MIGS procedures constitute a group of surgical interventions which share five characteristics5:
1. High safety profile: MIGS carry a much lower risk of serious complications such as hypotony, choroidal effusions, or choroidal hemorrhages.
2. Minimal disruption of normal anatomy: MIGS allow for enhancement of physiological outflow mechanisms avoiding significant alterations in normal ocular anatomy.
3. Ab interno approach: MIGS are typically performed ab interno through a traditional clear corneal wound with direct visualization of the anatomical target.
4. Efficacy: MIGS should offer a meaningful IOP lowering effect. The IOP reduction level is often inferior to traditional filtering surgery but should be at least 20%. Alternatively, patients who do not experience an IOP decrease should attain the reduction of at least one medication.
5. Ease of use for patients and physicians: MIGS should allow for rapid recovery with minimal additional downtime for patients. They should also be easily incorporated into traditional phacoemulsification surgery.
MIGS offer IOP lowering by targeting various aspects of normal aqueous dynamics. The first approaches involve enhancing outflow across the trabecular meshwork and through Schlemm’s canal. The juxtacanalicular trabecular meshwork has traditionally been identified as the site of greatest resistance to aqueous outflow. This resistance can be overcome through bypassing or removing this tissue to lower IOP through increased outflow. The bypass can be achieved by placing a trabecular meshwork bypass stent, allowing aqueous to flow directly through the stent from the anterior chamber into Schlemm’s canal. Another approach to bypass the trabecular meshwork resistance is goniotomy or trabeculectomy, which involves a surgical incision and or excision of this tissue and allows for improved aqueous outflow into Schlemm’s canal. Dilation of Schlemm’s canal through cannulation and expansion with viscoelastic is yet another approach to enhance outflow through the normal physiologic aqueous outflow system.
The second group of MIGS approaches seeks to increase outflow via alternate pathways. The uveoscleral outflow pathway can be augmented by accessing the suprachoroidal space with microstent placement. Alternatively, suppose traditional outflow pathways are unlikely to be improved. In that case, aqueous can be shunted into the subconjunctival space through an ab interno, small incision approach.
A third MIGS approach involves decreasing aqueous production by ablation of the ciliary body. This approach is employed during endocyclophotocoagulation. An endoscopic laser probe is inserted through a clear corneal incision. It is directly used to visualize and ablate the ciliary body.
Information on this treatment was written by Babak Eliassi-Rad, MD, Vikas Singh, MD