Glaucoma is a progressive eye condition characterized by damage to the optic nerve, which transmits visual information from the eye to the brain. A primary risk factor is chronically high intraocular pressure (IOP), caused by an imbalance in the eye’s fluid drainage system. The goal of all glaucoma treatment is to lower this internal eye pressure to prevent further optic nerve deterioration and vision loss. When eye drops and laser procedures are not effective, surgical intervention becomes necessary to regulate the fluid. Surgical management has advanced significantly with the introduction of newer, less invasive options.
Defining Minimally Invasive Glaucoma Surgery
Minimally Invasive Glaucoma Surgery (MIGS) represents a collection of procedures designed to reduce intraocular pressure with less tissue disruption than traditional methods. The core philosophy involves using microscopic instruments and very small incisions, often through the clear cornea, to access the eye’s internal drainage system. This approach is referred to as ab interno, meaning the procedure is performed from inside the eye.
MIGS procedures focus on enhancing the eye’s existing natural pathways for fluid drainage, rather than creating a new external channel. By minimizing trauma to surrounding tissues, these surgeries aim for a high safety profile and rapid recovery. The common goal is improving the outflow of aqueous humor, the fluid responsible for maintaining eye pressure.
How MIGS Procedures Lower Eye Pressure
MIGS procedures lower eye pressure by targeting the various points of resistance in the eye’s fluid dynamics. Most techniques focus on the conventional outflow pathway, which is the primary route for aqueous humor drainage. This pathway involves the fluid passing through the trabecular meshwork and into Schlemm’s canal.
Trabecular Outflow Enhancement
The trabecular meshwork is often the site of greatest resistance in eyes with open-angle glaucoma. Procedures in this category work by either bypassing or removing a portion of this meshwork to increase fluid flow. For example, micro-stents are implanted directly into the meshwork to create a permanent bypass from the anterior chamber into Schlemm’s canal. Other methods involve ablating or excising the trabecular meshwork tissue to clear the blockage and restore the natural drainage route.
Suprachoroidal and Subconjunctival Outflow
Some MIGS procedures enhance alternative drainage routes, such as the uveoscleral or subconjunctival pathways. The uveoscleral pathway, sometimes called the suprachoroidal space, is a secondary drainage system augmented by shunts. These devices redirect the aqueous humor into the space between the choroid and the sclera, utilizing the eye’s natural absorption capabilities. Shunting fluid to the subconjunctival space is typically reserved for patients needing a greater degree of pressure reduction.
Ideal Candidates and Procedure Context
MIGS is typically intended for patients with mild to moderate open-angle glaucoma whose intraocular pressure is not adequately managed by eye drops or laser treatment. These individuals require a moderate reduction in eye pressure but do not yet need the maximum effect provided by more invasive traditional surgeries. Patient selection focuses on those whose disease is not yet severe but who need better control to prevent further progression.
The procedure is frequently performed concurrently with cataract surgery, a combination known as phaco-MIGS. This approach is efficient because the surgeon uses the same small corneal incision for both procedures, adding only a few minutes to the total operating time. Combining the surgeries reduces the patient’s overall recovery period. Removing the cataractous lens can sometimes slightly improve the eye’s drainage angle, and the MIGS device offers a further, sustained reduction in pressure and decreased reliance on daily medication.
Comparing MIGS to Traditional Glaucoma Surgery
Minimally Invasive Glaucoma Surgery differs significantly from traditional filtration surgeries, such as trabeculectomy or tube shunt implantation. Traditional surgeries are reserved for more advanced cases because they create a new, controlled external drainage pathway involving more tissue manipulation. This approach achieves a dramatically lower intraocular pressure, often necessary for patients with severe optic nerve damage.
Traditional surgeries involve longer surgical time, greater alteration of eye anatomy, and a more intensive post-operative recovery. They carry a higher risk of complications, including infection, excessive scarring, and hypotony (pressure that is too low). In contrast, MIGS procedures are characterized by rapid recovery and a favorable safety profile, avoiding many complications associated with conventional filtering procedures.