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Five-year outcomes of trabeculo-canalectomy for Chinese PACG patients: a retrospective study

BMC Ophthalmology volume 25, Article number: 234 (2025) Cite this article

Abstract

Background

To evaluate the 5-year outcomes of trabeculo-canalectomy in the treatment of primary angle-closure glaucoma (PACG) among Chinese patients.

Methods

A retrospective study was designed, involving 46 PACG patients (50 eyes) treated with trabeculo-canalectomy at the First Affiliated Hospital of Nanjing Medical University from January 2016 to December 2018. The patients were followed up at 1 week, 1 month, 3 months, 6 months, 12 months, 1 year, 2 years and 5 years. Surgical success was defined as intraocular pressure (IOP) ≤ 21 mmHg (1 mmHg = 0.133 kPa) under glaucoma medication (qualified success) and without any glaucoma medication (absolute success). Main outcomes were measured according to IOP, number of medication regimens, surgical success rate, complications, and filtering bleb status.

Results

A total of 46 PACG patients (50 eyes) were finally included for statistical analysis, with a mean age of 56.68 ± 6.75 years (range, 41–69 years). The mean preoperative IOP was 30.72 ± 10.26 mmHg with a median number of medication regimens of 2 (range, 0 to 4). Compared to those before the operation, the mean IOP decreased to 12.15 ± 3.11, 14.33 ± 4.10, 15.68 ± 4.24, 16.45 ± 4.14, 16.95 ± 3.51, 17.67 ± 3.15 and 17.04 ± 3.78 mmHg at 1 week, 1 month, 3 months, 6 months, 12 months, 1 year, 2 years and 5 years, respectively. The median (range) numbers of medication regimens were 0 (0 ~ 1), 0 (0 ~ 2), 0 (0 ~ 2), 0 (0 ~ 2), 0 (0 ~ 2), 0 (0 ~ 3), 0 (0 ~ 3), 0 (0 ~ 3) at the eight time points, respectively. The mean postoperative IOP and the number of medication regimens at each time point were significantly lower than those before operation (all P < 0.01). The 5-year total success rate was 89%, and the absolute success rate was 78%. Shallow anterior chamber (10%) and hyphema (12%) were the most common complications early after surgery. At 3 months, anterior segment slit-lamp photography and ultrasound biomicroscopy showed no obvious filtering blebs in 50 eyes (100%). IOP increased transiently in 6 eyes (12%) within 1 month after surgery.

Conclusion

Simple and cost-saving trabeculo-canalectomy provides favorable 5-year outcomes in the treatment of medically uncontrolled PACG, as shown by more effective IOP control, more obvious drug reduction, as well as fewer post-operative interventions compared to trabeculectomy.

Peer Review reports

Background

Primary angle-closure glaucoma (PACG), a major subtype of glaucoma, accounts for 50% of all glaucoma-related cases of blindness worldwide [1, 2]. The number of PACG patients is estimated to reach 32.04 million by 2040 globally, three quarters of which occur in Asia [3, 4], indicating that PACG has become a worldwide public health burden [5, 6].

Given that PACG arises from anatomical derangement of the anterior segment, all treatment strategies aim at repairing anatomical defects and reducing intraocular pressure (IOP) [4]. Cataract surgery with or without trabeculectomy (Trab) is advocated as the initial treatment for PACG patients with younger ages, clear lens and diffused peripheral anterior synechiae (> 180 degrees) [1, 7,8,9]. However, its efficacy is significantly reduced by excessively low or high filtration that inevitably leads to hypotony, shallow anterior chamber, scars, and other complications [10]. Therefore, Trab should be modified to improve efficacy and reduce complications in the treatment of glaucoma.

Trab was first proposed by Cairns [11]. In about two-thirds of Cairns’ cases, IOP can be continuously controlled without subconjunctival drainage to aqueous humor [12]. As suggested by Carins, this surgical technique can reduce IOP in chronic simple glaucoma by relieving trabecular obstruction without intentionally creating external drainage. Cairns lays out a rationale for us to design trabeculo-canalectomy [14]. In PACG patients, the anterior chamber angle is blocked by anatomical alterations, thus impeding the aqueous humor flowing through [9, 13] while the post-trabecular outflow pathway may remain intact [9, 14, 15]. A direct communication between the anterior chamber and the Schlemm’s canal can restore aqueous humor outflow in PACG patients [9]. Thus, it is theoretically possible to re-establish this communication for reducing IOP independent of a filtration bleb.

