We conducted a retrospective analysis of the first 11 consecutive eyes from nine patients who underwent GATT at Kibagabaga Hospital between 01 January 2023 and 28 August 2023. Patients were identified using manual review of electronic and paper surgical records (using the key terms ‘GATT’ and ‘gonioscopy assisted transluminal trabeculotomy’). Glaucoma was diagnosed in patients with characteristic optic nerve head changes, visual field defects and thinning of the retinal nerve fibre layer as measured by optical coherence tomography. Gonioscopy was performed on all patients. Exclusion criteria for consideration of GATT as a treatment option included active neovascular glaucoma and lack of an adequate view of the angle on gonioscopy (including due to cicatricial angle closure) to perform GATT safely. A total of 260 eye surgeries were performed at Kibagabaga during this period, of which 11 were GATT procedures. The full surgical technique is described in Online Appendix 1. A summary of the technique is as follows: Using a surgical, direct-viewing gonioscopy lens, a 23G needle was passed into the anterior chamber and used to perform a 2 mm – 3 mm nasal goniotomy. 5-0 Prolene suture (needle removed and blunted) was threaded into the goniotomy incision using 23G intraocular forceps. The proximal flanged end of the suture was retrieved at the goniotomy incision. While holding the flanged end intraocularly, the extraocular, distal end of the suture was grasped with a needle driver and pulled, tearing the intraocular suture through the trabecular meshwork. This created a 360-degree, ab interno goniotomy.

All patients were recommended to follow-up at a minimum on post-operative day 1 (POD1), post-operative week 1 (POW1), post-operative month 1 (POM1) and post-operative month 3 (POM3). These intervals were modelled with few modifications after the original Grover et al. paper describing this surgical technique, unless specific post-operative concerns merited closer follow-up.^3,7 All available data were collected and reported from visits through 01 February 2024. All patients had at least one visit more than 3 months post-operatively that included a full exam, apart from one patient who was lost to follow-up (LTFU).

Our primary outcome was IOP reduction from medically treated, baseline pre-operative IOP on the last exam before surgery. An outcome of complete success was defined as a post-operative IOP between 5 mmHg and 21 mmHg while demonstrating at least a 20% reduction from pre-operative baseline IOP (after POM1) without glaucoma medication or further glaucoma procedures (Table 1). A qualified success was defined as an IOP between 5 mmHg and 21 mmHg with a 20% lowering from baseline IOP with glaucoma medication after POM1. Failure was defined as IOP ≥ 21 mmHg and < 5 mmHg at the last visit, worsening of vision from baseline at the last visit or the need for additional glaucoma surgery^7,9(Table 1). Other outcomes of interest included the number of glaucoma medications needed post-GATT, the number of surgeries post-GATT and visual acuity. Intraocular pressure was measured either using an iCare tonometer (Vantaa, Finland) or with Goldmann applanation (Haag-Streit Diagnostics, Switzerland) by ophthalmology residents at Kibagabaga.

Study data were collected and managed using REDCap electronic data capture tools hosted at the Perelman School of Medicine.^10,11 Research Electronic Data Capture (REDCap; Vanderbilt University, Nashville, TN, United States) is a secure, web-based software platform designed to support data capture for research studies, providing: (1) an intuitive interface for validated data capture; (2) audit trails for tracking data manipulation and export procedures; (3) automated export procedures for seamless data downloads to common statistical packages; and (4) procedures for data integration and interoperability with external sources.

The data collected were entered, analysed and processed using Stata BE statistical software, version 18.0 (StataCorp, College Station, TX, United States). The p-value and 95% confidence interval were calculated, and a Chi-square test with Fisher’s exact test was used to compare success across surgical categories, given the small sample size. Results were statistically significant when the p-value was < 0.05.

Our case series included 11 operative eyes in 9 patients, two of whom underwent bilateral surgery, with chronic angle closure glaucoma (CACG) and primary open angle glaucoma (POAG) as the most common glaucoma diagnoses Table 2 and Table 3). This patient population had severe glaucoma; the only patients who underwent GATT with mild-to-moderate glaucoma were paediatric patients with either congenital or steroid-induced glaucoma (3, 27%). In these younger patients, the higher predicted years lived with disability if left untreated motivated the utilisation of GATT as an earlier surgical option versus trabeculectomy. The mean baseline treated IOP was 25 mmHg, with a standard deviation of 7.7 mmHg. A majority of eyes (7, 64%) had pre-operative best-corrected visual acuity worse than 6/12. We report pre-operative IOP on optimised medical treatment; while on treatment, 8 (73%) eyes still had IOPs greater than 21 (Table 3).

The change in IOP after treatment is shown in Figure 1 and Table 4. The mean IOP at POM3 was 13 mmHg (s.d. 4.7). Success was observed across all surgical types: standalone GATT, GATT and manual small incision cataract surgery (MSICS), and GATT with phacoemulsification cataract surgery (phaco) (Table 4; Figure 2). All patients who underwent GATT with phaco achieved success. At POM3, all patients achieved at least a 20% reduction in IOP, as shown in Figure 3. One case that had undergone a standalone GATT met failure criteria due to a spike in pressure to 25 mmHg on their POM6 visit after consistent pressures lower than 21 mmHg. One patient who had also undergone a standalone GATT was LTFU after POW4, but at this visit, they had met criteria for a qualified success.

