180° versus 360° selective laser trabeculoplasty for the treatment of open glaucoma or ocular hypertension: a systematic review and meta-analysis of randomized controlled trials

Introduction

Glaucoma is a leading cause of blindness worldwide, second only to cataract (1). It is characterized by a neurodegenerative condition that affects the optic nerve, marked by deterioration of retinal ganglion cells and visual field loss (2). The only method for treating glaucoma is controlling intraocular pressure (IOP), critical for slowing or arresting disease progression (2).

Open-angle glaucoma (OAG), the most common subtype, has traditionally been treated through laser and topical therapy, followed by surgery for advanced cases (3-5). While IOP-lowering eyedrops are effective, they pose significant challenges, particularly for the elderly, due to difficulties in administration, side effects, and the financial burden (6-10). Alternatively, selective laser trabeculoplasty (SLT) has been successfully used for IOP control, increasing the aqueous outflow through the trabecular meshwork (11). The laser selectively targets pigmented cells and avoids thermal damage to adjacent non-pigmented structures, facilitating aqueous filtration into the venous system without causing significant structural harm (12,13). As outlined by Rolim-de-Moura et al. in a Cochrane review, SLT has demonstrated comparable efficacy to medications at a lower cost without serious unwanted effects (14).

SLT has been integrated into treatment algorithms and recommended as a first-line therapy for OAG and ocular hypertension (OHT) (15,16). Nevertheless, there is still no consensus on the optimal SLT protocol (14,17,18). Initially, SLT was performed on 180° of the trabecular meshwork, but many ophthalmologists now favor the 360° treatment, hypothesizing greater efficacy (19,20). Previous randomized controlled trials (RCTs) investigated the relative efficacy and safety of these methods. Yet, their conclusions differed, possibly owing to small sample sizes and distinct patient characteristics (5,20-23).

Two recent meta-analyses addressed the same comparison (24,25). Both concluded that 360° SLT provides superior IOP reduction and higher success rates versus 180° SLT. However, these reviews included randomized and retrospective studies, which introduced heterogeneity in design and potential confounding, and limited the quality of evidence to low-moderate.

Having in mind the increase in the use of SLT as the first treatment option and the need for evidence-based indications regarding optimal SLT protocols, this systematic review and meta-analysis with trial sequential analysis (TSA) of RCTs aimed to assess the efficacy and safety of 180° versus 360° SLT for the treatment of OAG or OHT, with IOP as the primary endpoint. We present this article in accordance with the PRISMA reporting checklist (available at https://aes.amegroups.com/article/view/10.21037/aes-25-57/rc).

Methods

This study followed the Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) guidelines (26). The protocol was registered in the International Prospective Register of Systematic Reviews (PROSPERO) as CRD42024532110.

Eligibility criteria

Eligibility criteria comprised (I) RCTs; (II) comparing 180° with 360° SLT in patients with OAG or OHT; and (III) reporting at least one outcome of interest. We excluded conference abstracts. There were no restrictions concerning the language of publication.

Search strategy

Two authors (M.P.C., T.F.N.) conducted the literature search on PubMed, Cochrane Library, Embase, and Web of Science for records published from inception to November 8, 2025. Search strings consisted of Boolean combinations of the following terms: “randomized”, “randomised”, “random”, “clinical”, “controlled”, “trial”, “laser”, “slt”, “trabeculectomies”, “trabeculoplasty”, “trabeculoplasties”, “trabeculotomy”, “trabeculotomies”, “goniotomy”, “goniotomies”, “glaucomas”, “glaucoma”, “open-angle”, “compensated”, “pigmentary”, “simple”, “simplex”, "simplices”, “compensative”, “primary”, “secondary”). Detailed search strings are available in Table S1. References of included studies were searched for further studies. The senior author (T.T.d.S.) resolved any controversies about study eligibility.

Endpoints

The primary endpoint was IOP, assessed at 1 day, 1 week, 1 month, 3 months, 6 months, and 12 months post-operatively. Secondary endpoints, evaluated at the last follow-up of each study (27), comprised treatment success, visual acuity, adverse events, postoperative inflammation, and pain or discomfort. While preserving unmanipulated data, we evaluated treatment success according to each study’s original definition.