Herein, we modified Trab into trabeculo-canalectomy, by draining the aqueous humor from the cut end of Schlemm’s canal to re-establish good IOP control, without dependence on a filtration bleb and preventing post-surgery scarring. We evaluated its 5-year clinical outcomes in treating medically uncontrolled PACG eyes.

Materials and methods

Study population

Enrolled were 60 patients (70 eyes) treated with trabeculo-canalectomy in the First Affiliated Hospital of Nanjing Medical University, China, from January 2016 to December 2018. Of them, 14 patients (20 eyes, 28.57%) were excluded due to a follow-up of < 3 months. Finally, 46 patients (50 eyes) were included.

Inclusion criteria

Inclusion criteria included.

  1. (1)

    Ages 40 years or above;

  2. (2)

    Medically uncontrolled PACG and peripheral anterior synechiae of more than 180°;

  3. (3)

    Uncontrolled PACG defined as IOP > 21 mmHg for at least three consecutive measurements within previous one month, and on two or more glaucoma medications in the presence of glaucomatous optic disc neuropathy and visual field deficiency;

  4. (4)

    Best corrected visual acuity (LogMAR) ≤ 0.3 without obvious lens opacity.

Exclusion criteria

Exclusion criteria included.

  1. (1)

    Primary open angle glaucoma, neovascular glaucoma, normal tension glaucoma, traumatic glaucoma, and secondary glaucoma;

  2. (2)

    Other histories of fundus disease and eye surgery (except for laser periphery iridotomy or iridoplasty);

  3. (3)

    Signs of suprascleral venous hypertension (e.g., torturous and dilated suprascleral veins);

  4. (4)

    Severe heart, lung disease, and advanced cancer;

  5. (5)

    A history of mental illness;

  6. (6)

    Previous treatment with anticoagulant therapy and kidney dialysis or pregnancy;

  7. (7)

    No informed consent;

  8. (8)

    Incapability to adhere to the follow-up schedule required by this study.

Surgical procedures

All surgeries were performed by one designated experienced surgeon at the First Affiliated Hospital of Nanjing Medical University. 2.5 mL of 2% lidocaine + 0.75% bupivacaine (mixed in a ratio of 1:1) was applied for peribulbar anesthesia. A suspension wire was made of 8 − 0 absorbable suture in the corneal limbus. A fornix-based incision through the conjunctiva and Tenon’s capsule was made. Then, a 4 × 4 mm superficial scleral flap in 1/2 scleral thickness was sculpted (Fig. 1a). Schlemm’s canal was located (Fig. 1b), its outer wall opened (Fig. 1c-d), and then this wall and the trabecular meshwork measuring 1 × 2 mm removed (Fig. 1e). Following resection of the peripheral iris at 12 o’clock (Fig. 1f), moderate viscoelastic agents were injected under the scleral flap to reinsert the iris (Fig. 1g). The scleral flap was closed tightly with two sutures of 10 − 0 nylon (Fig. 1h). The conjunctiva-Tenon’s layer was sutured with 10 − 0 nylon at the ends of the incision (Fig. 1i). The corneal side port incisions were hydrated and made watertight. Antimetabolic agents such as mitomycin C or 5- fluorouracil were not used intraoperatively.

Fig. 1
figure 1

Trabeculo-canalectomy procedures. a Dissecting a rectangular superficial scleral flap of 4 × 4 mm and in 1/2 scleral thickness at the superior limbus into the transparent cornea. b Locating Schlemm’s canal. Black arrows indicate the broken end of Schlemm’s canal. c Inserting the corneal scissors into the broken end of Schlemm’s canal. d Opening the outer wall of Schlemm’s canal. Black arrows indicate the unroofed Schlemm’s canal. e Removing the outer wall of Schlemm’s canal and the juxtacanalicular trabecular meshwork. f Peripheral iridectomy. g Injecting moderate viscoelastic agents under the scleral flap to reinsert the iris. h Closing the scleral flap tightly with two sutures of 10 − 0 nylon. i Suturing the conjunctiva-Tenon’s layer with 10 − 0 nylon at the end of the incision

Full size image

Observational indexes

Postoperative follow-up was made at 1 week, 1 month, 3 months, 6 months, 12 months, 1 year, 2 years and 5 years, with additional visits whenever necessary, for documentation of IOP, number of anti-glaucoma regimens, best corrected visual acuity (BCVA), results of anterior and posterior segment examination, frequency of complications, postoperative interventions and morphology of filtering blebs.