Fifty five percent of patients did not require any glaucoma drops after surgery. Four patients required glaucoma drops in the first 90 days post-operatively, one of whom only required drops within the first 3 post-operative days. This also includes a patient who was LTFU, presumably continued IOP-lowering drops more than 90 days after surgery. No patients had any other glaucoma surgeries in the follow-up period. A best corrected visual acuity of greater than 6/12 was seen in 9 eyes (82%) post-operatively, meeting the WHO-recommended threshold for a ‘good quality visual outcome’.¹² Visual improvement was likely because of cataract surgery rather than GATT itself; importantly, no patients had a decline in visual acuity after receiving GATT surgery. Complications stratified by surgical type are detailed in Table 5.

This retrospective case series demonstrates that GATT is a useful tool in the arsenal of pressure-reducing treatments for the patients of the Kibagabaga District Hospital and the Rwanda International Institute of Ophthalmology. A majority of patients, many of whom had severe glaucoma, achieved successful pressure reduction and experienced few complications. We also re-demonstrate that lensectomy, where appropriate, concurrent with the GATT procedure, often yields a positive pressure-reducing effect.^12,13

One case met criteria for failure; however, its unique context merits further discussion. This patient was a teenager post-traumatic cataract extraction with intraocular lens implant with a history of persistent pseudophakic cystoid macular oedema treated medically with injections of anti-vascular endothelial growth factor and eventually sub-Tenon’s triamcinolone. He then developed steroid response glaucoma with pressures in the 40s mmHg whenever oral acetazolamide was tapered off. This necessitated surgical intervention. Post-operatively, he had a pressure spike to 25 mmHg at POM6. Although this pressure measurement exceeded our desired cutoff, the therapeutic reduction of 20 mmHg is significant (> 30%) and may be sufficient to prevent further damage to the optic nerve at his age. However, according to our predetermined criteria, this clinically significant outcome still must be listed as a failure. They were restarted on glaucoma medications in the operative eye at their last visit.

Although we cannot predict outcomes for success or failure given our small sample size, some observations can be made. A Fisher’s exact test showed no statistically significant difference between the degree of IOP reduction with GATT when stratified by type of glaucoma or by GATT alone versus GATT with lensectomy. Another similar study reports greater rates of successful GATT surgery in POAG patients.¹⁴ All patients with narrowing of the angles at play (CACG and mixed mechanism) achieved medication-sparing pressure reduction success. All patients, except one who received lensectomy (phaco or MSICS) in addition to GATT, met success or qualified success criteria, possibly highlighting the known pressure-reducing effect of lensectomy.^12,13

Intraocular pressure spikes are a known complication of GATT surgery.^15,16,17 In our case series, this complication was not seen in patients who also underwent lensectomy. The pressure spikes seen in two patients resolved within POW1 after short-term pressure-reducing treatment, and all patients with spikes achieved complete success. Hyphema, another previously documented complication of GATT, was also seen in two patients who achieved qualified success.^15,17 Descemet detachment was seen in a patient who underwent GATT; thus, the endothelial detachment could have been because of the cataract surgery itself.¹⁸ The detachment was small and did not require further surgical intervention.

In a few patients, peripheral anterior synechiae (PAS) were noted in the angle at POM6 and later visits. This has been observed in other studies but has not been demonstrated to affect IOP outcomes.^15,16 Surgical traumas to the trabecular meshwork likely promote fibrin deposition and scar formation, explaining this finding. We saw more PAS in our younger patients and hypothesise that their age may contribute to a more robust fibrotic reaction. Prevention and control of hyphema and inflammation have been postulated as ways to reduce the risk of PAS formation.¹⁶ Using topical pilocarpine 1% twice daily beginning 1 week postoperatively could also be considered, with its miotic action serving to retract the peripheral iris, thereby preventing angle scarring.

There are limitations to this case series. Our sample size is small, limiting statistical power, the ability to perform multivariate or subgroup analysis and generalisability. Additionally, this is a retrospective study with limited follow up. A prospective, larger, long-term study would be helpful to improve validity and further assess outcomes of this procedure. Our baseline IOP was measured on treatment with no untreated values or washout period, largely because not all patients had recorded untreated pre-operative IOP. This can also be remedied with a prospective study. Given our baseline was treated pre-op IOP, we also highlight that there is likely an even greater degree of pressure-lowering potential after GATT than captured in our data. There was difficulty with patient adherence to preferred follow-up timelines. Despite this, we were able to get valuable post-operative evaluations for most patients. Qualitative data collected from patients demonstrated that transportation and travel distance were clear barriers to follow-up and scheduled IOP checks. This highlights a known social determinant of health, neighbourhood and built environment, that has been documented to affect access and utilisation of eye care.¹⁹ This also emphasises the great need to not only increase the number of highly skilled ophthalmologists in Rwanda but also their spread to rural areas in order to decrease the travel burden placed on patients who seek care. The various forms of medical records (paper and electronic concurrently) also created some inconsistencies and gaps in records. It is possible that some visits were not captured in these records and have not been included in our data set. Additionally, visual field data were not consistently available for all patients and, therefore, could not be included in the analysis. In the future, the clinic is working to streamline its medical record system to avoid these kinds of challenges. A single surgeon performed the surgeries, providing an internal control. Intraocular pressure was measured by other physicians to avoid bias.

This case series demonstrates that GATT is an accessible MIGS option for patients with various forms of glaucoma in lower-resource settings.²⁰ Our patient cohort saw a mean IOP decrease of 13 mmHg at POM3 compared to their pre-op treated IOP. As efforts continue to increase equitable access to MIGS options around the world, we highlight GATT as a validated procedural option and encourage training in this procedure.