AIM: To evaluate the effect of ab-externo circumferential suture trabeculotomy(CST)on the 24 h pattern of intraocular pressure(IOP)in primary open angle glaucoma(POAG).

METHODS: This retrospective study included 18 POAG patients who had poor control of IOP from March 2021 to May 2022. The ab-externo CST was performed, and IOP was tested preoperatively and 1 a postoperatively(9:00 a.m., 12:00 a.m., 3:00 p.m., 6:00 p.m., 9:00 p.m., 12:00 p.m., 3 a.m., and 6:00 a.m.). The mean, peak, trough, and range of IOP, as well as the average diurnal-nocturnal IOP change were calculated and compared.

RESULTS: The 24 h IOP curves exhibited a decreasing trend during the diurnal period and an increasing trend during the nocturnal period, reaching a trough in the afternoon and peaking at night; the time of trough and peak IOP occurred several hours earlier compared to preoperative eyes. Postoperatively, the mean, peak, and trough IOP values were significantly lower compared to preoperative levels. The range of fluctuation showed no significant difference, while the average diurnal-nocturnal IOP change increased significantly.

CONCLUSION: CST could reduce IOP of patients with POAG, but could not change the range of IOP fluctuation. However, an increase in the average diurnal-nocturnal IOP change was observed, indicating that CST might not necessarily reduce diurnal-nocturnal IOP fluctuations.