Optimizing the sequential approach of combined phacoemulsification and gonioscopy-assisted transluminal trabeculotomy (GATT) in primary open-angle glaucoma

Abstract

Background

To evaluate the efficacy, safety and complication of different procedure sequence combining gonioscopy-assisted transluminal trabeculotomy (GATT) either before or after phacoemulsification for patient with primary open-angle glaucoma (POAG) and cataract.

Method

This retrospective, clinic control study included 82 patients (82 eyes) with a diagnosis of POAG with cataract. The patients were divided into two groups: Phaco-GATT group underwent phacoemulsification followed by GATT and GATT-Phaco group underwent GATT followed by phacoemulsification. Intraocular pressure (IOP) changes, best-corrected visual acuity (BCVA), visual field Mean Deviation (MD) and antiglaucoma medication (AGM) were analyzed preoperatively and at postoperatively 1d, 1w, 1 m, 3 m, 6 m, and 12 m. Postoperative complications, including hyphema, IOP spikes, and suprachoroidal effusion, were closely reported.

Result

A total of 40 eyes were subjected to Phaco-GATT group, and 42 eyes were subjected to GATT-Phaco group. For all patients, significant IOP and AGM reduction and BCVA improvement were observed at each follow-up time points compare to preoperation (all P > 0.05). At 12 months, the visual field MD in the GATT-Phaco group was significantly improved than that in the Phaco-GATT group (P < 0.05). GATT-Phaco group appeared to have less AGM than those in Phaco-GATT group from postoperative 1 month to 12 months, though there was no significantly difference (all P > 0.05). At 12 months postoperatively, GATT-Phaco group demonstrated a slightly higher complete success rate of 76.2% and qualified success rates of 90.5% compare to Phaco-GATT (65.0% and 85.0%). Moreover, in the GATT-Phaco group, BCVA was significantly improved and macrohyphema (> 1 mm) was reduced compare to Phaco-GATT group at early stage. Additionally, no statistically significant differences were observed in IOP spike, descemet’s membrane detachment, and supraciliary effusion between two groups at each time point.

Conclusion

This study demonstrates that combined phacoemulsification and GATT is a safe and effective treatment for POAG patients with cataract. Both surgical sequences are effective, however, initiating with GATT may provide more benefits compare phacoemulsification prior.

Background

Primary open-angle glaucoma (POAG) poses a significant global health challenge, affecting millions worldwide and leading to irreversible vision loss [1]. And it characterized by a progressive optic neuropathy, often associated with elevated intraocular pressure (IOP) [2, 3]. Given the irreversible nature of glaucomatous damage, timely and sustained IOP control is critical in managing POAG and preventing vision loss [4]. Trabeculectomy used to be considered gold standard surgical for POAG to create an alternative pathway for aqueous humor outflow, effectively lowering IOP. However, trabeculectomy is associated with potential complications, such as bleb-related infections, choroidal effusion, hypotony, and scarring, which can compromise its long-term success. Additionally, postoperative management requires close monitoring, and the outcome can be highly variable depending on patient-specific factors [5].

In recent years, minimally invasive glaucoma surgery (MIGS) emerging as a promising alternative. Gonioscopy-assisted transluminal trabeculotomy (GATT) is one of MIGS procedure, first described by Grover et al. in 2014, represents a novel approach for treat POAG [6]. GATT is effective in both short-term and long-term stages to control IOP without too much complications compare to traditional trabeculectomy [7]. GATT involves a 360° trabeculotomy, which restores natural aqueous outflow through Schlemm’s canal without creating an external filtering bleb, thereby reducing the risks of bleb-related complications. Its minimally invasive nature typically results in faster recovery times and a lower risk profile, making it an attractive option especially when conjuncted with cataract surgery [8, 9]. For patients with POAG and cataract, the combination of GATT and cataract surgery has presented as a highly effective treatment strategy to provides significant IOP reduction and improves visual acuity.

In general, performing cataract surgery first may provide the benefit of better exposing the iris root area, thereby creating more anterior chamber spaces and better vision for the subsequent GATT procedure. However, the changes of the anterior chamber and also angle structure destruction after phacoemulsification may complicate the GATT procedure, leading to the postoperative eye more prone to inflammation and higher IOP. This study will compare the outcomes between performing phacoemulsification first versus GATT first to assess complications and efficacy to determine the the optimal sequence for enhancing safety, surgical efficiency, and patient outcomes in the combined management of POAG and cataracts.

