Clinical context

In glaucoma, intraocular pressure reduction is important but remains a surrogate outcome. Clinical value also depends on preservation of the visual field and optic nerve, safety, the need for additional medication or surgery, and treatment adherence. Target pressure is individualized, so the same numerical change can carry different meaning at different disease stages and rates of progression.

What was studied

Ab-interno canaloplasty enlarges conventional outflow without a filtering bleb and can accompany phacoemulsification. This retrospective longitudinal cohort followed 40 eyes of 28 patients with primary open-angle glaucoma for up to four years after combined surgery. Mixed models assessed IOP and medication change. Kaplan–Meier analyses used IOP ≤18 mmHg as the main threshold, with sensitivity thresholds of ≤15 and ≤21 mmHg.

How the evidence was produced

A cohort study describes how outcomes are associated with an exposure or treatment in an observed clinical population. This design is useful for routine practice, uncommon events and longer follow-up, but it remains vulnerable to confounding by indication, baseline risk differences and missing data. An association should not automatically be interpreted as a causal effect.

Key result IOP changed significantly over time, global P=.009. The largest mean reduction occurred at one year: −1.71 mmHg, 95% CI −2.94 to −0.47, P=.003. The effect attenuated, although mean IOP remained numerically below baseline through year four. Medication burden fell by 1.48 at one year, 95% CI −1.85 to −1.10, P<.001, followed by gradual reintroduction. Corneal hysteresis increased and remained above baseline, P<.001. At four years, the probability of IOP ≤18 mmHg was 85%, while medication-free control was 10%. No sight-threatening complications occurred.

How to interpret the result

The study distinguishes pressure control from freedom from drops. Most eyes met the 18-mmHg threshold, but nine in ten required medication by four years. That is not necessarily failure because targets depend on stage and progression. Higher hysteresis is interesting but may influence tonometry and does not prove neuroprotection. The findings support realistic counseling about MIGS durability.

The result should be understood as an estimate for the population studied, not a promise of an individual outcome. Statistical and clinical significance, absolute and relative effects, and prespecified and exploratory analyses should be distinguished. When several endpoints or subgroups are reported, the prespecified primary endpoint for which the study was designed usually provides the most reliable inference.

Clinical applicability

The findings can inform discussions about treatment sequence and burden. Before changing management, compare the study population with the patient in front of you, including glaucoma stage, baseline pressure, previous treatment, angle anatomy and rate of field loss. A pressure measurement does not replace structural and functional follow-up.

Limitations

Without a phaco-only control, canaloplasty cannot be separated from lens extraction, regression to the mean or treatment changes. The sample was small, included fellow eyes and is vulnerable to four-year attrition. Threshold survival does not replace visual-field and nerve-OCT outcomes. Verify baseline IOP and drugs, glaucoma stage, eyes at each visit, restart criteria, tonometer, hysteresis effects, additional surgery, worst-case analyses, adverse events, funding and conflicts.

Beyond the limitations acknowledged by the authors, confidence is affected by sample size, follow-up duration, missing data, choice of comparator and relevance of the outcomes to routine care. Uncommon complications may remain undetected even in a well-conducted study. External validity is reduced when participants, equipment or investigator expertise differ substantially from everyday settings.

What to verify in the source

In the full paper, verify the protocol, eligibility criteria, baseline group characteristics, primary endpoint definition, confidence intervals, adverse events and losses to follow-up. Funding, conflicts of interest, trial registration and consistency between the published analysis and the original plan deserve separate attention. The DOI or source link below provides access to the primary publication for this check.