Trabeculotome Tunneling Trabeculoplasty (3T): A Step-by-Step Surgical Protocol for Primary Open-angle Glaucoma

Summary

This protocol describes Trabeculotome Tunneling Trabeculoplasty (3T)—a minimally invasive glaucoma surgery that includes trabecular incision, Schlemm’s canal (SC) dilation, and tension suture implantation to restore physiological aqueous outflow—accompanied by a noncomparative case series.

Abstract

Primary open-angle glaucoma (POAG) requires sustained intraocular pressure (IOP) reduction to delay disease progression. Traditional filtering surgeries, while effective, are associated with significant tissue trauma, postoperative complications, and long-term scarring. Minimally invasive glaucoma surgery (MIGS) offers a safer alternative but may be limited by incomplete IOP reduction or long-term structural instability of Schlemm’s canal (SC).

Trabeculotome tunneling trabeculoplasty (3T) is a novel MIGS technique designed to restore physiological aqueous outflow while preserving trabecular meshwork (TM) structure. The procedure consists of three key steps: trabecular fenestration using a trabeculotome, viscoelastic-mediated dilation of SC, and placement of a tension suture to maintain long-term canal patency. This article provides a step-by-step surgical protocol and accompanying training video for the 3T procedure. Representative outcomes from a single-center, non-comparative case series demonstrate that 3T is associated with significant IOP reduction, decreased dependence on antiglaucoma medications, and a low complication rate. This protocol aims to facilitate standardized clinical implementation of 3T and provide a practical educational resource for surgeons performing minimally invasive glaucoma procedures.

Introduction

Glaucoma is the leading cause of irreversible blindness worldwide, with POAG being the most common subtype. The 3T procedure is based on the mechanobiological pump theory of the trabecular meshwork (TM), which describes the TM as a biomechanical structure responsive to its mechanical microenvironment¹. The structural and functional integrity of this system is maintained by the biological properties of TM cells and tissues². Preliminary findings from a single-center case series indicate that 3T is associated with significant IOP reduction, reduced medication dependence, and a low complication rate³. Elevated IOP remains the only modifiable risk factor for disease progression⁴. Although trabeculectomy has long been the surgical gold standard for POAG, its limitations—including significant tissue trauma, high complication rates, and long-term scarring risk—have driven the search for safer alternatives^5,6.

MIGS offers a safer option by restoring physiological aqueous outflow with minimal tissue disruption. However, existing MIGS techniques have distinct limitations. GATT effectively lowers IOP but requires circumferential TM incision, leading to considerable TM damage and relatively high rates of hyphema and inflammation^7,8. In contrast, CP and ABiC preserve TM architecture but achieve only modest IOP reduction due to limited outflow expansion, and carry a risk of late SC collapse or reclosure, potentially compromising long-term outcomes⁹.

To address these limitations, the corresponding author, Professor Wang Ningli, developed 3T. The design of 3T is grounded in the mechanobiological pump theory of the TM, which conceptualizes the TM as a biomechanical pump responsive to its mechanical microenvironment¹⁰. The procedure consists of three important steps: (1) trabeculotomy—creating a TM incision to establish an outflow pathway; (2) tunneling—dilating SC with viscoelastic material; and (3) trabeculoplasty—placing a tension suture within SC to provide sustained support.

The tension suture is expected to improve outcomes through two mechanisms: (a) physically maintaining SC patency and preventing late collapse; and (b) generating mechanical tension that may enhance TM cellular activity via mechanobiological pathways, thereby may help preserve TM biomechanical pump function¹¹. Compared with GATT, 3T achieves more confined TM disruption, potentially reducing bleeding and inflammation. Compared with ABiC, the tension suture offers a durable solution to prevent SC collapse.

Based on its design, 3T is suitable for POAG patients requiring IOP reduction while preserving TM structure, and for those undergoing combined cataract surgery—as the procedure can be seamlessly integrated with cataract extraction. This article provides a step-by-step surgical protocol and a dedicated training video for the 3T procedure, aiming to facilitate standardized clinical implementation and serve as a comprehensive educational resource for clinicians.

