sentences:  Filtering procedures are typically divided into either penetrating or non-penetrating types depending upon whether an intraoperative entry into the anterior chamber occurs.Penetrating filtering surgeries are further subdivided into guarded filtering procedures, also known as protected, subscleral, or partial thickness filtering procedures (in which the surgeon sutures a scleral flap over the sclerostomy site), and full thickness procedures.Trabeculectomy is a guarded filtering procedure that removes of part of the trabecular meshwork.