. Clin Ophthalmol. 2020;14:3519–3525. 

  19. Grover DS, Godfrey DG, Smith O, Feuer WJ, Montes de Oca I, Fellman RL. Gonioscopy-assisted transluminal trabeculotomy, ab interno trabeculotomy: technique report and preliminary results. Ophthalmology. 2014;121(4):855–861. 

  20. Waldner DM, Chaban Y, Penny MD, et al. Segmental suture gonioscopy-assisted transluminal trabeculotomy: comparison of superior versus inferior hemisphere outcomes. J Glaucoma. 2023;32(5):396–406.

  21. Sato T, Kawaji T. 12-month randomised trial of 360° and 180° Schlemm’s canal incisions in suture trabeculotomy ab interno for open-angle glaucoma. Br J Ophthalmol. 2021;105(8):1094–1098.

  22. Matlov Kormas R, Gafni Klepfish E, Marcovich A, Kassem R. Efficacy and safety of 360º and 180º gonioscopy-assisted transluminal trabeculotomy in combination with phacoemulsification in patients with open-angle glaucoma: a retrospective case-control study. BMC Ophthalmol. 2025;25(1):656. 

  23. Gunay M, Cigiltepe IB, Turk A, Uzlu D, Kose B. A prospective comparison of 180 versus 360-degree gonioscopy-assisted transluminal trabeculotomy outcomes in pseudoexfoliation glaucoma. J Glaucoma. 2024;33(8):559–565.

  24. Maheshwari D, Grover DS, Ramakrishnan R, Pillai MR, Chautani D, Kader MA. Early outcomes of combined phacoemulsification and ab interno Tanito Microhook Trabeculotomy in open-angle glaucoma. Ophthalmol Glaucoma. 2024;7(2):123–130. 

  25. Gosling D, Wang H, Auger G. Early results of irrigating goniectomy with TrabEx+: a novel device for the treatment of open-angle glaucoma. J Glaucoma. 2022; 31(4):268–273. 

  26. Ammar DA, Porteous E, Kahook MY. Preclinical investigation of ab interno goniotomy using three different techniques. Clin Ophthalmol. 2023;17:2619–2623. 

  27. Mokhashi N, Patterson I, Qiu M. Safety and efficacy of resident-performed SION goniotomy at the time of cataract surgery. Invest Ophthalmol Vis Sci. 2024;65(7):3471.

  28. Gallardo MJ. 36-month effectiveness of ab-interno canaloplasty standalone versus combined with cataract surgery for the treatment of open-angle glaucoma. Ophthalmol Glaucoma. 2022;5(5):476–482.

  29. Patel S, Reiss G. Long-term clinical and safety outcomes of canaloplasty performed across all grades of glaucoma severity. J Ophthalmol. 2023 10;2023:5625990.

  30. Vold S, Williamson B, Hirsch L, et al. Canaloplasty and trabeculotomy with the OMNI system in pseudophakic patients with open-angle glaucoma: the ROMEO study. Ophthalmol Glaucoma. 2021;4(2):173–181. 

  31. Greenwood MD, Yadgarov A, Flowers BE, Sarkisian SR Jr, Ohene-Nyako A, Dickerson JE Jr; GEMINI 2 Study Group. 36-Month outcomes from the prospective GEMINI study: canaloplasty and trabeculotomy combined with cataract surgery for patients with primary open-angle glaucoma. Clin Ophthalmol. 2023;17:3817–3824. 

  32. Le K, Saheb H. iStent trabecular micro-bypass stent for open-angle glaucoma. Clin Ophthalmol. 2014;8:1937–1945. 

  33. Samuelson TW, Sarkisian SR Jr, Lubeck DM, 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. Ophthalmology. 2019; 126(6):811–821. 

  34. Ahmed IIK, De Francesco T, Rhee D, et al. Long-term outcomes from the HORIZON randomized trial for a Schlemm’s canal microstent in combination cataract and glaucoma surgery. Ophthalmology. 2022;129(7):742–751. 

  35. Uram M. Ophthalmic laser microendoscope ciliary process ablation in the management of neovascular glaucoma. Ophthalmology. 1992;99(12):1823–1828.