Methods

Patients

We undertook a retrospective clinic control study which recruited consecutive patients diagnosed with POAG and cataract in 82 patients during 2023.01 to 2023.09 at the Department of Ophthalmology, the People’s Hospital of Guangxi Zhuang Autonomous Region, China. Patients were categorized into two groups based on the surgical sequence: Phaco-GATT (n = 40) underwent phacoemulsification followed by suture-guided GATT, while GATT-Phaco (n = 42) underwent suture-guided GATT followed by phacoemulsification. All had 12 months of observation followed up were included. This study was approved by the People’s Hospital of Guangxi Zhuang Autonomous Region Ethics Committee, adhered to the tenets of the Declaration of Helsinki.

The inclusion criteria were patients with POAG and cataract (1) aged between 50 and 75 years; (2) preoperative IOP ≥ 21 mmHg on maximal medications; (3) glaucomatous visual field defects; (4)open-angle configuration on gonioscopy with typical glaucomatous optic neuropathy (neural rim thinning, focal notching, vertical cup-to-disc ratio > 0.6, or cup-to-disc ratio asymmetry ≥ 0.2); (5)trabecular meshwork pigmentation grade< II. (6)cataract with lens nuclear grade ≤ IV (LOCS III classification) and best-corrected visual acuity (BCVA) ≤ 0.5 logMAR. Patients with other types of glaucoma, a history of ocular trauma, a history of ocular, corneal abnormality that can’t measure the angle configuration or IOP, corneal endothelial cell density of ≤ 800 cells/mm², unable to comply with postoperative follow-up, and patients who were on anticoagulant therapy were excluded.

Surgical procedure and postoperative care

Surgery was performed as a stand-alone procedure by one surgeon (ZSY). We follow the standard preoperative dilation protocol for phacoemulsification, with no additional miotic or mydriatic agents needed during surgery. A clear corneal incision of 2.2 mm was performed at 10:00 after peribulbar anesthesia. Then, a corneal paracentesis track, oriented tangentially, was then placed at 2:00, and viscoelastic (sodium hyaluronate) was injected into the anterior chamber. For Phaco-GATT, a standard phacoemulsification procedure was performed first, and an IOL was placed in the posterior chamber of the bag. Following phacoemulsification, patients underwent a suture-guide GATT procedure. A auxiliary incision was created at 7:00, viscoelastic was injected to deepen the anterior chamber, and a polypropylene suture was passed into the anterior chamber. Under surgical microscope and gonioscopic guidance, a 2 mm incision was made using a 1 mL syringe in the nasal or inferior trabecular meshwork and the inner wall of Schlemm’s canal. A 5 − 0 polypropylene suture was inserted into Schlemm’s canal through the trabecular incision with 23-gauge forceps, advancing it circumferentially around the canal. The suture was then retrieved from the opposite end of Schlemm’s canal, both ends were grasped within the anterior chamber, and traction applied to create a 360° circumferential opening of the trabecular meshwork, exposing the Schlemm’s canal lumen. All GATT procedures in the Phaco-GATT group were successfully completed following phacoemulsification. In GATT-Phaco, GATT was performed first (as detailed for Phaco-GATT), followed by phacoemulsification. Following surgery, viscoelastic and hyphema were removed using an irrigation/aspiration (I/A) handpiece. In the end, the anterior chamber was irrigated and reformed with balanced salt solution (BSS), and the corneal incisions were hydrated with to ensure watertight closure. Postoperatively, tobramycin-dexamethasone ointment was applied, and the eye was patched. Tobramycin-dexamethasone eye drops four times daily for two weeks and 0.5% pilocarpine nitrate eye drops four times daily for four weeks.

Clinical characteristic evaluation

Follow-ups were completed at postoperative 1 day, 7 days, 1 month, 3 months, 6 months, and 12 months. At each time point, the following data were recorded: IOP, BCVA and antiglaucoma medications (AGM), surgical success rate, surgery-related complications (including IOP spikes, hyphema, cyclodialysis cleft, and choroidal detachment). Visual field tests were performed preoperatively and at 6 and 12 months postoperatively to record the visual field Mean Deviation (MD). Surgical success was categorized as follows: (1) Complete success: postoperative IOP ≤ 18mmHg and ≥ 20% reduction from baseline without AGM; (2) Qualified success: postoperative IOP ≤ 18mmHg with 1–2 AGM; (3) Failure: IOP > 18mmHg requiring ≥ 2 medications, or requiring additional glaucoma surgery due to uncontrolled IOP. Postoperative IOP spike: IOP ≥ 30 mmHg within postoperative one month. Microhyphema was defined as blood visible in the anterior chamber or blood occupies ≤ 1 mm; while Macrohyphema was defined as blood occupies > 1 mm [10].

