Trabeculectomy(also called glaucoma filtration surgery or fistulization of the sclera) is the gold-standard incisional surgery for glaucoma when medications and laser therapy have failed to adequately control IOP. The procedure creates a guarded fistula — a small, controlled opening through the sclera and trabecular meshwork — covered by a partial-thickness scleral flap that acts as a trapdoor, allowing aqueous humor to escape the anterior chamber and collect beneath the conjunctiva in a blister-like reservoir called a filtering bleb, where it is gradually reabsorbed. The scleral flap is sutured to regulate outflow and prevent hypotony. Antifibrotic agents — most commonly Mitomycin-C (MMC) or 5-fluorouracil (5-FU) — are applied intraoperatively (or injected postoperatively) to inhibit scarring and prolong bleb patency. A peripheral iridectomy is typically included to prevent iris from obstructing the fistula. The procedure is performed ab externo (from outside the eye). Key complications include hypotony, choroidal detachment, bleb failure/scarring, endophthalmitis (bleb-related), and cataract formation (in approximately one-third of patients).
latin + greek The word is a compound of three elements:
Trabecula: Diminutive of Latin trabs (“beam, timber, bar”) — referring to the lattice-like, beam-structured meshwork of tissue through which aqueous humor drains; in anatomy, a trabecula is any small, bar-like structural element.
-ec-: From Greek ek- (“out, away”) — the preposition of removal in surgical terminology.
-tomy: From Greek tomē (“a cutting”) — but here paired with the full suffix -ectomy (ektomē = “act of cutting out”), denoting surgical excision.
The combining form trabecul- appears in related terms: trabeculoplasty, trabeculotomy, trabeculodialysis. The first trabeculectomy was described by Koryllos (Greece) and Cairns (UK) nearly simultaneously in 1968, though the technique traces conceptual roots to earlier scleral fistulization procedures.
Fistulization of sclera for glaucoma; trabeculectomy ab externo — with scarring from previous ocular surgery or trauma (includes injection of antifibrotic agents)
Other Scleral Fistulization Procedures (Older / Less Common)
Revision or repair of operative wound of anterior segment, any type, early or late
Combined Phacotrabeculectomy
When cataract surgery (66984 or 66982) is performed in the same session as trabeculectomy (66170 or 66172), both codes may be reported with modifier 51 (multiple procedure). Confirm payer-specific bundling rules and CCI edits before reporting together.
Key Coding Tips
66170 vs. 66172: The critical distinction is prior surgery/scarring. If the eye has had previous ocular surgery (including prior trabeculectomy, cataract surgery, tube shunt, or trauma), use 66172. If no prior surgery and no scarring, use 66170. When documentation is ambiguous, query the surgeon.
66183 (Ex-PRESS shunt) is mutually exclusive with 66170/66172 per NCCI edits — report 66183 only when a device is implanted.
Trabeculectomy carries a 90-day global period — E/M visits during that period for related care are not separately billable.
Laterality modifiers are required: RT (right eye), LT (left eye). Do not use modifier 50 for bilateral glaucoma surgery — the two eyes are never performed simultaneously.
Common modifiers: 58 (staged/related procedure during global); 78 (unplanned return to OR, related, during global); 79 (unrelated procedure during global); 22 (increased procedural services — e.g., extensive scarring requiring greater work, with supporting documentation); 54/55 (split surgical/postoperative care).
For MIGS procedures (iStent, XEN Gel stent, Kahook Dual Blade), do not substitute 66170/66172 — these have their own specific CPT codes.
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