What are the differences between iStent (Micro-Invasive Glaucoma Surgical device) G2 and Infinite for a patient with glaucoma requiring surgical intervention?

iStent Infinite vs iStent G2 for Glaucoma Surgery

The iStent Infinite (3 iStent inject W stents) is the superior choice for patients with refractory glaucoma uncontrolled by prior surgery or maximum medical therapy, while iStent G2 (2 first-generation stents) is appropriate for mild-to-moderate open-angle glaucoma combined with cataract surgery. 1, 2, 3

Key Device Differences

iStent Infinite

• Configuration: Three second-generation iStent inject W stents preloaded in a single injector 1
• FDA indication: Stand-alone procedure for open-angle glaucoma uncontrolled by prior incisional/cilioablative surgery or maximum tolerated medical therapy 1
• IOP reduction: Achieves mean 5.9 mmHg reduction in MDIOP (25% reduction from baseline of 23.4 mmHg) 1
• Medication reduction: 76.1% of patients achieve ≥20% IOP reduction on same or fewer medications at 12 months 1
• Patient population: Designed for refractory cases with failed prior surgeries (mean 3.1 medications at baseline) 1

iStent G2 (Original iStent)

• Configuration: Two first-generation trabecular bypass stents implanted sequentially 2, 4
• FDA indication: Combined with cataract extraction in mild-to-moderate open-angle glaucoma on topical medications 2, 3
• IOP reduction: Achieves postoperative pressures typically in mid-to-upper teens (modest reduction) 2, 3
• Medication reduction: 1.38 times more likely to be drop-free at 6-18 months when combined with phacoemulsification versus phacoemulsification alone 4
• Patient population: Primarily for earlier-stage disease with concurrent cataract 2, 4

Clinical Decision Algorithm

Choose iStent Infinite when:

• Prior failed glaucoma surgery (trabeculectomy, tube shunt, or other MIGS) with persistent IOP elevation 1
• Maximum tolerated medical therapy (typically ≥3 medications) with inadequate IOP control 1
• Stand-alone glaucoma procedure needed without concurrent cataract surgery 1
• Baseline IOP >20 mmHg on medications, requiring more aggressive IOP reduction 1
• Refractory disease where traditional MIGS has insufficient efficacy 1

Choose iStent G2 when:

• Mild-to-moderate open-angle glaucoma with concurrent visually significant cataract 2, 3
• Baseline IOP <18 mmHg on 1-2 medications, where modest reduction is acceptable 5
• First-line surgical intervention in medication-responsive disease 2, 4
• Patient age >70 years (some evidence suggests better outcomes with iStent in this demographic) 5
• Combined procedure with phacoemulsification is planned 2, 3, 4

Comparative Efficacy Data

IOP Reduction Magnitude

• iStent Infinite: Mean 5.9 mmHg reduction from medicated baseline of 23.4 mmHg (25% reduction) in refractory cases 1
• iStent G2: Mean 0.42 fewer drops required, with very low-quality evidence for IOP reduction magnitude 4
• Critical distinction: iStent Infinite tested in more severe disease (failed prior surgery), while G2 primarily studied with concurrent cataract surgery 1, 4

Medication Burden Reduction

• iStent Infinite: 53% achieve ≥30% MDIOP reduction without additional interventions; mean reduction from 3.1 to fewer medications 1
• iStent G2: Mean reduction of 0.42 drops when combined with phacoemulsification versus phacoemulsification alone 4

Success Rates

• iStent Infinite: 76.1% responder rate (≥20% IOP reduction on same/fewer medications) at 12 months 1
• iStent G2: >90% drop-free versus medical therapy alone, but with very low-quality evidence 4

Safety Profile Comparison

iStent Infinite Safety

• No explants, infections, or device-related interventions reported in pivotal trial 1
• No hypotony observed 1
• Favorable safety despite use in refractory post-surgical eyes 1

iStent G2 Safety

• Low complication rates, most commonly stent malposition or obstruction 2, 3
• More favorable safety profile than trabeculectomy or tube shunts in short-term 2, 3
• Similar secondary surgery rates when combined with phacoemulsification versus phacoemulsification alone 4

Critical Evidence Quality Considerations

The evidence base for both devices has significant limitations 2:

• Very low-quality evidence overall for iStent effectiveness according to 2021 Cochrane systematic review 2, 4
• Uncertainty regarding MIGS effectiveness compared to traditional surgery persists 2, 3
• No head-to-head randomized trials comparing iStent Infinite versus iStent G2 exist
• Industry funding (Glaukos Corporation) for all major trials raises potential bias concerns 4
• Limited long-term data beyond 24-47 months for both devices 2, 3, 6

Common Pitfalls to Avoid

Device Selection Errors

• Do not use iStent G2 as stand-alone procedure - it is FDA-approved only with concurrent cataract surgery 2, 3
• Do not expect trabeculectomy-level IOP reduction - both devices achieve modest reductions (mid-to-upper teens) 2, 3
• Do not use in angle-closure glaucoma - both devices require open-angle anatomy 2, 4, 1

Preoperative Requirements

• Perform gonioscopy preoperatively to confirm adequate trabecular meshwork visualization and open-angle anatomy 3
• Document baseline IOP on and off medications to establish realistic postoperative targets 1
• Assess prior surgical history - iStent Infinite specifically designed for failed prior surgery cases 1

Postoperative Expectations

• Multiple stents provide better IOP lowering - studies show 2-3 stents superior to single stent 2, 4
• Postoperative pressures typically mid-to-upper teens - counsel patients this is less reduction than trabeculectomy 2, 3
• Medication reduction is common but not universal - 45-53% medication-free rates reported 6, 1

Surgical Technique Considerations

iStent Infinite Implantation

• Stand-alone ab interno approach through clear corneal incision 1
• Three stents placed in single procedure using preloaded injector 1
• Gonioscopic guidance required for proper Schlemm's canal placement 1

iStent G2 Implantation

• Combined with phacoemulsification in same surgical session 2, 3, 4
• Two stents placed sequentially into Schlemm's canal 2
• Heparin-coated titanium snorkel-shaped devices 2

When Neither Device is Appropriate

Consider trabeculectomy or tube shunt instead when 2:

• Target IOP <12-14 mmHg required (MIGS insufficient for low targets) 2, 3
• Advanced glaucoma with severe visual field loss requiring maximal IOP reduction 2
• Closed-angle anatomy or extensive peripheral anterior synechiae 2
• Prior MIGS failure requiring more definitive filtration surgery 2