Primary angle-closure glaucoma is a type of glaucoma caused by the peripheral iris blocking the trabecular meshwork, or permanently adhering to the trabecular meshwork, obstructing the outflow of aqueous humor, leading to increased intraocular pressure. It is characterized by a narrow angle and the anatomical feature of the peripheral iris being prone to contact with the trabecular meshwork. Gonioscopy confirming angle closure is an important diagnostic criterion. The characteristic of open-angle glaucoma, however, is that even though intraocular pressure is elevated, the angle remains open, with the obstruction of aqueous outflow occurring at the trabecular meshwork system.