Trabeculectomy & Filtration Surgery

Surgical Technique

Trabeculectomy creates an alternate drainage route for aqueous under the conjunctiva. A partial-thickness scleral flap acts as a variable-resistance valve over a full-thickness sclerostomy opening into the anterior chamber, and together the two let aqueous percolate into the subconjunctival space and form a filtering bleb without draining so freely that the eye overfilters. A peripheral iridectomy is added at the same time so the iris cannot prolapse into the sclerostomy and occlude it, a complication that can cause bleb failure or acute angle closure.

Mitomycin C (MMC) is the primary antifibrotic used intraoperatively. It alkylates DNA and inhibits fibroblast proliferation at the scleral flap and conjunctival wound, limiting the scarring that would otherwise doom the bleb to failure. Scleral flap sutures tied tightly at the time of surgery can later be cut selectively in clinic with laser suture lysis. This titrates aqueous outflow and adjusts IOP after the fact, with no second trip to the operating room.

Postoperative Assessment & Complications

The Seidel test detects aqueous leakage with fluorescein dye. A dilute, streaming pattern in the dye marks an active wound leak that needs management, whether the leak is coming from the bleb itself or from the surgical wound.

Bleb overfiltration shows up weeks after surgery as a shallow anterior chamber, low IOP, and choroidal effusions: too much aqueous escapes, hypotony sets in, and the shallow chamber and serous effusions follow directly from that. If the hypotony persists, scleral and choroidal collapse can progress to hypotony maculopathy, chorioretinal folds and disc swelling that can be mistaken for papilledema on exam. An encapsulated bleb (Tenon's cyst) sits at the other end of the spectrum, with fibrous walling-off of the drainage pathway driving IOP back up instead. First-line management there is bleb needling with adjunctive antimetabolite injection, reserving revision surgery for cases that don't respond.

Malignant glaucoma (aqueous misdirection) causes the opposite picture: a shallow chamber with IOP climbing rather than falling, because aqueous is pushed posteriorly behind the vitreous instead of draining forward through the bleb. A patent peripheral iridectomy rules out pupillary block as the cause. First-line treatment is cycloplegics such as atropine, which tighten the zonules and pull the lens-iris diaphragm backward; miotics make the misdirection worse and are contraindicated. Medical therapy resolves roughly half of cases within days, and eyes that don't respond go on to laser hyaloidotomy or, if that fails, pars plana vitrectomy to remove the vitreous driving the cycle.

Bleb morphology also predicts long-term infection risk. A thin-walled, avascular, cystic bleb, often seen after antimetabolite use, has a compromised epithelial barrier and predisposes to late bleb-related endophthalmitis. A thick-walled, vascularized, diffuse bleb carries far less of that risk.