Evaluation of circumferential angle closure using iridotrabecular contact index after laser iridotomy by swept‐source optical coherence tomography

Purpose To investigate the quantitative changes of circumferential angle closure after laser iridotomy ( LI ) using the iridotrabecular contact ( ITC ) index by Swept‐Source optical coherence tomography ( OCT ). Methods In this prospective observational study conducted in a hospital setting, 42 eyes of 36 patients (five males, 31 females) who underwent LI were included. The mean age was 65.00 ± 8.13 years old and the diagnosis included primary angle closure ( PAC , 21 eyes), PAC suspect (16 eyes) and PAC glaucoma (five eyes). Optical coherence tomography (OCT) images were obtained pre‐ LI and at 1 week post‐ LI . In each image frame, the scleral spur ( SS ) and the ITC end‐point were marked, from which the ITC index was calculated as a percentage of the angle closure across 360°. Measurements inspected before and after LI included: central anterior chamber depth ( ACD ), anterior chamber volume ( ACV ), lens vault ( LV ), nasal and temporal angle opening distance ( AOD ), angle recess area ( ARA ), trabecular‐iris space area ( TISA ), trabecular‐iris angle ( TIA ) at 500  μ m and 750  μ m from the SS and intraocular pressure ( IOP ). Results The ITC index and IOP decreased significantly after LI from 71.52 ± 26.29 to 35.31 ± 27.19 and from 20.64 ± 12.72 mmHg to 14.02 ± 3.49 mmHg, respectively (p < 0.001 and p < 0.001). Central ACD (1.94 ± 0.31 mm pre‐ LI ) and LV (1.13 ± 0.32 mm pre‐ LI ) did not show a significant change after LI (all p > 0.05), but ACV increased significantly after LI (p < 0.001). Most of the angle parameters except for nasal TIA s increased significantly after LI (all p < 0.05). Conclusion The ITC index from patients with shallow anterior chamber angle showed a significant decrease after LI , but part of the angle closure was not relieved after LI . Other mechanisms besides pupillary block may play a role together in causing angle closure.