Navigating the Angles: A Retrospective Analysis of One-year Outcomes of Gonioscopy-assisted Transluminal Trabeculotomy in Primary Open-angle Glaucoma

Summary

Gonioscopy-assisted transluminal trabeculotomy significantly reduces intraocular pressure and medication in patients with primary open-angle glaucoma. Postoperative angle changes include forward iris insertion, narrowing angle width, pigment reduction and accumulation, and frequent PAS formation, predominantly in the nasal quadrant. These effects remain stable through the 12-month follow-up.

Abstract

This study aimed to evaluate postoperative angle changes following gonioscopy-assisted transluminal trabeculotomy (GATT) in patients with primary open-angle glaucoma (POAG) over 1 year of follow-up. We conducted a retrospective analysis of 60 eyes from 41 POAG patients who underwent GATT, assessing intraocular pressure (IOP), number of ocular hypotensive medications, and gonioscopic findings preoperatively and at 3, 6, and 12 months postoperatively using the Spaeth classification. Postoperative IOP and medication use were significantly reduced throughout follow-up. Gonioscopic examination revealed forward movement of the iris root insertion in all quadrants, most notably inferiorly, with angle width narrowing up to 10°, primarily in the nasal quadrant. Overall pigment angle decreased initially, then gradually increased, with the nasal quadrant showing the highest pigment levels; the pigment pattern changed from diffuse preoperatively to stacked postoperatively. Peripheral anterior synechia (PAS) developed in 39 eyes (65%) and stabilized by 3 months, with the nasal quadrant most affected and showing a gradually increasing extent of involvement. Regarding the trabeculotomy cleft, 28 eyes (46.7%) maintained a widely patent opening, 29 (48.3%) showed a narrow opening, and 3 (5%) were completely closed. Angle rebleeding sites varied among patients, occurring most frequently in the nasal quadrant. In conclusion, GATT significantly reduced IOP and medication use over 12 months, with characteristic angle changes including forward iris insertion, narrowing angle width, altered pigment distribution with accumulation, predominant PAS formation in the nasal quadrant, and variable rebleeding sites.

Introduction

Primary open-angle glaucoma (POAG) is characterized by progressive optic neuropathy driven primarily by elevated intraocular pressure (IOP) due to impaired aqueous humor outflow through the trabecular meshwork (TM)-Schlemm's canal pathway^1,2. While traditional filtering surgeries create alternative drainage pathways, they are associated with significant complications and bleb-related morbidity. Gonioscopy-assisted transluminal trabeculotomy (GATT), an ab interno circumferential trabeculotomy, has emerged as a minimally invasive alternative that targets the pathological resistance directly by incising the TM to restore physiological outflow^3,4. Unlike trabeculectomy, GATT preserves the conjunctiva and scleral wall, offering reduced tissue trauma and faster recovery⁵. However, the long-term efficacy of GATT depends on the patency of the created outflow channel, which is influenced by postoperative wound healing and tissue remodeling.

Despite established IOP-lowering efficacy^6,7, the anatomical evolution of the anterior chamber angle following GATT remains inadequately characterized. Existing literature has focused primarily on IOP outcomes and complication rates, while systematic evaluation of angle morphology changes—specifically the temporal dynamics of peripheral anterior synechia (PAS) formation, iris root position changes, angle width modifications, pigment redistribution, and incision patency patterns—is notably lacking. Critical knowledge gaps persist regarding: (i) the chronological sequence of angle structural remodeling during the first postoperative year; (ii) the quadrant-specific patterns of tissue healing (particularly the predisposition for PAS development and iris insertion advancement in specific sectors); and (iii) the relationship between progressive angle closure (including the transition from deep to shallow incision opening or complete closure) and sustained IOP control. Understanding these structural dynamics is essential for elucidating the mechanisms underlying GATT's long-term efficacy and identifying anatomical predictors of surgical success.

We hypothesized that post-GATT angle morphology follows a characteristic temporal evolution pattern involving sequential anatomical remodeling: initial TM incision creates a circumferential outflow channel that subsequently undergoes progressive modification through wound healing responses. Specifically, we anticipated forward movement of the iris root insertion (predominantly in the inferior quadrant), progressive narrowing of the angle width (most pronounced nasally), and development of PAS, with a quadrant-specific predilection for the nasal sector, stabilizing by 3 months postoperatively. Despite partial closure of the surgical incision—transitioning from deep opening to shallow opening or complete closure—and progressive PAS formation, sufficient aqueous outflow pathways remain functional to sustain IOP reduction throughout the 12-month follow-up period.

