Trabeculectomy Slows Visual Field Loss Better Than Medication in Advanced Glaucoma

The Disconnect Between Perimetric Stability and Patient Function in Advanced Glaucoma

Managing patients with advanced open-angle glaucoma presents a significant clinical challenge, as late diagnosis is frequently associated with lower socioeconomic status and severe functional impairment at presentation [1, 2]. While topical medications and laser trabeculoplasty (a procedure using light energy to improve aqueous humor outflow) are standard for early disease, advanced cases often require incisional surgery to achieve the low intraocular pressures necessary to arrest disease progression [3, 4]. Primary trabeculectomy, a surgical intervention that creates a new drainage pathway for fluid, is often utilized to preserve visual function in these high-risk individuals [5]. However, the extent to which slowing the rate of visual field loss translates into measurable improvements in patient-reported quality of life remains a subject of ongoing clinical investigation [6]. A recent multicenter trial now clarifies the long-term comparative effectiveness of these management strategies, revealing a complex relationship between objective perimetric stability and subjective patient function.

Trial Design and Patient Characteristics

The Treatment for Advanced Glaucoma Study (TAGS) was a multicenter randomized clinical trial conducted across 27 secondary care glaucoma departments in the United Kingdom. The study enrolled 453 adults with newly diagnosed advanced open-angle glaucoma in at least one eye, with recruitment occurring between June 3, 2014, and May 31, 2017. For the purposes of analysis, the researchers identified one eligible index eye per participant, defined as the eye meeting the specific study inclusion criteria for advanced disease. Participants were randomized to receive either primary trabeculectomy (n = 227) or medical management (n = 226) as their initial treatment strategy. Baseline characteristics were similar between the trabeculectomy and medical management arms, ensuring a balanced comparison of the two intervention pathways from the outset of the five-year follow-up period. To evaluate the longitudinal data, the researchers utilized a validated Bayesian longitudinal hierarchical model (a statistical framework that accounts for individual patient variability and the specific structure of data collected over multiple time points). The final analysis included 442 patients who provided reliable visual field data, defined as a false positive rate of less than 15 percent, or 25-item Visual Function Questionnaire (VFQ-25) data from at least two separate time points. Within this analyzed cohort, 221 patients were in the trabeculectomy-first arm, providing a robust sample size to compare the rate of change in monocular index-eye visual fields and patient-reported quality of life outcomes against the medical management group.

Superior Visual Field Preservation with Primary Surgery

The primary clinical finding of the trial indicates that trabeculectomy more effectively reduced the rate of visual field loss compared to medical treatment in advanced glaucoma. Over the five-year follow-up period, the rate of index-eye visual field loss was -0.75 dB/year (95% Credible Interval [CrI], -0.90 to -0.59) in the medications-first arm. By comparison, the rate of index-eye visual field loss was significantly slower in the trabeculectomy-first arm, measuring -0.37 dB/year (95% CrI, -0.53 to -0.22). The difference in the rate of index-eye visual field loss between these two treatment groups was statistically significant (p = 0.002). For the practicing ophthalmologist, this confirms that initial surgical intervention provides superior preservation of monocular sensitivity in patients presenting with advanced disease. Despite the clear advantage of surgery in the index eye, the results for the binocular integrated visual field (a calculated measure of the combined visual field from both eyes) were less definitive. The researchers observed that differences between treatment groups for binocular integrated visual field decline were not statistically significant (p = 0.062). This lack of significance in the binocular measure, which more closely reflects how a patient uses their vision in daily life, may explain why the objective improvements in monocular visual field stability did not translate into a measurable difference in patient-reported quality of life scores between the two cohorts.