Data extraction

Two investigators (M.P.C. and E.P.) independently extracted the following data: number of patients; mean age; time since diagnosis; follow-up; treatment regimens; SLT’s energy per spot, number of spots, and total energy; IOP-lowering therapy at baseline; and endpoints. We performed an intention-to-treat analysis when data was available. A third reviewer (R.O.M.F.) double-checked data collection.

We combined the standard and high energy arms in intervention and control groups from one study because a subgroup analysis was not possible (20,27). The Cochrane Handbook for Systematic Review of Interventions was used for data handling and conversions (28). Accordingly, we imputed missing standard deviations (SDs) of IOP reported by one study using the arithmetic mean of the other studies’ SDs for that same endpoint (21). We used the WebPlotDigitizer to extract graphical data (29).

Risk of bias assessment

Two authors (M.P.C. and E.P.) conducted the risk of bias assessment. The senior author (T.T.d.S.) resolved any disagreements. The risk of bias was assessed according to the Cochrane risk-of-bias tool for Randomized Trials (RoB 2) (30). High risk of bias was assigned to studies with a high risk in any domain; some concerns were assigned to studies presenting some concerns in any domain, and low risk of bias if otherwise.

Publication bias assessment by funnel plot or Egger’s test was not conducted due to insufficient studies (n<10). Using these methods to evaluate publication bias would result in statistically underpowered and potentially misleading results (31).

Sensitivity analyses

We performed leave-one-out sensitivity analyses by removing each study at a time from meta-analyses and reanalyzing pooled effect sizes to test the consistency of results and identify sources of heterogeneity (32).

In addition, we conducted random effects meta-regressions to explore the influence of moderators (age, baseline IOP, energy per spot, sex, OHT diagnosis, treatment-naive patients, number of IOP-lowering medications at baseline, pseudoexfoliation, and race) on the IOP endpoint (32).

Quality of evidence

We classified the quality of evidence according to the Grading of Recommendation, Assessment, Development and Evaluations (GRADE) guidelines (33). Endpoints received a score of very low, low, moderate, or high quality evidence based on risk of bias, inconsistency of results, imprecision, indirectness, and effect sizes.

TSA

TSA assessed whether the cumulative evidence in the primary endpoint (IOP) was powered to detect a beneficial effect of the intervention with 90% power at the 0.05 significance level. The conventional boundary (with α error of 5%), the trial sequential monitoring boundaries (TSMBs), and the cumulative sequential z-score curve were plotted to compare 180° and 360° SLT. The number of participants needed to detect intervention effects was estimated based on the DerSimonian–Laird random-effects model (34).

Statistical analysis

We estimated weighted mean differences (MDs) and risk ratios (RRs) with 95% confidence intervals (CIs) for continuous and binary endpoints, respectively, with a random-effects model (35). The 360° SLT was used as the control group. We assessed between-study heterogeneity using the Cochrane Q-test and I² statistic; P<0.10 was considered significant for heterogeneity, and I² was interpreted according to the following thresholds: 0–40% might not be important; 30–60% may represent moderate heterogeneity; 50–90% may represent substantial heterogeneity; and 75–100% considerable heterogeneity (35).

We conducted statistical analyses using the R statistical software, version 4.2.3 (R Foundation for Statistical Computing), and the TSA software (Copenhagen Trial Unit, Centre for Clinical Intervention Research, Copenhagen). Outcomes of interest from individual studies were displayed in forest plots or described when reported by only one study.

Results

Study selection and characteristics

Our search strategy yielded 1,724 articles, as exhibited in Figure 1. After removing duplicate records and ineligible studies through title and abstract review, we thoroughly reviewed 24 articles. Finally, six studies were included, comprising 713 patients and 892 eyes (5,20-23,36). A total of 353 and 391 eyes were assigned to 180° and 360° SLT, respectively, and the follow-up ranged from 1 to 12 months. The mean age ranged from 54 to 72 years. Mean baseline IOP ranged from 17.1 to 29.3 mmHg, and the mean baseline number of IOP-lowering medications ranged from 0 (newly diagnosed) to 2.4. Baseline characteristics and treatment parameters are shown in Tables 1,2. Inclusion and exclusion criteria of included studies are detailed in Table S2.