Protocol

This protocol received approval from the Ethics Committee of Chengdu Integrated TCM & Western Medicine Hospital (2024.XJS.005). Clinical trial registration has been completed; the registration number is: ChiCTR2500099671. Prior to video production for educational purposes, informed consent was obtained from all patients.

1. Inclusion criteria

1. Use the following inclusion criteria: aged 18–75 years (inclusive) at informed consent signing, all sexes; POAG with IOP > 21 mmHg despite maximal tolerated medical therapy, indicating surgical indication; no prior glaucoma surgery or prior ocular surgery with confirmed intact SC via gonioscopy/imaging (UBM/AS-OCT). Acceptable procedures include SLT and subconjunctival implant removal; confirm willingness to undergo surgery and complete all preoperative and postoperative examinations.

2. Exclusion criteria

1. Exclude patients with corneal opacity or structural angle abnormalities that prevent clear gonioscopic visualization or safe surgical manipulation; a history of ocular trauma or surgery that may compromise SC integrity, unless imaging (UBM/AS-OCT) confirms the canal is patent and structurally intact; prior GATT/iStent implantation/trabeculectomy unless imaging confirms canal integrity; end-stage glaucoma or advanced glaucoma poorly controlled despite maximal medical therapy; contraindications such as conditions affecting intraocular pressure (e.g., thyroid eye disease, uveitis); comorbidities impairing visual fields (e.g., neurological disorders, intracranial tumors); severe cardiopulmonary disease or advanced malignancy; incomplete preoperative or postoperative examinations, pregnancy or lactation, or other criteria deemed by the investigator to preclude enrollment.

3. Preoperative preparation

1. Confirm patient identity and obtain written informed consent. Perform routine preoperative assessments, including anthropometric measurements (height, weight), vital signs (body temperature, blood pressure), and random blood glucose monitoring.
2. Perform laboratory evaluation, including hematologic parameters (complete blood count), biochemical profile (liver and renal function tests), and infectious disease screening (hepatitis B serology, coagulation studies, and inflammatory markers). Perform lacrimal duct irrigation to exclude occult ocular surface infections.
3. Mark the operative eye using standardized surgical site marking protocols to prevent wrong-site procedures.

4. Operative technique of the 3T procedure

1. Administer pilocarpine eye drops 3x at 10 min intervals 30 min preoperatively to constrict the pupil.
2. Administer general anesthesia. If administering local anesthesia, administer peribulbar plus topical anesthesia; if inadequate, supplement with intracameral 1% lidocaine (0.1–0.2 mL diluted 1:1). Exercise caution with retrobulbar blocks in glaucoma patients due to blindness risk.
3. Use a surgical marker to indicate corneal limbus clock hours: right eye 3–7 o'clock, left eye 6–10 o'clock. Stain the scalpel blade for clear identification of incision sites.
4. Trim one strand of 10-0 polypropylene IOL suture to 12 cm length, retaining the curved needle.
5. Stand at the temporal side or superior-temporal position relative to the patient. Tilt the microscope 30–45° outward relative to the eye, with the patient's head tilted nasally/inferiorly (adjustable before microcatheter insertion).
6. Intraoperative guidance for catheter placement and suture tension
   1. Consider the catheter correctly positioned once it enters the SC if under gonioscopy, proper entry into the SC is clearly visualized, which is the same as the catheter manipulation in the GATT procedure.
   2. The tip of the microcatheter has a marker whose position is visible as the microcatheter advances through the SC. If resistance is encountered during advancement (indicating SC blockage), stop advancement, withdraw the microcatheter, and attempt advancement in the opposite direction through the trabecular meshwork incision.
   3. Look for tactile and visual cues for blockage: when SC blockage occurs during cannulation, resistance is distinctly felt, and the tip marker of the microcatheter will not move.
   4. Target suture tension is a relative quantitative concept. Before knotting, shallow the anterior chamber and lower IOP; when tying the knot, gently tighten the suture. After the anterior chamber is reformed and IOP is restored, the suture acquires a certain degree of tension and may move with the trabecular pump function. The final successful configuration is achieved when the knot is positioned above Schwalbe’s line (SW) and the suture lies within the SC lumen.
7. Maintaining anterior chamber stability
   1. Use an appropriate amount of viscoelastic to maintain chamber depth and prevent collapse or Descemet’s membrane detachment.
   2. In case of hyphema obscuring the view, inject diluted epinephrine (1:10) into the anterior chamber for hemostasis, followed by irrigation to restore clarity.
   3. Ensure a clear cornea, open angle, and constricted pupil (with pilocarpine pretreatment) for optimal gonioscopic visualization of the trabecular meshwork and Schlemm’s canal.
   4. In combined procedures, adjust the microscope angle and gonio lens position after lens extraction to optimize angle visualization, as the anterior chamber may deepen.

