Trabeculectomy is the most common invasive surgical procedure used in the treatment of glaucoma to relieve intraocular pressure by removing part of the eye's trabecular meshwork and adjacent structures. It is the most common glaucoma surgery performed and allows drainage of aqueous humor from within the eye to underneath the conjunctiva where it is absorbed. This outpatient procedure was most commonly performed under monitored anesthesia care using a retrobulbar block or peribulbar block or a combination of topical and subtenon (Tenon's capsule) anesthesia. Due to the higher risks associated with bulbar blocks, topical analgesia with mild sedation is becoming more common. Rarely general anesthesia will be used, in patients with an inability to cooperate during surgery. Trabeculectomy is highly effective in the treatment of advanced glaucoma as demonstrated in major glaucoma studies. Even if a prior trabeculectomy has failed a second trabeculectomy can be performed at a different site. If scarring is the main reason, anti-fibrotic and anti-inflammatory therapy has to be intensified in the second procedure. Alternatively, insertion of a glaucoma valve device can be used.