Evaluation of surgical success or failure

Evaluation of surgical success or failure included [16]

  1. (1)

    Complete success: post-operative IOP at 6 to 21 mmHg without anti-glaucoma medications;

  2. (2)

    Conditional success: post-operative IOP at 6 to 21 mmHg with local application of anti-glaucoma medications;

  3. (3)

    Failure: post-operative IOP lower than 6 mmHg or higher than 21 mmHg after application of anti-glaucoma medications. In these cases, severe complications were observed, such as retinal detachment and endophthalmitis.

The extent and height of filtering blebs were graded by Indiana Bleb Appearance Grading Scale (IBAGS) [17]. Bleb height referred to the vertical dimension of the filtering bleb and represented the elevation of the conjunctival flap above the scleral surface. The height of the bleb was divided into four levels: H0, flat without visible elevation; H1, slight elevation; H2, moderate elevation; and H3, significant elevation as compared with the standard images. Bleb extent represented the horizontal dimension of the filtering bleb, or bleb area. This extent was also divided into four levels: E0, no visible extent (within less than 1 clock); E1, extent between 1 clock and 2 clock hours; E2, extent between 2 clock and 4 clock hours; and E3, extent beyond 4 clock hours.

Statistical analysis

SPSS version 21.0 was used for statistical analyses. Continuous variables were summarized as means, standard deviations, medians, and ranges; categorical variables as frequencies and percentages. Student’s t test was performed for comparison between groups, and one-way ANOVA for comparison among three or more groups. Statistical significance was defined by a P value < 0.05.

Results

A total of 46 PACG patients (50 eyes), including 17 men, were recruited in this study, with a mean age of 56.68 ± 6.75 years (range 41–69 years), an average preoperative IOP of 30.72 ± 10.26 mmHg, and a median (range) number of medication regimens of 2 (0 ~ 4). Patient characteristics are presented in Table 1.

Table 1 The basic data for patient enrollments
Full size table

The mean postoperative IOP decreased from the preoperative 30.72 ± 10.26 to 12.15 ± 3.11, 14.33 ± 4.10, 15.68 ± 4.24, 16.45 ± 4.14, 16.95 ± 3.51, 17.67 ± 3.15 and 17.04 ± 3.78 mmHg at 1 week, 1 month, 3 months, 6 months, 1 year, 2 years and 5 years, respectively (Table 2). The difference between the mean IOP values at baseline and each follow-up point was statistically significant (P < 0.001, Fig. 2). The median (range) numbers of medication regimens were 0 (0 ~ 1), 0 (0 ~ 2), 0 (0 ~ 2), 0 (0 ~ 2), 0 (0 ~ 2), 0 (0 ~ 3), 0 (0 ~ 3) at the seven time points, respectively (Table 2). The difference between the numbers of anti-glaucoma regimens at baseline and each follow-up point was statistically significant (P < 0.001, Table 2). BCVA at post-operative 5 years was 0.23 ± 0.11, and not different from that at baseline (P = 0.388).

Table 2 IOP and medications of the patients completed trabeculo-canalectomy
Full size table
Fig. 2
figure 2

Intraocular pressure values at baseline and seven follow-up time points. IOP values were shown as mean ± SD. SD, standard deviations. IOP, intraocular pressure

Full size image

The total success rate of surgery was 89% at 5 years, including the complete success rate 78% and the conditional success rate 11% (Table 3). According to IBAGS, the filtering bleb in 5 (10%) eyes was graded as E1H1 at 1 week after surgery. Ultrasound biomicroscopy and anterior segment slit-lamp photography showed that 50 eyes (100%) had no obvious filtering bleb (E0H0) at 3 months (Fig. 3). Shallow anterior chamber (10%) and hyphema (12%) were the most common complications early after surgery. IOP elevated in 6 eyes (12%) transiently within 1 month after surgery, and was reduced after topical use of glaucoma medications. No blebitis, hypotony, choroidal detachment, malignant glaucoma and endophthalmitis were observed.

Table 3 Rates of absolute and qualified successes
Full size table
Fig. 3
figure 3

Slit-lamp photographs and ultrasound biomicroscopy images in a patient with PACG at 5 years after trabeculo-canalectomy. a-b Slit-lamp photographs showing the absence of filtration blebs. c Ultrasound biomicroscopy images showing no obvious filtration blebs at the operation site. d Ultrasound biomicroscopy images showing that periphery anterior chamber angle kept closed after the surgery except for the operation site

Full size image

Discussion

Trab is the primary approach to treat glaucoma; however, vision-threatening complications may occur in 39% of Trab-treated cases, 74% of which need urgent postoperative interventions [18]. Moreover, bleb-related complications may persist, regardless of IOP well controlled after surgery [19]. Additionally, scarring in the filtering bleb often leads to treatment failure [17]. Thus, anti-scarring and bleb-independent surgical procedures remain to be developed.