Figure 1 PRISMA flow diagram of study screening and selection.

Pooled analysis of all studies

Primary endpoint

IOP at 1 day (MD 0.10 mmHg; 95% CI: −0.59 to 0.79; P=0.77; I²=0%; Figure 2A) and 1 week post-operatively (MD −0.44 mmHg; 95% CI: −0.36 to 1.25; P=0.28; I²=0%; Figure 2B) was not significantly different between groups. However, 180° SLT was associated with a significantly higher IOP at 1 month (MD 1.17 mmHg; 95% CI: 0.52–1.81; P<0.01; I²=36%; Figure 2C), 3 months (MD 0.96 mmHg; 95% CI: 0.45–1.47; P<0.01; I²=0; Figure 2D), 6 months (MD 1.03 mmHg; 95% CI: 0.14–1.92; P=0.02; I²=58%; Figure 2E), and 12 months (MD 1.63 mmHg; 95% CI: 0.66–2.60; P<0.01; I²=0; Figure 2F).

Figure 2 Forest plots of comparison between 180° SLT and 360° SLT for intraocular pressure at different time points in patients with open-angle glaucoma or ocular hypertension. (A) 1 day; (B) 1 week; (C) 1 month; (D) 3 months; (E) 6 months; (F) 12 months. CI, confidence interval; IV, inverse-variance; SD, standard deviation; SLT, selective laser trabeculoplasty.

Secondary endpoints

The 180° SLT group had a significantly lower treatment success ratio compared with the 360° SLT group (RR 0.72; 95% CI: 0.58–0.90; P<0.01; I²=50%; Figure 3A). Visual acuity (MD −0.002 logMAR; 95% CI: −0.029 to 0.026; P=0.90; I²=41%; Figure 3B) and the risk of adverse events (RR 1.08; 95% CI: 0.69–1.68; P=0.75; I²=0; Figure 3C) were not significantly different between groups. The risk of pain or discomfort was significantly lower with 180° SLT (RR 0.63; 95% CI: 0.50–0.81; P<0.01; I²=0; Figure 3D).

Figure 3 Forest plots of comparison between 180° SLT and 360° SLT for the treatment of open-angle glaucoma or ocular hypertension. (A) Treatment success; (B) visual acuity (logMAR); (C) adverse events; (D) pain or discomfort. CI, confidence interval; IV, inverse-variance; MH, Mantel-Haenszel; SD, standard deviation; SLT, selective laser trabeculoplasty.

No quantitative assessment of uveitis risk could be established due to the lack of events in two of three studies that assessed the endpoint (5,23). Nagar et al. reported 20 (40.8%) cases of uveitis with 180° SLT and 22 (50%) with 360° SLT (P>0.05) (21).

Sensitivity analyses

Sensitivity analyses are shown in Figures S1-S3. No outliers were identified. A change in the P value of IOP during leave-one-out tests was observed only at 6 months, resulting in non-significant differences between groups with the removal of Nagar et al. (MD 0.77 mmHg; 95% CI: −0.41 to 1.94; I²=68%), Özen et al. (MD 1.00 mmHg; 95% CI: −0.29 to 2.30; I²=70%) or Dahlgren et al. (MD 0.73 mmHg; 95% CI: −0.51 to 1.97; I²=63) (20,21,23). The elimination of Tufan et al. from this endpoint abolished heterogeneity while maintaining a significant difference in favor of 360° SLT (MD 1.41 mmHg; 95% CI: 0.83–1.99; I²=0%) (36). This might be explained by the case-series design.

The heterogeneity in treatment success was significantly decreased with the elimination of the study by Dahlgren et al., preserving a significant difference in favor of 360° SLT (20).

The pain or discomfort rate was similar between groups with the removal of Dahlgren et al., which might be linked to the use of high energy (RR 0.55; 95% CI: 0.29–1.05; I²=0%) (20). No significant changes in other endpoints were observed during leave-one-out tests.

Meta-regression

The percentage of eyes with OHT diagnosis was a positive moderator for the difference between 180° and 360° SLT, while the percentage of eyes with glaucoma was a negative moderator (P=0.03).