  36. Pantcheva MB, Kahook MK, Schuman JS, Noecker RJ. Comparison of acute structural and histopathological changes in human autopsy eyes after endoscopic cyclophotocoagulation and trans-scleral cyclophotocoagulation. Br J Ophthalmol. 2007; 91(2):248–252

  37. Lin SC, Chen MJ, Lin MS, Howes E, Stamper RL. Vascular effects of ciliary tissue from endoscopic versus trans-scleral cyclophotocoagulation. Br J Ophthalmol. 2006;90(4):496–500.

  38. Noecker RJ. Complications of endoscopic cyclophotocoagulation: ECP Collaborative Study Group. Paper presented at The ASCRS Symposium on Cataract, IOL and Refractive Surgery. San Diego CA; May 1, 2007. 

  39. Francis BA, Berke SJ, Dustin L, Noecker R. Endoscopic cyclophotocoagulation combined with phacoemulsification versus phacoemulsification alone in medically controlled glaucoma. J Cataract Refract Surg. 2014;40(8):1313–1321. 

  40. Siegel MJ, Boling WS, Faridi OS, et al. Combined endoscopic cyclophotocoagulation and phacoemulsification versus phacoemulsification alone in the treatment of mild to moderate glaucoma. Clin Exp Ophthalmol. 2015;43(6):531–539. 

  41. Francis BA, Pouw A, Jenkins D, et al. Endoscopic cycloplasty (ECPL) and lens extraction in the treatment of severe plateau iris syndrome. J Glaucoma. 2016; 25(3):e128–133. 

  42. Pathak-Ray V, Choudhari N. Phaco-endocycloplasty versus phacotrabeculectomy in primary angle-closure glaucoma: a prospective randomized study. Ophthalmol Glaucoma. 2020;3(6):434–442. 

  43. Berlin MS. Rajachich G, Duffy M, Grundfest W, Goldenbert T. Excimer laser photoablation in glaucoma filtering surgery. Am J Ophthalmol. 1987;103(5):713–714.

  44. Toeteberg-Harms M, Stevenson S. AGS 2025: Long-term efficacy and safety of standalone and phaco ELT. Ophthalmology Times. February 27, 2025. 

  45. Durr GM, Töteberg-Harms M, Lewis R, Fea A, Marolo P, Ahmed IIK. Current review of excimer laser trabeculostomy. Eye Vis (Lond). 2020;7:24. 

  46. Krasnov MM. Laseropuncture of anterior chamber angle in glaucoma. Am J Ophthalmol. 1973;75(4):674–678. 

  47. Berlin MS, Shakibkhou J, Tilakaratna N, Giers U, Groth SL. Eight-year follow-up of excimer laser trabeculostomy alone and combined with phacoemulsification in patients with open-angle glaucoma. J Cataract Refract Surg. 2022;48(7):838–843. 

  48. Böke, H. History of cyclodialysis. In memory of Leopold Heine 1870–1940. Klin. Monatsblatter Augenheilkd. 1990;197:340–348.

  49. Gigon A, Shaarawy T. The suprachoroidal route in glaucoma surgery. J Curr Glaucoma Pract. 2016;10(1):13–20. 

  50. Johnson M. Unconventional aqueous humor outflow: a review. Exp Eye Res. 2017; 158: 94–111.

  51. Grierson I, Minckler D, Rippy MK, et al. A novel suprachoroidal microinvasive glaucoma implant: in vivo biocompatibility and biointegration. BMC Biomed Eng. 2020;2:10. 

  52. Dick HB, Mackert MJ, Ahmed IIK, et al. Two-year performance and safety results of the MINIject supraciliary implant in patients with primary open-angle glaucoma: meta-analysis of the STAR-I, II, III trials. Am J Ophthalmol. 2024;260:172–181. 

  53. Iantrek, Inc. Unlock natural outflow through the uveoscleral pathway: AlloFlo Uveo. Available from: https://iantrekmed.com/alloflo. Accessed on December 11, 2025. 

  54. Calvo E, De Francesco T, Vera L, Tyson F, Weinreb RN. Bio-interventional uveoscleral outflow enhancement surgery for primary open-angle glaucoma: 2-tyear results of cyclodialysis with scleral allograft reinforcement. Ophthalmol Sci. 2025; 5(4):100727.

  55. Ontario Health. Minimally invasive bleb surgery for glaucoma: a health technology assessment. Ont Health Technol Assess Ser. 2024;24(1):1–151. 

  56. Evers C, Böhringer D, Kallee S, et al. XEN®-63 compared to XEN®-45 gel stents to reduce intraocular pressure in glaucoma. J Clin Med. 2023;12(15):5043. 