Statistical analysis

SPSS software, Version 22.0 (IBM Corp, Armonk NY), were used to analyse data and generate figures. Normally distributed continuous data (Repeated measures ANOVA) were presented as means ± standard deviations (Mean ± SD). When significant differences were detected, post-hoc analyses were conducted using the Least Significant Difference (LSD) t-test for within-group comparisons and independent samples t-test for between-group comparisons. Categorical data were expressed as frequencies and percentages, Chi-squared test and Fisher’s exact test were used for comparison of proportions between the two groups. Kaplan-Meier survival analysis was utilized to evaluate success rates. Statistical significance was set at p < 0.05.

Results

Demographics and baseline ocular characteristics

Patient demographic and baseline ocular characteristics are summarized in Table 1. In total, 82 patients (40 patients in Phaco-GATT and 42 patients in GATT-Phaco) met the inclusion criteria and comprised the study population. The average age was 64.88 ± 5.99 years, 48 (58.5%) patients were male and 34(41.5%) were female. No significant differences of age, sex, BCVA, IOP and AGM were present between Phaco-GATT and GATT-Phaco groups (p > 0.05, for all).

Table 1 Demographics and baseline ocular characteristics

Surgical outcome

Overall, as shown in Fig. 1; Table 2, the mean IOP and number of AGM were significantly decreased at all postoperative visits compared to baseline (all P < 0.001). The average IOP and AGM were reduced from 30.80 ± 4.14 mmHg and 2.76 ± 0.62 at baseline to 13.33 ± 3.20mmHg and 0.11 ± 0.31 at postoperative 1 day, 14.83 ± 1.97mmHg and 0.39 ± 0.78 at postoperative 6 months, 14.77 ± 2.13mmHg and 0.48 ± 0.86 at postoperative 12 months, respectively (all P > 0.05). From postoperative 1 day to 12 months, the IOP and AGM were slightly increased. In both subgroups, the mean IOP and antiglaucoma medication were significantly decreased at every follow-up time point compared to baseline. Although the two groups did not differ significantly in terms of mean IOP or number of AGM at any follow-up visit (all P > 0.05), GATT-Phaco appeared to have less AGM than those in Phaco-GATT at 1 month (0.15 ± 0.36 vs. 0.07 ± 0.26, P = 0.557), 3months (0.40 ± 0.74 vs. 0.21 ± 0.52, P = 0.261), 6 months (0.50 ± 0.85 vs. 0.29 ± 0.71, P = 0.192), 12 months (0.48 ± 0.86 vs. 0.55 ± 0.88, P = 0.40 ± 0.86).

Fig. 1

Comparison of IOP between different groups at different time points before and after surgery. IOP= intraocular pressure; Phaco=phacoemulsification; GATT= gonioscopy‑assisted transluminal trabeculotomy

Table 2 Comparison of AGM use between two groups at different time points before and after surgery

At 12 months postoperatively, the overall complete and qualified surgical success rates were 70.7% and 87.8%, respectively. Phaco-GATT achieved a complete success rate of 65.0% and qualified success rates of 85.0%, whereas GATT-Phaco showed a slightly higher rate of 76.2% and qualified success rates of 90.5%. However, this difference of complete success rates (χ2 = 1.446, P = 0.226) and qualified success rates (χ² = 0.609, P = 0.435) did not reach statistical significance. The Kaplan-Meier survival curves for both groups are presented in Fig. 2.

Fig. 2

Kaplan–Meier analysis of the cumulative probabilities of surgical success. Phaco=phacoemulsification; GATT= gonioscopy‑assisted transluminal trabeculotomy

Visual acuity and visual field

As shown in Table 3, postoperative BCVA significantly improved from baseline across all time points, both overall and within the Phaco-GATT and GATT-Phaco subgroups (all P < 0.001). Interestingly, we observed a transient decline in mean BCVA on the first postoperative day across all groups. However, by 1 week postoperatively, significant improvement was noted, and visual acuity stabilized after 1 month. Mean BCVA improved markedly from 0.75 ± 0.36 logMAR to 0.26 ± 0.16 logMAR overall, 0.78 ± 0.40 logMAR to 0.28 ± 0.19 logMAR in Phaco-GATT, 0.71 ± 0.33 logMAR to 0.24 ± 0.12 logMAR in GATT-Phaco at 3 months postoperatively (P < 0.001). In addition, subgroup analysis revealed significantly differences between Phaco-GATT and GATT-Phaco at early stage postoperatively. Notably, in the GATT-Phaco group demonstrated superior BCVA compared to Phaco-GATT group at both 1 day and 1 week postoperatively (P < 0.05).

