outflow. current definition of MIGS, but have
outflow. The procedure is performed with an illuminated microcatheter (iTrack 250A; Ellex) that is inserted via a corneal microincision. It restores the natural outflow pathway with minimal tissue trauma by viscodilation and leaves no foreign body (tensioning suture or stent) in the eye. ABiC is also the only MIGS procedure that addresses collector channel blockages as well.Excimer laser trabeculostomy: Excimer laser trabeculostomy (ELT) is a form of ab interno trabeculotomy, that precisely ablates the trabecular meshwork without causing thermal injury to or scarring of the surrounding tissue.1-3 This procedure uses a XeCl (308-nm) excimer laser coupled to an intraocular fiber optic delivery system to create long-term anatomic openings that connect the anterior chamber directly to Schlemm canal.
The photoablative conversion of trabecular meshwork tissue into gas enables pneumatic canaloplasty. NB: The following surgeries do not fit in into the current definition of MIGS, but have been traditionally classified in this group, since they are relatively newer surgeries. They are being mentioned in this review for the sake of completion.Non-Penetrating Glaucoma Surgeries: Aqueous egress is known to occur at the level of Schlemms Canal (SC) and its efferents and the selective removal of the inner wall of SC and the adjacent trabecular meshwork, leaving intact the innermost trabecular meshwork layers decreases the resistance to aqueuos outflow. The residual membrane, formed by the anterior and posterior trabecular meshwork, the internal endothelium of Schlemm’s canal and Descemet’s membrane in deep sclerectomy or viscocanalostomy, retains a degree of residual outflow resistance, making this surgery safer. Since the anterior chamber (AC) is not entered, these group of surgeries are called non-penetrating glaucoma surgeries CO2 laser assisted DS: CO2 laser energy ablates the underlying sclera layer by layer until the roof of SC is exposed. At that point fluid percolates in the thinned tissue and prevents further ablation, thus preventing a full thickness perforation.
The laser thus is the fancy knife that makes the surgery safer, easier to perform, with decreased rates of perforations into the AC. Canaloplasty: Canaloplasty and viscocanalostomy are procedures that rely on dilation of the SC to decrease outflow resistance. The tensioning suture within the SC, similar to the action of pilocarpine, as well as helps in maintaining a patent canal lumen.