5. Key operative steps (see Figure 1)

1. Make an auxiliary 15° knife incision at the inferotemporal limbus (right eye) or superonasal limbus (left eye) with viscoelastic injection to elevate IOP to approximately 30 mmHg, followed by a 1.8 mm clear corneal main incision at the superotemporal or temporal limbus.
2. Preload the microcatheter at the auxiliary incision site.
3. Create a 2 mm incision through the inferonasal or nasal TM and inner wall of SC using a trabecular blade.
4. Dilate the incision site with viscoelastic to maintain patency and facilitate microcatheter passage. If reflux occurs, use viscoelastic to displace it and facilitate microcatheter insertion.
5. Insert the microcatheter tip counterclockwise into SC, with viscoelastic administered every 2–3 clock positions for canal dilation. After circumnavigating 360°, advance the catheter approximately 1 clock position beyond the incision site, outside SC, to facilitate externalization.
6. Create a secondary auxiliary incision and externalize the catheter tip (~2 mm). Ligate a 10-0 curved polypropylene suture 1–2 mm from the tip with double knots; avoid triple knots to prevent SC trauma.
7. Retract the sutured microcatheter tip into the anterior chamber and draw the suture into SC while administering viscoelastic every 2–3 clock positions. Continue until the catheter completes 360° retraction and exits the eye with 3–5 mm of external suture, then cut the ligation site.
8. Enlarge the fenestration site with viscoelastic under gonioscopy (~60° opening).
9. Insert the curved suture needle into the anterior chamber, thread it beneath the opposite suture end, and exit via the corneal limbus. Avoid threading above the opposite suture end to prevent suture entanglement.
10. Reinsert the curved suture needle through the corneal limbus and pass it superficially along the limbal trajectory.
11. Insert the curved needle through an auxiliary incision into the anterior chamber and exit through the corneal limbus. Leave approximately 10 mm of suture externally before trimming excess.
12. Hook both suture ends through the auxiliary incision.
13. Irrigate the anterior chamber with viscoelastic partially to lower IOP.
14. Perform surgical knotting (three ties) and trim the suture.
15. Irrigate the anterior chamber, adjust the knot to the angle, hydrate the corneal incision, and restore the chamber. Inject gas to slightly elevate IOP and conclude the procedure.

6. Combined cataract surgery with 3T

NOTE: Complete cataract surgery prior to initiating 3T surgery. Use the same primary incision for both cataract surgery and 3T. The 3T procedure itself is not modified when combined with cataract surgery.

1. Create a micro-incision measuring 1.8–2.2 mm.
   NOTE: Maintain incision size to preserve chamber depth and avoid complications.
2. Implant the intraocular lens.
3. Remove viscoelastic material from the capsular bag.
4. Constrict the pupil.
5. Re-inject viscoelastic into the anterior chamber.
6. Proceed with the 3T surgical steps.

