Ab interno Schlemm's Canal Surgery

Abstract

In primary open-angle glaucoma, the site of greatest resistance to aqueous outflow is thought to be the trabecular meshwork (TM) and inner wall of Schlemm's canal. Augmentation of the conventional (trabecular) outflow pathway can facilitate physiologic outflow and subsequently lower intraocular pressure. The most recent approach to enhancing the conventional outflow pathway is via an internal approach to the TM and Schlemm's canal. Ab interno Schlemm's canal surgery includes 4 novel surgical approaches: (1) removal of the TM and inner wall of Schlemm's canal by an internal approach (ab interno trabeculectomy), (2) implantation of a microstent to bypass the TM, (3) disruption of the TM and inner wall of Schlemm's canal via an internal approach (ab interno trabeculotomy), and (4) dilation of Schlemm's canal via an internal approach (ab interno canaloplasty). The first category includes the Trabectome (Neomedix, Tustin, CA, USA), and Kahook Dual Blade (New World Medical, Rancho Cucamonga, CA, USA). The second category includes the iStent (Glaukos, Laguna Hills, CA, USA), as well as the investigational Hydrus Microstent implant (Ivantis, Irvine, CA, USA). The third category includes gonioscopic-assisted transluminal trabeculotomy (iSciences catheter; Ellex, Adelaide, Australia), and 360° suture trabeculotomy (TRAB360, Sight Sciences, Menlo Park, CA, USA). The fourth category includes ab interno canaloplasty or AbiC (Ellex), and Visco360 (Sight Sciences). In contrast to external filtration surgeries, such as trabeculectomy and aqueous tube shunt, these procedures are categorized as internal filtration surgeries and are performed from an internal approach via gonioscopic guidance. Published results suggest that these surgical procedures are both safe and efficacious for the treatment of open-angle glaucoma.

12-Month Outcomes of Goniotomy Performed Using the Kahook Dual Blade Combined with Cataract Surgery in Eyes with Medically Treated Glaucoma

“…The traditional goniotomy knife, usually a microvitreoretinal blade, is used to incise the trabecular meshwork behind Schwalbe’s line and produces a single incision in the TM. Unfortunately, this technique does not remove TM tissue and may result in injuries to the adjacent sclera [ 10 ]. Potential reasons for short- and long-term failure of incisional goniotomy include fusion of residual TM leaflets as well as scleral damage with resulting inflammation and localized scarring response [ 11 , 12 ].…”

“…Potential reasons for short- and long-term failure of incisional goniotomy include fusion of residual TM leaflets as well as scleral damage with resulting inflammation and localized scarring response [ 11 , 12 ]. The KDB is a new ophthalmic blade, designed to remove the TM in a more complete fashion with minimal residual TM leaflets and less collateral damage [ 10 ].…”

Canaloplasty versus Nonpenetrating Deep Sclerectomy: 2-Year Results and Quality of Life Assessment

“…Although it requires surgical skills at a certain high level and is technically challenging, it has aroused growing interest among glaucoma surgeons, which has resulted in numerous papers published on the subject. Also, various modifications of the classic procedures were proposed, yet not all published but presented at congresses such as canaloplasty ab interno [ 3 , 4 ], canaloplasty with suprachoroidal drainage [ 5 ], or with an alternative system for intubation without viscodilation [ 6 ]. This procedure is very appealing to glaucoma surgeons, especially because it boosts the anatomy and physiology of the eye and restores natural outflow pathways of aqueous humor [ 2 ].…”

Evolution of canaloplasty and its direction

“…As no suture is placed into the SC, the SC is only enlarged by viscoelastic agents. Data from non-peer-reviewed articles showed that ABiC alone or combined with phacoemulsification achieved significant IOP lowing effect in open angle glaucoma patients [10]. However, we still do not know whether the expanding suture which is placed in the SC during standard canaloplasty plays a role in reducing the IOP of glaucoma patients, for there is no clinical study that compares the efficacy between standard canaloplasty and ABiC.…”

“…Ab interno canaloplasty (ABiC) is a minimally invasive glaucoma surgery [9,10]. ABiC is less invasive and safer than standard canaloplasty.…”