In the present study, we reported the 5-year outcomes of bleb-independent trabeculo-canalectomy, a novel procedure. At five years, trabeculo-canalectomy achieved a total success rate of 89% (Table 3), suggesting its superior therapeutic effects in comparison with previous literatures [20,21,22,23]. Surgical complications mainly occurred within 1 month after surgery, including shallow anterior chamber (10%), hyphema (12%), and transient IOP elevation (12%). A filtering bleb was not needed after trabeculo-canalectomy. This surgery provides a new option for PACG patients.

Trab, initially described by Cairns in 1968 [12], has been considered as the “gold standard” for filtration surgery [24]. Initially, this operation aims to remove the Schlemm’s canal and trabecular meshwork and form a natural pathway for aqueous to egress the eye, in addition to bleb formation. But, later histopathologic examinations recognized that what the surgeons mostly remove was not Schlemm’s canal or trabecular meshwork, but the peripheral cornea, and IOP reduction is mainly due to filtering bleb formation. Then, Trab was modified as an “externo technique” by surgeons. Previous studies have shown that the effect of Trab fails in about 30% cases at 3 years, and nearly 50% at 5 years [22, 23], mainly due to the formation of scar tissue in the conjunctiva, the tenon capsule and the interocular membrane as the natural reaction to wound healing [25].

It is worth noting that trabeculo-canalectomy reported in this study might revolutionize the surgical concept of “external filtration” by reconstructing a physiological drainage channel for the treatment of PACG. It proves an “internal filtration” and bleb-independent procedure that prevents the occurrence of filtration bubble scarring. With the excision of a portion of the Schlemm’ Canal with its trabecular covering, two cut ends were left open into aqueous humor, thus restoring the integrity of the corneoscleral coat over the excision (Fig. 1a-e). These procedures enabled tight suturing of the conjunctival flap and scleral flap (Fig. 1h-i), absence of filtering blebs (Fig. 3), and well controlled IOP (Fig. 2).

Trabeculo-canalectomy, which is bleb-independent, significantly reduces the incidence of filtering bleb- and antimetabolite-related complications, which are frequent in trabeculectomy [10, 26,27,28]. Additionally, post-operative interventions of filtering blebs [29], such as releasable sutures and bleb needling, were not necessarily performed in our research. Third, tight suturing of the conjunctival flap and scleral flap significantly reduces complications early after surgery [30], such as hypotony and shallow anterior chamber related to over-filtration. Hypotony occurs in 10–37.5% cases after traditional Trab [9, 31], but none after trabeculo-canalectomy in the present study. In summary, trabeculo-canalectomy facilitates aqueous outflow and restores filtration through Schlemm’s canal, demonstrating long-term efficacy and safety for PACG patients.

Designed according to a concept of “internal drainage” (similar to ours), penetrating Schlemm canaloplasty has been first composed by Professor Liang in 2015, and also achieved remarkable clinical success [9, 32,33,34,35]. In this surgery, a direct communication is established between the anterior chamber and the Schlemm’s canal to restore aqueous humor outflow in PACG patients, thus combining the advantages of suture tensioning canaloplasty with Trab. The success rate of this surgery can reach 86.8% in PACG patients [9, 34]. However, in Liang’s surgery, Schlemm’s canal needs to be perforated by microcatheter throughout the operation, and tensioning suture serves to keep Schlemm’s canal patent [9, 35]. As a consequence, this surgery procedure is relatively complex for clinicians, and their long learning curve may also lead to clinical failure in some cases. Additionally, the microcatheter used during the procedure is expensive [36].

In comparison, our trabeculo-canalectomy is relatively simple and cost-saving, mainly including the following steps: a superficial scleral flap, 4 × 4 mm and 1/2 scleral thickness, was forwarded into the clear corneal limbus by about 1 mm. Then, the clear corneal area and the white sclera area were identified. The gray zone, also known as the grayish blue trabecular meshwork, was delineated. The Schlemm’s canal runs at the junction between the grayish blue trabecular meshwork and the white sclera, and the Schlemm tube was accurately located at the posterior 1/2 of the gray area (Fig. 1b). At this time, the outer wall of the Schlemm’s canal was gently lifted by microscope forceps, and then opened to expose its cavity more easily (Fig. 1b-c). Before opening the Schlemm’s canal, anterior chamber paracentesis was performed to prevent the iris from excessively prolapsing to the incision site. Since the Schlemm’s canal is close to the root of the iris, it is recommended to clip the iris slightly away from the Schlemm’s canal and perform iridectomy to reduce iris bleeding (Fig. 1f). The scleral and conjunctival flaps were tightly sutured with 10 − 0 nylon suture to avoid early filtration (Fig. 1h-i).

