Lecture done by Dr. Deya al btoush, commentary Prof. Khalil Alsalem
Microinvasive (or minimally invasive) glaucoma surgery (MIGS) has emerged over the last 15–20 years as a response to the limitations of traditional filtering surgery. For decades, trabeculectomy was the gold standard for surgical IOP lowering, capable of achieving very low target pressures. However, this comes at the cost of substantial morbidity: hypotony, bleb leaks, infection, accelerated cataract, and intensive postoperative care. As patients live longer and visual expectations rise; the need for procedures that balance efficacy with safety and faster recovery has pushed surgeons toward Microinvasive glaucoma surgery.
MIGS was conceived to “fill the gap” between medications/laser and trabeculectomy or tube shunts. These procedures, are usually ab interno. the operation spares the conjunctiva, use micro-incisional techniques, and aim for a favorable safety profile and rapid rehabilitation. The trade-off is that MIGS generally delivers modest IOP lowering compared with trabeculectomy. Making it particularly attractive for mild to moderate open-angle glaucoma, often combined with phacoemulsification.
Classification of MIGS
Most contemporary reviews classify MIGS according to the aqueous humor pathway. Microinvasive glaucoma surgery targets trabecular/Schlemm’s canal, suprachoroidal (uveoscleral), subconjunctival, or ciliary body–targeted (aqueous suppression). This framework helps position the expanding list of devices and procedures.
Trabecular and Schlemm’s canal–based MIGS
This is the largest and most established group. Designed to bypass or remove trabecular resistance while keeping episcleral venous pressure as the floor.
Trabecular micro-bypass stents
iStent family (Glaukos) – The original iStent was the first FDA-approved MIGS device. A tiny heparin-coated titanium snorkel inserted into Schlemm’s canal. Subsequent generations include iStent inject, iStent inject W (two stents preloaded in one injector) and iStent infinite for standalone use. These are typically combined with cataract surgery in mild–moderate POAG. Producing modest IOP and medication reductions with an excellent safety profile.
Hydrus Microstent (Alcon) – A nitinol crescent stent that dilates ~90° of Schlemm’s canal and bypasses the trabecular meshwork. Randomized data show greater IOP and medication reduction versus phaco alone, with durable outcomes to at least 5 years.
Excisional and transluminal trabecular procedures
These are “device-assisted” more than “device-implanting,” but are widely grouped within MIGS:
Kahook Dual Blade (KDB) – A single-use blade that performs excisional goniotomy. Removing a strip of trabecular meshwork and inner Schlemm’s wall via an ab interno approach.
Trabectome – Uses electrocautery to ablate a segment of trabecular meshwork and inner Schlemm’s wall, also ab interno.
GATT (gonioscopy-assisted transluminal trabeculotomy) – A 360° trabeculotomy created with a microcatheter or suture passed through Schlemm’s canal.
OMNI Surgical System / ABiC (iTrack) – Canaloplasty-style viscodilation combined with trabeculotomy (OMNI) or standalone ab interno canaloplasty (ABiC/iTrack Advance). Targeting collector channels as well as Schlemm’s canal.
These techniques offer greater IOP reduction than single trabecular stents in some series, but with more hyphema and a slightly more “surgical” feel, while still preserving the conjunctiva.
Suprachoroidal / supraciliary MIGS
The suprachoroidal space exploits the uveoscleral pathway and a favorable hydrostatic gradient. Interest in this route has resurged with modern materials.
CyPass Micro-Stent (Alcon) – historical, now withdrawn
CyPass was a polyimide microstent implanted ab interno into the supraciliary space, commonly combined with phaco. Early results showed good IOP reduction, but the 5-year COMPASS XT extension trial revealed significantly greater corneal endothelial cell loss (ECL) in the CyPass + phaco group compared with phaco alone. This led to a voluntary global market withdrawal in 2018, and unused devices were recalled. CyPass has thus become an important cautionary example in the MIGS story, underlining the need for long-term safety data and careful implant positioning.
iStent Supra
The iStent Supra is a heparin-coated polyethersulfone/titanium supraciliary stent implanted via a clear corneal, ab interno approach. Often in conjunction with phacoemulsification. It has CE approval in Europe and has been under clinical investigation in the US, with studies demonstrating promising IOP and medication reductions.
MINIject (Suprachoroidal gelatin implant)
MINIject is a porous, soft, supraciliary implant designed to maintain a controlled connection between the anterior chamber and the supraciliary space without a bleb. Recent prospective and real-world data show substantial and sustained IOP lowering (often into the low-teens) and medication reduction with acceptable ECL and a good safety profile, and it is currently the only commercially available device specifically targeting the supraciliary space.
Subconjunctival / bleb-forming MIGS-like devices
These procedures blur the boundary between classic filtering surgery and MIGS because they create a subconjunctival bleb, but they are minimally invasive and often included in extended MIGS classifications.
XEN Gel Stent (Allergan/AbbVie) – A 6-mm cross-linked gelatin tube (commonly XEN45) implanted ab interno (or ab externo) from the anterior chamber to the subconjunctival space. It provides controlled resistance and forms a low, diffuse bleb. XEN can achieve lower IOP than many trabecular MIGS options but shares bleb-related complications such as needling, leaks, or fibrosis.
PreserFlo MicroShunt (Santen) – An 8.5-mm SIBS (poly(styrene-block-isobutylene-block-styrene)) tube implanted ab externo into the subconjunctival space. It is more similar to a modern mini-trabeculectomy than classic Microinvasive glaucoma surgery but often discussed in the same spectrum of “minimally invasive” filtering procedures, achieving low teens IOP with a bleb-dependent mechanism.
Ciliary body–targeted MIGS
A third, smaller group of MIGS procedures reduces aqueous production rather than enhancing outflow.
Endocyclophotocoagulation (ECP) uses an endoscopic diode laser introduced through a clear corneal incision to directly visualize and ablate the ciliary processes. It is frequently combined with phacoemulsification in moderate glaucoma.
Other technologies such as micropulse transscleral cyclophotocoagulation are often considered “minimally invasive” but are external and usually categorized separately.
Where MIGS fits today
Taken together, Microinvasive glaucoma surgery has not replaced trabeculectomy and tube shunts for advanced, low-target IOP cases, but it has significantly changed the surgical algorithm. For patients with mild to moderate POAG, particularly those undergoing cataract surgery, trabecular or suprachoroidal MIGS offers additive IOP and medication reduction with a far lower risk profile than traditional filtering surgery. Subconjunctival microshunts bridge toward more aggressive surgery when lower pressures are required but still aim to simplify the postoperative course.
The story of CyPass underscores that “ minimally invasive glaucoma surgery ” does not automatically mean “benign,” and long-term data—especially on the corneal endothelium—are essential as new devices like MINIject, newer iStent generations, and combined canal-based systems evolve. Going forward, careful patient selection, mastery of gonioscopy, and a clear understanding of each device’s mechanism and risk profile will be critical as surgeons continue their shift from a trabeculectomy-centric era to a more nuanced, MIGS-based surgical strategy.