  57. Hussein IM, De Francesco T, Ahmed IIK. Intermediate outcomes of the novel 63-μm gelatin microstent versus the conventional 45-μm gelatin microstent. Ophthalmol Glaucoma. 2023;6(6):580–591. 

  58. De Francesco T, Armstrong JJ, Hussein IM, Costa VP, Ahmed IIK. Mitomycin C 0.2 mg/ml versus Mitomycin C 0.4 mg/ml during the implantation of an ab externo polystyrene-isobutylene-styrene microshunt: a mega-analysis. Ophthalmol Glaucoma. 2024;7(5):454–465. 

  59. Governatori L, Oliverio L, Mermoud A, et al. PreserFlo MicroShunt versus trabeculectomy: an updated meta-analysis and systematic review. Graefes Arch Clin Exp Ophthalmol. 2025;263(4):885–899. 

  60. Verma-Fuehring R, Dakroub M, Bamousa A, Kann G, Hillenkamp J, Kampik D. The use of intraluminal PRESERFLO stenting in avoiding early postoperative hypotony. Graefes Arch Clin Exp Ophthalmol. 2024;262(12):3925–3932. 

  61. Arikan G, Gunenc U. Ahmed glaucoma valve implantation to reduce intraocular pressure: updated perspectives. Clin Ophthalmol. 2023;17:1833–1845. 

  62. New World Medical. New World Medical introduces the Ahmed ClearPath® ST Glaucoma drainage device. September 2, 2025. Available at: https://www.newworldmedical.com/new-world-medical-introduces-the-ahmed-clearpath-st-glaucoma-drainage-device. Accessed on December 1, 2025. 

  63. Shalaby WS, Reddy R, Wummer B, et al. Ahmed ClearPath vs. Baerveldt Glaucoma Implant: a retrospective noninferiority comparative study. Ophthalmol Glaucoma. 2024;7(3):251–259. 

  64. Grover DS, Kahook MY, Seibold LK, et al. Clinical outcomes of Ahmed ClearPath implantation in glaucomatous eyes: a novel valveless glaucoma drainage device. J Glaucoma. 2022;31(5):335–339. 

  65. Carlà MM, Gambini G, Boselli F, et al. The Paul Glaucoma Implant: a systematic review of safety, efficacy, and emerging applications. Graefes Arch Clin Exp Ophthalmol. 2025;263(9):2447–2459. 

  66. Bicket AK, Szeto J, Roeber P, et al. A novel bilayered expanded polytetrafluoroethylene glaucoma implant creates a permeable thin capsule independent of aqueous humor exposure. Bioeng Transl Med. 2021;6(1):e10179.

  67. Avisi Technologies presents positive six-month clinical data for VisiPlate Aqueous Shunt at the American Glaucoma Society. April 2, 2025. Available at: https://www.prnewswire.com/news-releases/avisi-technologies-presents-positive-six-month-clinical-data-for-visiplate-aqueous-shunt-at-the-american-glaucoma-society-302418787.html. Accessed on December 23, 2025.

  68. Glaucoma Today. The Calibreye System. June 2024. Available at: https://glaucomatoday.com/articles/2024-may-june/the-calibreye-system. Accessed on December 23, 2025.

  69. Nagy ZZ, Kranitz K, Ahmed IIK, De Francesco T, Mikula E, Juhasz T. First-in-human safety study of femtosecond laser image-guided trabeculotomy for glaucoma treatment: 24-month outcomes. Ophthalmol Sci. 2023;3(4):100313.

Ophthalmology Rounds is made possible through educational funding
from the following industry co-sponsors:

Supporters: Apotex, Astellas, Bayer

Friends: AbbVie, Alcon, Biocon, Celltrion, Roche

© 2026 Department of Ophthalmology and Vision Sciences, Faculty of Medicine, University of Toronto, which is solely responsible for the contents. Publisher: Snell Medical Communication Inc. in cooperation with the Department of Ophthalmology and Vision Sciences, Faculty of Medicine, University of Toronto. ®Ophthalmology Rounds is a registered trademark of Snell Medical Communication Inc. All rights reserved. The administration of any therapies discussed or referred to in Ophthalmology Rounds should always be consistent with the approved prescribing information in Canada. Snell Medical Communication Inc. is committed to the development of superior Continuing Medical Education.

bottom of page