The Quality of Life Paradox

The primary outcome measures of the study included the mean difference in the rate of change in the monocular index eye visual field using the 24-2 SITA Standard (a widely used automated perimetry algorithm that tests the central 24 degrees of vision), the binocular integrated visual field, and the 25-item Visual Function Questionnaire (VFQ-25) composite score over five years. Despite the surgical group showing superior monocular preservation, differences between treatment groups for VFQ-25 composite score change were not statistically significant (p = 0.392). This finding suggests that the objective slowing of visual field decay in the more severely affected eye does not necessarily result in a perceptible improvement in a patient's daily life as measured by standard instruments. The researchers noted that the VFQ-25 may lack the sensitivity or reactivity required to capture the benefits of monocular interventions in a population that already has advanced disease. The study explored the relationship between objective vision loss and subjective experience by examining correlations between visual field measures and quality of life. At baseline, the correlation between the binocular integrated visual field and quality of life was 0.41 (95% Credible Interval [CrI], 0.32 to 0.49; p < 0.001), while the correlation between the index eye visual field and quality of life was lower at 0.22 (95% CrI, 0.12 to 0.32; p < 0.001). These baseline figures indicate that a patient's overall functional status is more closely tied to their combined binocular vision than to the status of their most affected eye. Longitudinal data further reinforced this connection, as the correlation between the rate of change in binocular integrated visual field and quality of life was 0.56 (95% CrI, 0.41 to 0.70; p < 0.001). In contrast, the correlation between the rate of change in the index eye visual field and quality of life was 0.43 (95% CrI, 0.26 to 0.58; p < 0.001). Despite a moderately strong correlation with the binocular integrated visual field, there was no difference in measured quality of life between treatment arms. For the practicing clinician, these data suggest that while trabeculectomy is more effective at slowing monocular progression, the clinical impact on patient-reported outcomes may be muted if the better-seeing eye remains stable or if the binocular field does not show a corresponding significant divergence between treatment groups.

Limitations of Current Patient-Reported Outcome Measures

The researchers concluded that the 25-item Visual Function Questionnaire (VFQ-25) may lack the necessary reactivity or sensitivity to detect the clinical impact of monocular glaucoma interventions. In the context of the Treatment for Advanced Glaucoma Study, which followed 453 adults with newly diagnosed advanced open-angle glaucoma, the tool failed to reflect the objective benefits of surgical intervention. Although trabeculectomy more effectively reduced the rate of visual field loss compared to medical treatment, the VFQ-25 composite score did not show a statistically significant difference between the two arms (p = 0.392). This suggests that the instrument may not be granular enough to capture changes in quality of life when the treatment is focused on a single index eye, particularly in a patient population that already presents with advanced functional impairment. For the practicing clinician, these findings highlight a significant discrepancy between objective perimetric preservation and subjective patient reporting. While the study demonstrated that the correlation between the rate of change in the binocular integrated visual field and quality of life was moderately strong at 0.56 (95% Credible Interval, 0.41 to 0.70; p < 0.001), the VFQ-25 remained unresponsive to the specific slowing of monocular decay achieved through surgery. The authors suggest that the VFQ-25 may not be reactive or sensitive enough to detect the impact of monocular glaucoma interventions, potentially masking the functional value of preserving the visual field in the more severely affected eye. Consequently, physicians should recognize that while trabeculectomy provides superior objective stabilization of the visual field, current patient-reported outcome measures may require more nuanced or sensitive assessment tools to fully reflect the clinical benefits of surgical management in advanced cases.

References

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2. King AJ, Hudson J, Fernie G, et al. Baseline Characteristics of Participants in the Treatment of Advanced Glaucoma Study: A Multicenter Randomized Controlled Trial.. American journal of ophthalmology. 2020. doi:10.1016/j.ajo.2020.01.026

3. Salamanca O. Comment on: “Systematic Review of Economic Evaluations in Primary Open-Angle Glaucoma: Decision Analytic Modeling Insights”. 2020. doi:10.1007/s41669-020-00224-9

4. Philippin H, Matayan E, Knoll K, et al. Selective laser trabeculoplasty versus 0·5% timolol eye drops for the treatment of glaucoma in Tanzania: a randomised controlled trial. The Lancet Global Health. 2021. doi:10.1016/s2214-109x(21)00348-x

5. King A, Hudson J, Fernie G, et al. Primary trabeculectomy for advanced glaucoma: pragmatic multicentre randomised controlled trial (TAGS). BMJ. 2021. doi:10.1136/bmj.n1014

6. Montesano G, Ometto G, Cheloni R, et al. Longitudinal visual field and quality of life change in the Treatment for Advanced Glaucoma Study.. Ophthalmology. 2026. doi:10.1016/j.ophtha.2026.04.020