This investigation addresses these knowledge gaps and offers novel contributions to the MIGS literature. First, by establishing the temporal sequence of angle remodeling, we provide anatomical validation that GATT achieves sustained IOP control despite partial anatomic closure, challenging the assumption that complete 360° TM patency is required for long-term success⁸. Second, our quadrant-specific analysis of iris insertion position, PAS distribution (with particular attention to nasal quadrant involvement), and rebleeding patterns offers mechanistic insights into postoperative wound healing dynamics and sectoral outflow resistance changes. Third, correlation of intraoperative gonioscopic findings with postoperative structural outcomes identifies critical technical refinement targets—such as optimizing incision depth in quadrants prone to PAS formation—to enhance procedural consistency and 360° incision completion rates. Finally, by delineating the relationship between early postoperative angle characteristics (incision depth grading and PAS extent at 3 months) and long-term IOP control, this study establishes predictive morphological biomarkers that enable clinicians to stratify patients and tailor follow-up strategies based on individual angle remodeling patterns. Collectively, these findings advance our understanding of angle-based surgery mechanisms and provide evidence-based guidance for optimizing patient selection, surgical technique, and postoperative management.

Protocol

Study design
All research procedures involving human participants were conducted in accordance with the Declaration of Helsinki and approved by the Institutional Review Board (IRB) of Chengdu First People's Hospital (Approval ID: CDFPR-2024-GATT-018)⁹. Written informed consent was obtained from all participants prior to enrollment, detailing the surgical procedure, potential risks, and longitudinal follow-up requirements. The study employs a retrospective cohort design with standardized data collection protocols implemented in November 2018, enabling analysis of consecutive patients through November 2023.

Methods
Data from patients undergoing GATT operations at Chengdu First People's Hospital were collected. The study follows the principles laid down in the Declaration of Helsinki¹⁰. All patients were examined at corresponding points before and after surgery, and the relevant observation indicators were recorded.

Patients
The inclusion criteria for this study consisted of patients diagnosed with POAG who required GATT surgery due to uncontrolled IOP despite maximal medical therapy (18 years of age or older). Additionally, patients who were intolerant to glaucoma medication (due to nonadherence or ocular allergy) and those with evidence of progressive glaucoma as determined by visual field examination were included.

The exclusion criteria for this study were as follows: age younger than 18 years, previous ocular surgery or trauma, presence of combined ophthalmologic diseases other than POAG (such as uveitis, cataract, ectopia lentis, aniridia, axial myopia, etc.), presence of PAS as assessed by preoperative microscopy, and irregular follow-up of less than 1 year.

During the preoperative evaluation, detailed ophthalmic examinations were conducted, including assessment of best-corrected visual acuity (BCVA) using a standard Snellen chart, slit-lamp biomicroscopy, gonioscopy, and IOP measurement. Central 24-2 threshold visual field tests were performed using the SITA-Fast strategy with the Humphrey Field OCT. Retinal nerve fiber analysis was conducted using spectral domain optical coherence tomography.

Surgical procedure
All operations were performed by the same experienced ophthalmologist. After standard aseptic disinfection, the operated eye was covered, and the eyelid was fixed with an eyelid retractor. Topical anesthesia was applied to the operated eye. A primary incision was made first at the temporal limbus, and an auxiliary incision directed toward the nasal angle was made superiorly or inferiorly. Lidocaine stock solution, miotic, and high cohesive viscoelastic were injected into the anterior chamber to increase intraocular pressure (approximately 30 mm Hg). This was done to maintain anterior chamber depth and prevent bleeding. Under direct gonioscopy, a goniotomy ranging from 1 to 2 h was performed in the nasal angle with a 25 G microknife to expose the Schlemm's lumen. Then, the microcatheter with a light source is introduced into the anterior chamber through the auxiliary incision and into the Schlemm lumen at an angle of 10–15° under direct gonioscopy, slowly advancing around the lumen for 360°. The right eye is usually counterclockwise, and the left eye is clockwise. In case of resistance, it needs to be retracted and adjusted or another incision is reverse encircled; when the suture or catheter tip is punctured out from the goniotomy, the two ends of the head and tail are clamped with microforceps to pull outwards to form the lasso and tighten, the trabecular meshwork and the inner wall of Schlemm's canal are torn to complete 360 trabeculotomy, and blood reflux from the superficial scleral vein is observed at this time; finally, the device is withdrawn, perfusion aspiration is performed to remove part of the viscoelastic agent but 15%-40% is retained to fill the hemostasis, and the intraocular pressure is adjusted to the first day after surgery target of 15–18 mmHg. Antibiotics, glucocorticoids, and pilocarpine eye drops are routinely used after surgery. Examinations were performed on the first day, the first week, the first month, the third month, the sixth month, and the first year after surgery. Anterior chamber microscopy, intraocular pressure, and use of antiglaucoma medications were recorded at each follow-up visit.