Table 3 Comparison of best corrected visual acuity between two groups at different time points before and after surgery

Table 4 shows that 65 patients underwent visual field testing preoperatively and at 6 and 12 months postoperatively. The results demonstrated no significant changes in MD in the GATT-Phaco group when comparing preoperative values with those at 6 and 12 months postoperatively (P > 0.05). However, in the total patient group and the Phaco-GATT group, MD at 6 and 12 months showed a trend toward progression compared to baseline (P < 0.05). Furthermore, at 12 months, the MD in the GATT-Phaco group was significantly better than that in the Phaco-GATT group (P < 0.05).

Table 4 Comparison of visual field mean deviation (MD) between two groups at different time points before and after surgery

Complications

Table 5 summarizes the postoperative complications observed in both groups, including hyphema, IOP spikes, descemet membrane detachment, and supraciliary effusion. There’s no any cataract surgeries complications like posterior capsule rupture, intraocular lens (IOL) dislocation, or other cataract surgery-related complications happened. The incidence of IOP spikes no statistically significant difference (χ2 = 0.032, p = 0.857)., with Phaco-GATT experiencing a rate of 17.5% and GATT-Phaco 19.0%. Similarly, the rates of supraciliary effusion were 27.5% in Phaco-GATT and 32.5% in GATT-Phaco, again without a statistically significant difference (χ2 = 0.256, p = 0.613). However, Phaco-GATT exhibited a significantly higher incidence of Macrohyphema(42.5%) compared to GATT-Phaco (23.8%, p < 0.001). The majority of these hemorrhages resolved spontaneously within two weeks postoperatively.

Table 5 Surgical and postsurgical ocular-related complications

Discussion

GATT has emerged as a safe and effective MIGS technique, offering a promising alternative to traditional filtering surgeries by utilizing a gonioscope to perform a 360-degree incision of the Schlemm’s canal [6]. A key advantage of GATT is its ability to effectively restore physiological aqueous humor circulation and lowers IOP without creating a filtration bleb, thereby minimizing the risk of bleb-related complications. The safety and efficacy of GATT have been well documented in recent clinical studies, with success rates ranging from 60 to 90% in different populations, which are consist with our results [11]. Notably, GATT has primarily been applied in the management of POAG, including both primary and secondary forms, and has also shown potential in treating angle-closure glaucoma [12, 13].

For patients with POAG and cataract, the procedure is primarily performed GATT combined with cataract phacoemulsification. In a 6 months follow-up study, Baykara et al. demonstrated the efficacy of combined GATT and phacoemulsification in patients with POAG and coexisting cataracts. At 6 months postoperatively, the mean visual acuity improved from 1.57 ± 1.2logMAR preoperatively to 0.39 ± 0.38logMAR, IOP decreased from 34.2 ± 10.6 mmHg to 11.2 ± 2.4mmHg. Additionally, the number of AGM required was reduced by an average of 2.7 ± 0.6 [14]. Another 2 years follow-up study showed that the combined procedure significantly reduced IOP from a preoperative mean of 26.40 ± 6.37 mmHg (3.12 ± 0.80 AGM) to 16.08 ± 2.38 mmHg at postoperative 24 months (0.45 ± 0.96 AGM). Furthermore, BCVA improved substantially, from 0.75 ± 0.43 logMAR to 0.22 ± 0.18 logMAR [15]. Our findings are consistent with previous studies, demonstrating that the combination of phacoemulsification and GATT significantly reduces IOP and improving visual acuity in patients with POAG and cataract. The most important, compare to Phaco-GATT group, the MD in the GATT-Phaco group was significantly better and slightly slower reduce. These results suggest that GATT, as a standalone or combined procedure, can be an effective treatment strategy for glaucoma patients, offering a viable solution with favorable outcomes.

