Background <p>Previous studies with advanced imaging like phase-sensitive optical coherence tomography suggest the trabecular meshwork–Schlemm’s canal complex may show subtle motion related to intraocular pressure fluctuations or cardiac rhythm. However, direct visualization of rhythmic motion in the Schlemm’s canal region during routine gonioscopy has been undocumented. Here, we report an incidental finding during dynamic gonioscopy, where a retained 10 − 0 suture within Schlemm’s canal exhibited subtle, regular back-and-forth movement at the 2-year follow-up after penetrating canaloplasty.</p> Case presentation <p>A 53-year-old man was diagnosed with chronic angle-closure glaucoma in both eyes and had a history of uveitis. His left eye had previously undergone trabeculectomy, but intraocular pressure remained poorly controlled, prompting a subsequent penetrating canaloplasty. During the procedure, a 10 − 0 suture was placed through Schlemm’s canal to enhance the conventional outflow pathway. Postoperative follow-up remained stable, and no further glaucoma surgery was needed. At the 2-year postoperative visit, gonioscopy during slit-lamp examination revealed a 10 − 0 suture crossing Schlemm’s canal at approximately 1 o’clock in the superior angle. Within a relatively stable visual field, the suture exhibited consistent, rhythmic back-and-forth movement, and this pattern was reliably observed throughout the same examination session. At that time, the anterior chamber was quiet and showed no signs of active inflammation.</p> Conclusion <p>This case reports an incidental gonioscopic finding of subtle, rhythmic movement of a retained 10 − 0 suture within Schlemm’s canal 2 years after penetrating canaloplasty. The retained suture may act as a visible marker of local dynamic behavior in Schlemm’s canal.</p>