Studies with older participants tended to show larger differences between 180° and 360° SLT. Each 1-year increase in participants’ mean age was associated with a 0.1 mmHg increase in the MD between 180° and 360° SLT.

The P values for baseline IOP, energy per spot, proportion of women, treatment-naive patients, number of hypotensive medications at baseline, pseudoexfoliation, and Caucasian or African/Afro-Caribbean individuals were non-significant (P>0.05), suggesting that these factors did not influence the MD between 180° versus 360° SLT on IOP. Meta-regression is exhibited in Figures S4-S7.

Risk of bias assessment

A low risk of bias was assigned to all studies (Figure 4) (5,20-23,36).

Figure 4 Risk of bias assessment with the RoB 2. RoB 2, Cochrane Risk-of-Bias tool for randomized trials (version 2).

Quality of evidence

According to the GRADE assessment, six endpoints were classified as high-quality evidence: IOP at 1 day, 1 week, 1 month, and 3 months, treatment success, and pain or discomfort. Four endpoints had moderate quality of evidence: IOP at 6 and 12 months, visual acuity, and adverse events. The main domains responsible for decreasing the quality of evidence were imprecision and inconsistency. The summary of findings is available online: https://cdn.amegroups.cn/static/public/aes-25-57-1.pdf.

TSA

The z-curve of IOP crossed the 95% boundary for a significant effect and reached the required information size, suggesting that firm evidence exists for the benefit of 360° SLT over 180° SLT. The TSA graph for IOP is presented in Figure S8.

Discussion

This systematic review and meta-analysis with TSA of six RCTs comprising 892 eyes compared 180° with 360° SLT in patients with OAG or OHT. The main findings demonstrate a consistent disadvantage of 180° SLT on IOP compared with 360° SLT, accompanied by lower treatment success and no difference in the risk of adverse events, though lower risk of pain or discomfort.

The therapeutic focus for OAG relies on decreasing IOP to target levels (2). Although our results indicate that IOP did not differ between groups in the initial weeks, 180° SLT exhibited lower efficacy compared with 360° SLT from 1 month up to 12 months of follow-up. Previous RCTs report distinct findings. Nagar et al. analyzed 93 eyes and found no differences between groups in ≥20% or ≥30% IOP reduction without additional IOP-lowering therapy (21). Similarly, Goyal and colleagues reported comparable IOP change and ≥20% IOP decrease between 180° and 360° SLT (22). However, recent trials indicate a higher SLT performance by treating 360° of the trabecular meshwork at 6 months and 1 year post-operatively (5,20). Our analyses of IOP support this superior efficacy with moderate to high-quality evidence. At the 2-year follow-up, retrospective studies yielded comparable IOP reductions, with pure values (37,38) or at ≥20% marks (39). Whether our findings are sustained over the long term remains to be confirmed by large, high-quality RCTs.

The variability among studies could be accounted for by age and OHT diagnosis in meta-regression, implying that the effect size of 180° on IOP may be reduced compared with 360° SLT in older patients or those with OHT; that is, the 360° method yields an IOP even lower in these cases. A post hoc analysis of one included RCT aimed to identify factors influencing SLT efficacy and found no impact of age or glaucoma diagnosis on overall SLT performance (40). However, they observed that baseline IOP and the response to previous SLT were positive predictors of greater IOP reduction, and that central corneal thickness, pseudoexfoliation syndrome, and the number of prior SLTs were negative predictors. Importantly, they did not assess whether these characteristics moderated the treatment effect disparity between the 180° and 360° protocols, as in our analysis.

Beyond the extension of laser treatment on the trabecular meshwork, the power also exerts a role in achieving optimal performance. SLT is typically initiated at 0.8 mJ per treatment spot, with energy titrated to 0.1 mJ below the threshold of champagne-sized cavitation bubble formation (standard energy) (19). The recent optimal SLT (OSLT) trial indicated significantly improved and timely consistent IOP reductions with 360° SLT at an energy level sufficient to generate cavitation bubbles in 50% to 75% of laser spots (high energy) compared to both 360° SLT with standard energy and 180° SLT with standard or high energy (20). Despite our meta-regression showed no association between laser power and differences between 180° and 360° SLT on IOP, this could be explained by only one included study investigating high-energy, limiting statistical power.

