What are the recent advances in glaucoma surgeries that an ophthalmology resident should be familiar with?

Recent Advances in Glaucoma Surgeries

Minimally Invasive Glaucoma Surgery (MIGS)

MIGS represents the most significant paradigm shift in glaucoma surgery over the past decade, offering modest IOP reduction with superior safety profiles compared to traditional filtration surgery. 1, 2

Trabecular Micro-Bypass Stents

• iStent devices (first and second generation) have FDA approval specifically for implantation in combination with cataract extraction in patients with mild to moderate open-angle glaucoma, with pivotal trials showing significantly higher percentages of patients achieving unmedicated IOP ≤21 mmHg compared to phacoemulsification alone. 3, 4

• The second-generation iStent inject allows placement of multiple stents through a single corneal incision, with initial results demonstrating effective IOP reduction, though current coverage guidelines limit medically necessary implantation to a maximum of two stents per eye. 3, 4

• iStent Infinite represents the newest iteration, though systematic reviews indicate uncertainty regarding MIGS effectiveness compared to traditional surgeries, with the recency of approvals limiting conclusive long-term data. 1, 3

Canalicular Scaffold Devices

• The Hydrus microstent is a canalicular scaffold that spans approximately 90 degrees of Schlemm's canal, providing structural support to maintain patency of the conventional outflow pathway, with initial publications showing mean postoperative IOP reduction. 5, 4

Suprachoroidal Devices

• The CyPass microstent (now withdrawn from market) and iStent Supra target the suprachoroidal outflow pathway through ab interno approaches, representing attempts to enhance uveoscleral drainage. 5

Trabecular Ablation Procedures

• Trabectome (ab interno trabeculectomy) removes a strip of trabecular meshwork and inner wall of Schlemm's canal using electrocautery, with studies comparing phaco-Trabectome to phacotrabeculectomy showing less IOP reduction but fewer postoperative complications and similar success rates. 5, 4

• Kahook Dual Blade (KDB) and gonioscopy-assisted transluminal trabeculotomy (GATT) represent newer goniotomy techniques that excise or incise trabecular meshwork tissue to enhance conventional outflow. 5

• Excimer laser trabeculostomy (ELT) showed similar success rates to selective laser trabeculoplasty in comparative studies. 4

Bleb-Forming MIGS Procedures

Subconjunctival Drainage Devices

• The Xen gel stent is a soft collagen-derived gelatin tube (45 or 63 microns) implanted ab interno to create a subconjunctival filtration pathway, representing a minimally invasive alternative to traditional trabeculectomy. 5

• The InnFocus microshunt (PreserFlo MicroShunt) is an 8.5mm SIBS (poly[styrene-block-isobutylene-block-styrene]) tube with external fins to prevent migration, implanted through a conjunctival approach to create controlled subconjunctival filtration. 5

Advances in Traditional Glaucoma Surgery

Trabeculectomy Modifications

Recent trabeculectomy advancements focus on adjunctive incisions, Tenon's layer management, and novel suturing techniques to improve surgical outcomes and reduce complications. 2

• Releasable sutures allow postoperative titration of aqueous flow, though systematic reviews show uncertainty regarding their comparative effectiveness versus standard suturing. 1, 2

• Adjunctive use of antimetabolites (mitomycin C and 5-fluorouracil) improves IOP control after trabeculectomy with high-certainty evidence, representing one of the few areas with strong evidence in glaucoma surgery. 1

• Beta-irradiation as an alternative to antimetabolites shows improved IOP control after trabeculectomy in systematic reviews. 1

Glaucoma Drainage Devices (GDDs)

• Baerveldt shunts may lower IOP more than Ahmed shunts based on weak evidence, though overall uncertainty exists regarding comparative effectiveness of different aqueous shunts versus trabeculectomy. 1

• Recent modifications include novel surgical techniques to manage postoperative complications and surgical failure, with new GDD designs emerging to address traditional device limitations. 2

Nonpenetrating Glaucoma Surgery

Deep Sclerectomy

• Deep sclerectomy involves excision of sclerocorneal tissue under a partial-thickness scleral flap, leaving a thin trabecular meshwork window, with randomized trials showing either equal effectiveness or greater IOP reduction with trabeculectomy compared to deep sclerectomy. 1