In clinic, phacoemulsification is usually performed first in GATT combined surgeries. This sequence allows for a clearer view of the anterior chamber and better access to the trabecular meshwork by removing the cataract lens beforehand. However, Fellman et al. described an important clinical indicator of functional aqueous outflow through Schlemm’s canal and collector channels into the episcleral venous system, termed the episcleral venous fluid wave (EVFW) [16,17,18]. In this study, we performed GATT prior to phacoemulsification, EVFW may be among the possible factors influencing outcomes. Unfortunately, in this research, we didn’t have some indicators to assess EVFW. Just the surgeon observed aqueous humor successfully enters the episcleral venous system after GATT did. We hypothesize that performing GATT first establishes an outflow pathway earlier in the procedure, potentially allowing for a more robust and immediate aqueous flow through the newly created drainage channels. This stronger wave may serve as a positive response to trabeculotomy, helping to lower IOP during surgery, protect the retina, and ultimately optimize overall outcomes. These hypothesis is consist with our results, the MD of Phaco-GATT group at 6 and 12 months showed a trend toward progression compared to baseline and also GATT-Phaco group. Despite there were no significantly difference of IOP, antiglaucoma medication, visual acuity, and success rates between Phaco-GATT and GATT-Phaco groups. Overall, the surgical sequence may influence the retinal damage and result in a visual field reduction.

Previous studies have consistently demonstrated that GATT is associated with a low incidence of vision-threatening complications. While the most frequently reported complications included hyphema, IOP-Spike, descemet membrane detachment, supraciliary effusion, and peripheral anterior synechiae [19, 20]. These events were mostly self-limiting and did not significantly impact long-term visual outcomes. Sato et, al. detected that the presence of hyphema by the GATT implant results from retrograde flow of blood into the anterior chamber due to the pressure gradient between the episcleral veins and the lowered IOP following successful drainage [21]. So their research suggests that hyphema may serve as an indicator of surgical success. Interestingly, Devendra et, al. showed that the incidence of postoperative hyphema is significantly lower in combined GATT and phacoemulsification procedures compared to GATT alone [22]. This phenomenon is attributed to the aspiration of refluxed blood during cataract surgery, as well as the elevated IOP during the procedure, which may prevent episcleral venous blood from flowing back into the anterior chamber. Our results indicated that a lower incidence of post-operative macrohyphema in GATT-Phaco compared to Phaco-GATT. This difference may be attributed to the extended duration of elevated IOP when GATT is performed before phacoemulsification in GATT-Phaco. The sustained high pressure, along with continuous perfusion and aspiration, effectively removes refluxed blood and reduces blood flow back into the anterior chamber. These combined factors appear to contribute to a reduced volume of hyphema. Furthermore, GATT-Phaco demonstrated a significant advantage visual acuity one week postoperatively compared to Phaco-GATT. This improved visual recovery may be directly linked to the lower incidence of post-operative macrohyphema in GATT-Phaco, which facilitates a faster postoperative recovery. Hence, these findings suggest that performing GATT prior to cataract surgery in combined procedures potentially optimizes both the safety profile and short-term outcomes.

Suprachoroidal effusion is a complication that arises due to traction on the ciliary muscle fibers during the formation of a trabeculotomy incision in GATT, potentially leading to ciliary body detachment and IOP reduction. Previous studies have reported incidence rates of 47.7% and 42% for suprachoroidal effusion following GATT [21, 23]. In our study, the incidence of suprachoroidal effusion was 27.5% in Phaco-GATT and 32.5% in GATT-Phaco, consistent with these reports. Another common complication following GATT is an IOP spike, with studies reporting an incidence rate between 8.2 and 24% [24,25,26]. While IOP spikes may be related to hyphema and postoperative steroid use. Shi et al. observed that eyes undergoing ciliary body detachment and resolving suprachoroidal effusion were more prone to IOP spikes, suggesting a potential relationship [27]. However, they suggested that suprachoroidal effusion might merely delay the onset of IOP spikes rather than cause it. In this study, the incidence of IOP spikes was 17.5% in Phaco-GATT and 19.0% in GATT-Phaco, with no significant difference between the groups. Despite the slightly higher incidence of suprachoroidal effusion in GATT-Phaco, these findings could suggest a potential connection between the absorption of suprachoroidal effusion and the occurrence of IOP spikes.

Our study has some limitations, such as a relatively small sample size, a limited follow-up duration, and unclear mechanisms of complications. Its nonrandomized design may have also contributed to selection bias, as the decision to perform GATT could have been influenced by the surgeon’s preference over other surgical techniques. Despite these limitations, our research contributes to demonstrating the efficacy and safety of GATT combined with phacoemulsification in patients with POAG and cataracts. To better understand this surgical approach and evaluate its advantages, there is a need for optimized clinical trial designs and larger sample sizes in future research.

Conclusions

In conclusion, the combination of GATT with cataract phacoemulsification effectively reduces IOP, protect visual field and decreases the reliance on AGM. Compared to performing phacoemulsification followed by GATT, initiating with GATT prior may result in less significant macrohyphema and potentially better early postoperative visual outcomes, slightly better visual field, and be a better surgical sequence approach in managing POAG with cataracts.