Relationship between Schlemm's canal incision length and the results of ab interno gonioscopy-assisted transluminal suture trabeculotomy

Abstract

We retrospectively investigated the relationship between Schlemm's canal incision length and the results of ab interno gonioscopy-assisted transluminal suture trabeculotomy (GATST) with/without cataract surgery in open-angle glaucoma patients at Tsukazaki Hospital from 2018-2021. The study included 113 eyes from 76 patients (age: 70.0 ± 10.8 years; female/male: 43 [56.6%]/33 [43.4%]). GATST with and without cataract surgery was performed on 87 (phakia) [77.0%] and 26 eyes (pseudophakia) [23.0%], respectively; 102 [90.3%] eyes had primary open-angle glaucoma, and 11 [9.7%] had pseudoexfoliation glaucoma. Intraocular pressure (IOP) significantly decreased at 3/6/12 months, and the antiglaucoma eyedrop number significantly decreased at 6/12 months (all P values < 0.001). Linear mixed-effects models showed that incision length had significant positive associations with IOP spikes, hyphema grade, and IOP changes (amount/percentage) at 6 months; surgical success rate (IOP ≤ 15 mmHg, ≥ 20% reduction, no additional surgeries [criterion B]) at 6/12 months; and surgical success rate (IOP ≤ 21 mmHg, ≥ 20% reduction, no additional surgeries [criterion A]) at 12 months (Ps < 0.05). There were no significant associations with IOP changes at 12 months, surgical success rate (criterion A) at 6 months, or antiglaucoma eyedrop number at either timepoint (Ps > 0.05). Longer incisions were more likely to produce greater IOP reduction, requiring more attention to IOP spikes/hyphema.

Keywords: Ab interno gonioscopy-assisted transluminal suture trabeculotomy (GATST); Minimally invasive or microinvasive glaucoma surgery (MIGS); Open-angle glaucoma; Schlemm’s canal incision length.

Fig. 1

Outcomes demonstrating a significant relationship with Schlemm’s canal incision length. The data are presented as estimated coefficients and 95% confidence intervals (CIs) for increasing Schlemm’s canal incision lengths for each outcome. The x-axis indicates the adjusted coefficients with 95% CIs. The whiskers indicate 95% CIs for point estimates. The models were adjusted for sex, age, glaucoma type, surgical type, number of antiglaucoma eye drops and preoperative IOP. Statistical significance (P) values are shown on the right. *p < 0.05, **p < 0.01.

Fig. 2

Scatter plots showing the relationship between Schlemm’s canal incision length and IOP changes.The y-axis indicates the model’s predicted IOP change. The predicted values were calculated from a model adjusted for sex, age, glaucoma type, surgical type, and number of antiglaucoma eye drops. The line represents the LOESS (locally weighted smoothing) curve fitted through the points in the scatter plots, illustrating trends between IOP change and incision width: the amount of IOP change at 6 M (a), the amount of IOP change at 12 M (b), the percentage of IOP change at 6 M (c), and the percentage of IOP change at 12 M (d).

Fig. 3

Change-point analysis to detect a threshold for Schlemm’s canal incision length associated with IOP spikes, hyphema grade, and surgical success rates.The line chart shows the trend between the p value and Schlemm’s canal incision length, with change points indicated by larger blue dots. The p values were calculated from a chi-square test assessing the IOP change, hyphema grade, and surgical success rate when the dataset was divided into two groups at a specific threshold. For the mean shift in the P value, horizontal red lines are drawn at the mean value of each segment: IOP spike (a), hyphema grade (b), surgical success rate (Criterion A) (c), and surgical success rate (Criterion B) (d).