Standard for successful surgery
The success of GATT surgery is divided into two levels¹¹: complete success (without the need for medication, with intraocular pressure ranging from 6 to 18 mmHg and a reduction of ≥20–30% compared to the baseline) and conditional success (achieved with ≤2 types of medication to reach the same intraocular pressure target). Failure is defined as uncontrolled intraocular pressure, the need for another surgery, or the occurrence of serious complications. This study was followed up for 1 year after surgery, and no failures were observed.

Assessment of postoperative PAS formation
Angle morphology was observed and recorded preoperatively, as well as at 3 months, 6 months, and 1 year postoperatively. Following routine ophthalmic examinations, each patient's angle characteristics were assessed using a four-sided gonioscope. To ensure patient comfort, topical anesthetic eye drops (0.5% proparacaine hydrochloride) were instilled on the ocular surface. Levofloxacin gel was then applied to fill the lens concavity. Carefully touching the patient's cornea, the lens was rotated to maintain the eye in the main position. Slit lamp examination and the Spaeth method were employed to observe and record the patient's angle characteristics. Figure 1 provides a representative image of PAS evaluation in this study.

Statistical analysis
All data from participants were analyzed. Non-normal distribution data were presented as median and interquartile range, and grade data and categorical data were presented as frequency and percentage. For the categorical and ordinal data derived from the Spaeth classification (including iris root insertion grade, angle width, and pigment grading) evaluated across multiple time points (preoperatively and at 3, 6, and 12 months postoperatively), the Friedman test was used for overall comparison. When the Friedman test indicated a statistically significant difference, post hoc pairwise comparisons between specific time points were conducted using the Wilcoxon signed-rank test, with a Bonferroni correction to adjust the P-value threshold for multiple comparisons. For repeated-measures binary data (e.g., the presence or absence of specific complications over time), Cochran's Q test was used. All statistical analyses were two-sided, and a P-value < 0.05 (or the Bonferroni-adjusted P-value for post-hoc tests) was considered statistically significant¹².

Results

This retrospective study analyzed gonioscopic data from 60 eyes of 41 patients with POAG, comprising 36 male eyes (60%) and 24 female eyes (40%), with a mean age of 51.8 ± 15.4 years. Following GATT, both IOP and the number of ocular hypotensive medications were significantly reduced compared to baseline (both P < 0.001; Table 1). Significant morphological alterations in the angle structure were observed postoperatively when comparing preoperative and 1-year follow-up gonioscopic findings (

Discussion

This study demonstrates that GATT effectively lowers IOP and reduces medication dependence in POAG patients by restoring physiological aqueous humor drainage through trabecular meshwork incision. Our serial gonioscopic observations revealed characteristic postoperative anatomical changes: anterior displacement of the iris root insertion, overall angle narrowing, fluctuating angle pigmentation, and progressive peripheral anterior synechiae (PAS) formation predominantly in the nasal quadrant. It is important to note that w...

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Anterior segment OCT system (RTVue 100-2)	Optovue	Retinal nerve fiber layer analysis
Balanced salt solution / irrigation solution	Alcon (BSS)	Anterior chamber irrigation
Carbamazepine retractor / iris retractor	ASICO	Used during surgical exposure
Diclofenac sodium ophthalmic solution	Novartis	Postoperative NSAID
Eyelid speculum	Rhein Medical	Maintains eyelid opening during surgery
Four-mirror gonioscopy lens	Volk	Angle visualization
Humphrey Field Analyzer HFA-750i	Carl Zeiss Meditec	Visual field testing
Illuminated microcatheter for trabeculotomy	Ellex	360° canalization of Schlemm's canal
Levofloxacin ophthalmic solution	Santen Pharmaceutical	Postoperative antibiotic
Microforceps	DORC	Manipulation of catheter and tissue
Microknife 25G	Alcon	Goniotomy incision
Pilocarpine ophthalmic drops	Novartis	Postoperative miotic
Prednisolone acetate ophthalmic suspension (Pred Forte)	Allergan	Topical corticosteroid
Proparacaine hydrochloride 0.5% ophthalmic solution	Bausch & Lomb	Topical anesthetic
SPSS Statistics 25.0	IBM	Statistical analysis software
Slit-lamp biomicroscope	Zeiss	Anterior segment examination
Snellen visual acuity chart	Precision Vision	Visual acuity testing
Viscoelastic ophthalmic surgical device	Bausch & Lomb	Maintains anterior chamber depth during surgery