Canaloplasty

• Canaloplasty combines circumferential viscodilation of Schlemm's canal using a flexible microcatheter with deep sclerectomy and placement of a 10-0 polypropylene suture within the canal to apply inward tension on trabecular meshwork, though retrospective series found lower postoperative IOP with trabeculectomy. 1

• No randomized clinical trials comparing trabeculectomy and canaloplasty exist, limiting evidence-based recommendations. 1

Laser Surgery Advances

Selective Laser Trabeculoplasty (SLT)

• SLT uses a 532 nm Q-switched frequency-doubled Nd:YAG laser that delivers less energy and is selectively absorbed by pigmented trabecular meshwork cells, producing less thermal damage than argon laser trabeculoplasty (ALT). 1

• High-certainty evidence demonstrates that laser trabeculoplasty is as effective as medical treatment as first-line therapy to control IOP, with the Glaucoma Laser Trial showing initial laser trabeculoplasty lowered IOP more (9 mmHg) than topical timolol (7 mmHg) over 2 years. 1

• SLT appears comparable to but not superior to ALT in lowering IOP, with similar IOP reduction and success rates observed with repeat SLT compared to initial SLT. 1

• 360-degree treatment with SLT is necessary to achieve comparable efficacy to prostaglandin analog therapy, with 90 and 180-degree treatments showing inferior IOP-lowering effects. 1

Cyclodestructive Procedures

• Transscleral cyclophotocoagulation has largely replaced cyclocryotherapy as the preferred cyclodestructive procedure due to less postoperative pain, reduced inflammation, and technical ease. 6

• Endoscopic cyclophotocoagulation (ECP) uses an 810-nm laser delivered through fiberoptic cable with direct visualization of ciliary processes, achieving IOP reduction of 34-57%, with increasing popularity for refractory glaucoma. 6

• Cyclocryotherapy is now considered only when laser equipment is unavailable or after failed laser cyclodestructive procedures, given higher risks of severe inflammation and pain. 6

Combined Cataract and Glaucoma Surgery

• Combined procedures result in modest IOP reduction of less than 2 mmHg on average, with the Ocular Hypertension Treatment Study showing 16.5% average IOP decrease after cataract extraction that persisted for 3 years postoperatively. 1

• Combined cataract and glaucoma surgery is generally not as effective as glaucoma surgery alone in lowering IOP, suggesting patients requiring filtration surgery with mild cataract may benefit from filtration surgery first and delayed cataract extraction. 1

• Use of mitomycin C (but not 5-fluorouracil) results in lower IOP in combined procedures, with moderate quality evidence suggesting separated incisions result in lower IOP than one-site procedures, though differences are small. 1

Critical Evidence Gaps and Clinical Implications

Systematic reviews reveal high uncertainty regarding MIGS effectiveness, with only 38% of glaucoma intervention reviews considered reliable, and most finding low-certainty evidence. 1

Areas with High-Certainty Evidence:

• Prostaglandin analogs are most effective medical treatment for lowering IOP 1
• Laser trabeculoplasty equals medical therapy as first-line treatment 1
• Trabeculectomy is more effective than medications for IOP reduction 1
• Antimetabolites improve trabeculectomy outcomes 1

Areas with Significant Uncertainty:

• Comparative effectiveness of different MIGS devices 1
• Long-term efficacy and safety of MIGS procedures 1, 5
• Optimal timing of surgical intervention 1
• Effectiveness of glaucoma drainage devices versus trabeculectomy 1

Common Pitfalls and Caveats

• MIGS devices provide modest IOP reduction (typically 15-25% reduction) compared to trabeculectomy (40-60% reduction), making them inappropriate for patients requiring aggressive IOP lowering. 1, 2

• Coverage limitations restrict iStent implantation to a maximum of two devices per eye and require concurrent cataract surgery, with three-stent procedures considered investigational. 3

• IOP spikes occur in 4.5-27% of eyes after selective laser trabeculoplasty, with heavily pigmented trabecular meshwork increasing risk, necessitating IOP checks within 30 minutes to 2 hours post-procedure. 1

• All cyclodestructive procedures carry risks of vision loss, hypotony, and phthisis bulbi, requiring careful patient selection and informed consent. 6

• Publication bias and lack of long-term randomized trials limit conclusive recommendations for many newer procedures, with most MIGS evidence derived from industry-sponsored studies with short follow-up. 1, 5