Notably, though simple and cost-saving trabeculo-canalectomy provides favorable 5-year outcomes in the treatment of PACG, the procedure may not achieve similar efficacy in patients with certain types of glaucoma, the pathophysiology of which may lie beyond the Schlemm’s canal, such as primary open-angle glaucoma (POAG). The developmental abnormalities in the outflow routes and collapse of Schlemm lumen have been reported in POAG patients [37]. The cutting ends of Schlemm’s canal may be more prone to the occurrence of adhesion and closure in POAG patients. In addition, our previous research shows that patients with secondary glaucoma, especially uveitic glaucoma, were more likely to undergo surgical failure [16]. Adequate anti-inflammatory therapy combined with antimetabolic drugs is often needed in the surgical treatment of uveitic glaucoma.

There are some limitations in this study. First of all, only PACG patients in China were included, and our surgery may not be suitable to PACG patients in other countries. Part of the patients included were binocular, and the statistical results may have been biased. Second, the sample size of this study was small. In addition, aqueous oozing from the Decemet’s membrane and trabecular meshwork is a marker for the positioning of the canal of Schlemm. However, due to the extensive peripheral anterior synechiae and obstruction of the trabecular meshwork, aqueous oozing is infrequent in PACG eyes, thus challenging the recognition of the Schlemm’s canal in PACG patients. This requires a learning curve for a surgeon. More randomized controlled trials should be conducted in the near future to directly compare the efficacy, safety and cost-effectiveness of this procedure with Trab.

Conclusion

Tabeculo-canalectomy provides favorable 5-year outcomes in treating medically uncontrolled PACG, as shown by effective IOP control, obvious drug reduction, as well as less post-operative interventions compared to Trab.

Data availability

The datasets used and/or analysed during the current study are available from the corresponding author on reasonable request.

Abbreviations

PACG:

Primary angle-closure glaucoma

POAG:

Primary angle-open glaucoma

IOP:

Intraocular pressure

Trab:

Trabeculectomy

IBAGS:

Indiana Bleb Appearance Grading Scale

BCVA:

Best-corrected visual acuity

LPI:

Laser peripheral iridotomy

SD:

Standard deviation

Meds:

Medications

SUM:

Summary

N:

Number

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Acknowledgements

We would like to thank Yong-ke Cao for proofreading of the manuscript.

Funding

This study was supported by a grant from the National Natural Science Foundation of China (Grant Number: 82401281).

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Author notes

  1. Zhan Xie and Tianhao Xiao contributed equally to this work.

Authors and Affiliations

  1. Department of Ophthalmology, the First Affiliated Hospital of Nanjing Medical University, 300 Guangzhou Road, Nanjing, 210029, Jiangsu Province, P.R. China

    Zhan Xie, Tianhao Xiao, Junlong Huang, Ping Zhang, Ping Xie & Hong Sun

  2. Department of Biostatistics, School of Public Health, Nanjing Medical University, Nanjing, 210029, Jiangsu Province, China

    Mulong Du

  3. R&D Department, BioTissue, Miami, FL, 33126, USA

    Ying-Ting Zhu

Authors
  1. Zhan Xie
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  2. Tianhao Xiao
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Contributions

ZX, THX, PX and HS designed the research project; ZX, THX, JLH, and PZ performed the research; ZX and MLD analyzed the data; ZX wrote the manuscript draft; MLD, YTZ, PX and HS revised the manuscript.

Corresponding authors

Correspondence to Ping Xie or Hong Sun.

Ethics declarations

Ethics approval and consent to participate

This was a retrospective study approved by the First Affiliated Hospital of Nanjing Medical University (No.2023-SR-474), abiding by the Declaration of Helsinki. Written consent was obtained from all patients before surgery.

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Not applicable.

Competing interests

The authors declare no competing interests.

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Xie, Z., Xiao, T., Huang, J. et al. Five-year outcomes of trabeculo-canalectomy for Chinese PACG patients: a retrospective study. BMC Ophthalmol 25, 234 (2025). https://doiorg.publicaciones.saludcastillayleon.es/10.1186/s12886-025-04051-6

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  • DOI: https://doiorg.publicaciones.saludcastillayleon.es/10.1186/s12886-025-04051-6

Keywords

BMC Ophthalmology

ISSN: 1471-2415

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