Effectiveness and limitations of minimally invasive glaucoma surgery targeting Schlemm’s canal

Glaucoma surgery is performed to lower intraocular pressure (IOP); ideally, the IOP reduction is safely maintained for an extended period of time. Although trabeculectomy was considered the gold standard for glaucoma surgery for many years because of its effective IOP reduction, yet now it is considered unsafe because of serious complications. In recent years, minimally invasive glaucoma surgery (MIGS), which emphasizes safety and can be performed rapidly, has become widespread. Because MIGS does not involve conjunctival incisions, patients can undergo future trabeculectomy. If IOP reduction can be maintained safely, the number of anti-glaucoma drops can be reduced and visual function maintained, good outcomes for patients with glaucoma. Currently, many types of MIGS approved in Japan are reported to yield relatively good results, with targets of approximately 15–19 mmHg. However, the IOP-lowering effects of MIGS are limited. In procedures targeting Schlemm's canal, it is difficult to lower IOP beyond episcleral venous pressure. In some instances, a beneficial effect cannot be achieved if function is reduced beyond the collector channel. There are many unclear aspects regarding long-term outcomes following MIGS. Notably, investigation is ongoing to determine which patients are likely to benefit most from surgery. Based on previous reports, this review describes the characteristics and results of MIGS, approved in Japan, as well as underlying factors that affect the preoperative predictions and outcomes of the surgical procedure.