Trabeculectomy is a 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. Rarely general anaesthesia will be used, in patients with an inability to cooperate during surgery.
An initial pocket is created under the conjunctiva and Tenon’s capsule and the wound bed is treated for several seconds to minutes with mitomycin C soaked sponges. These chemotherapeutics help to prevent failure of the filter bleb from scarring by inhibiting fibroblast growth. Some surgeons prefer “fornix-based” conjunctival incisions while others use “limbus-based” construction at the corneoscleral junction which may allow easier access in eyes with deep sulci. A partial thickness flap with its base at the corneoscleral junction is then made in the sclera after careful cauterization of the flap area, and a window opening is created under the flap to remove a portion of the sclera, Schlemm’s canal and the trabecular meshwork to enter the anterior chamber. Because of the fluid egress the iris will partially prolapse through the sclerostomy, an iridectomy will prevent future blockage of the sclerostomy. The scleral flap is then sutured loosely back in place with several sutures. The conjunctiva is closed in a watertight fashion at the end of the procedure.
Procedure
Intraocular pressure may be lowered by allowing drainage of aqueous humor from within the eye to the following routes: (1) filtration through the sclerostomy around the margins of the scleral flap into the filtering bleb that forms underneath the conjunctiva, (2) filtration through outlet channels in the scleral flap to underneath the conjunctiva, (3) filtration through connective tissue of the scleral flap to underneath the conjunctiva. into cut ends of Schlemm’s canal, (4) aqueous flow into cut ends of Schlemm’s canal into collector channels and episcleral veins and (5) into a cyclodialysis cleft between the ciliary body and the sclera if tissue is dissected posterior to the scleral spur.
Postoperative Care
Glaucoma medications are usually discontinued to improve aqueous humor flow to the bleb. Topical medications consist typically of antibiotic drops four times per day and anti-inflammatory therapy e.g. with prednisolone drops every two hours. A shield is applied to cover the eye until anesthesia has worn off (that also anesthetizes the optic nerve) and vision resumes.
Patients are instructed to call immediately for pain that cannot be controlled with over the counter pain medication or if vision decreases, to not rub the eye and to wear the shield at night for several days after surgery.
In the following days to weeks sutures that hold the scleral flap down can be cut by laser suture lysis to titrate the intraocular pressure down by improving outflow. In laser suture lysis a red light laser and a contact lens are used to penetrate noninvasively the overlying conjunctiva and cut the black nylon suture. Some surgeons prefer adjustable flap sutures during the trabeculectomy that can be loosened later on with forceps in a slit lamp office procedure.