The effect of SLT decreases with time, and its safe and effective repeatability provides an alternative to medical therapy for long-term disease management (41). Paula et al., in a real-world study including 45 eyes, reported that primary 180° SLT was associated with a higher IOP-lowering effect than repeated applications, even when the laser was applied to the untreated opposite anterior chamber angle (42). In a previous RCT, IOP response to repeat 180° SLT over previously treated eyes with 360° SLT was found to be half of the initial treatment (43).

Conversely, repeat 360° SLT has been associated with consistent IOP control to levels achieved by initial treatment (41,44-52), even after the third procedure (53). The consistent beneficial outcomes of primary 360° SLT and long-standing effects in repeat procedures may lead to less need for interventions and additional laser damage to the trabecular meshwork, compared with 180° SLT.

The state-of-the-art treatment of glaucoma involves not only achieving a favorable IOP but also managing adverse effects, quality of life, and, therefore, treatment compliance. The Laser in Glaucoma and Ocular Hypertension (LiGHT) study demonstrated that eyes in the 360° SLT arm achieved a 71.9% drop-free rate at target IOP compared with 23% in the medical arm at 6 years of follow-up (45). This result implies a positive impact on treatment adherence, given that medical therapy commonly requires multi-drop regimens due to the progressive nature of glaucoma and is associated with persistent undesired reactions (54-56). Likewise, the choice of sub-optimal laser treatment could lead to faster disease progression, demand more medications and invasive interventions, impacting treatment adherence.

In our study, ocular discomfort or pain was significantly lower with 180° SLT; these were mild and occurred only during the first week post-SLT. However, the risk of overall adverse events was similar between groups. Hence, as many patients would probably tolerate transient, minor adverse reactions in pursuing higher efficacy (20), 360° SLT could be highly desirable to control the need for adjunctive medical therapy and improve treatment satisfaction (54,57).

In TSA, firm evidence favoring the intervention is attained when the z-curve crosses the TSMB or the number of patients in the study reaches or exceeds the required sample size (33,34). The significant effects favoring 360° SLT in meta-analyses of IOP were corroborated by robust evidence of benefit in TSA, as the z-curve crossed the 95% boundary for a significant effect, and the number of patients attained the required sample size.

Clinical guidelines currently lack strong or high-quality evidence supporting the use of 360° SLT over 180° SLT (17,18,58,59). Furthermore, ophthalmologists may often rely on personal judgment when determining SLT techniques, and treating 180° of the trabecular meshwork remains a common practice (5,60). In light of this, our findings support the 360° method as a superior choice compared with 180° SLT for treating OAG or OHT.

This study has limitations. First, only six studies with short to medium follow-ups met eligibility criteria. Second, there was moderate heterogeneity in some endpoints, such as IOP. However, we performed meta-regression and found a significant association between age and OHT or glaucoma diagnosis on IOP. Furthermore, consistent results were observed during sensitivity analyses, suggesting an influence of the different study designs and eligibility criteria on heterogeneity. Third, IOP at 6 and 12 months was classified as moderate quality evidence due to inconsistency and imprecision, respectively. Notably, Tufan et al.’s study was responsible for the inconsistency observed in the six-month endpoint, which might be explained by the case-series design (36). Finally, three studies excluded eyes with pigmentary glaucoma.

Conclusions

180° SLT was associated with higher IOP from 1 month through 12 months of follow-up and lower treatment success compared with 360° SLT in patients with OAG or OHT. Although discomfort or pain was lower with the 180° protocol, the overall risk of adverse events was similar between groups. These findings indicate that 360° SLT provides superior short to medium-term efficacy. However, additional large, long-term RCTs are needed to clarify the durability of these results.

Acknowledgments

None.

Footnote

Reporting Checklist: The authors have completed the PRISMA reporting checklist. Available at https://aes.amegroups.com/article/view/10.21037/aes-25-57/rc

Peer Review File: Available at https://aes.amegroups.com/article/view/10.21037/aes-25-57/prf

Funding: None.

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://aes.amegroups.com/article/view/10.21037/aes-25-57/coif). The authors have no conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

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