7. Management of major surgical complications

1. Hemorrhage
   1. If bleeding is minimal and does not obscure the view, continue surgery. If significant bleeding occurs, inject diluted epinephrine (1:10), irrigate, inject viscoelastic, and repeat if necessary.
2. Microcatheter obstruction
   1. If obstruction is encountered, withdraw the catheter, change direction, and re-enter. If obstruction persists, convert to GATT.
3. SC tearing
   1. If tear is <150°, continue the procedure. If ≥150°, consider conversion.
4. Postoperative IOP spike
   1. IOP spike usually occurs within the first postoperative week but may appear up to one month after surgery and is defined as IOP ≥30 mmHg. Discontinue steroid eye drops and add topical IOP-lowering agents. If IOP remains >30 mmHg, consider oral carbonic anhydrase inhibitors. If IOP >40 mmHg, perform anterior chamber paracentesis.
      NOTE: Most cases normalize within a few days.

8. Postoperative medication protocol

1. Administer antibiotic eye drops 4x daily for 4 weeks.
2. Administer NSAID eye drops for 3 months.
   NOTE: This represents institutional preference; shorter courses or alternatives may be used.
3. Administer prednisolone acetate eye drops for 1 week.
   NOTE: Discontinue if IOP rebound occurs.
4. Initiate pilocarpine eye drops 1 week postoperatively (3x daily for 3 months).
   NOTE: This represents institutional preference; shorter duration or omission may be considered.

Results

Study population and case distribution
Between December 2022 and September 2023, a single surgical team at Chengdu Integrated TCM & Western Medicine Hospital performed the 3T procedure on 42 patients (42 eyes) with POAG in this retrospective study. Consecutive patients meeting the inclusion criteria during the study period were enrolled without selection bias. All included cases underwent standalone 3T surgery; no combined cataract surgery cases were enrolled in this study. All surgeries were per...

Discussion

The increased resistance to aqueous humor outflow in primary POAG arises primarily from microstructural alterations in the TM and SC, including excessive extracellular matrix deposition leading to tissue stiffness, SC collapse, and impaired biomechanical pumping function of the TM^14,15,16. In response to these pathomechanisms, the corresponding author developed the 3T procedure—a minimally invasive technique that reconstru...

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Blunt hook threader	Suzhou Mingren Medical Instruments Co., Ltd.	MR-S600
Corneal scissors	Suzhou Mingren Medical Instruments Co., Ltd.	MR-V220
Double-mirror gonioprism	Volk Optical Inc.	G-2
Intraocular forceps	Suzhou Mingren Medical Instruments Co., Ltd.	MR-E315
Lens implantation forceps	Suzhou Mingren Medical Instruments Co., Ltd.	MR-I310
Lens manipulator hook	Suzhou Mingren Medical Instruments Co., Ltd.	MR-S520
Micro-capsulorhexis forceps (curved tip)	Suzhou Mingren Medical Instruments Co., Ltd.	MR-C140
Microcatheter	US New Sight Medical Co., Ltd. / Tianjin USIGHTS Ophthalmic Technology Co., Ltd.	iTRACK 250A / USIGHTS UC100
Micro-conjunctival scissors	Suzhou Mingren Medical Instruments Co., Ltd.	MR-V250
Micro-locking forceps	Suzhou Mingren Medical Instruments Co., Ltd.	MR-E161S
Micro-needle holder	Suzhou Mingren Medical Instruments Co., Ltd.	MR-N420
Micro-platform forceps	Suzhou Mingren Medical Instruments Co., Ltd.	MR-E160
Micro-toothed forceps	Suzhou Mingren Medical Instruments Co., Ltd.	MR-E140
Ophthalmic ruler	Suzhou Mingren Medical Instruments Co., Ltd.	MR-M100
Single-mirror gonioprism	Volk Optical Inc.	G-1 (VG1)
Thread fork	Suzhou Mingren Medical Instruments Co., Ltd.	MR-C810
Vannas scissors	Suzhou Mingren Medical Instruments Co., Ltd.	MR-V295
Zeng’s Trabeculotomy Knife	Bier Feng (now Bili Medical Group)	IF-8006D4