Assessment of Schlemm's canal in acute primary angle closure: an anterior segment optical coherence tomography study

To image and quantitatively evaluate the Schlemm's canal (SC) dimensions in the eyes with acute primary angle closure (APAC) with anterior segment optical coherence tomography (AS-OCT), and compare it with the SC measurements taken after the control of intraocular pressure (IOP) and in the normal age-matched controls.

Seventeen eyes of 14 patients with the newly diagnosed APAC and 59 age-matched normal subjects underwent AS-OCT to image SC. SC cross-sectional area, SC meridional and coronal diameters were measured in the temporal and nasal regions at 3 and 9 o'clock position. After laser iridotomy and control of the IOP, all SC parameters were measured again at a week later, in APAC eyes. Intrasession intraobserver reliability of the SC measurements was assessed with intraclass correlation coefficient.

Mean SC-SCA (10,600 ± 2691 µm²), SC meridional (682 ± 125 µm) and coronal diameters (21.2 ± 8.2 µm) showed a significant increase in the APAC eyes at presentation, when compared to the SC parameters measured at a week later (6499 ± 1754 µm², 450 ± 169 µm and 15.75 ± 8.6 µm, p = < 0.0001, < 0.0001 and 0.01, respectively) and in the normal controls (7192 ± 1022 µm², 499.2 ± 179.8 µm, 15.43 ± 4.35 µm, p = 0.02, < 0.0001, 0.01, respectively). There was no difference in the measured SC parameters between the normal controls and APAC eyes, when the parameters were measured at a week, after resolution of the acute attack (all p > 0.05).

A significant expansion of SC was observed in the APAC eyes at presentation, when compared to the normal controls and after the acute attack resolved. SC parameters may provide a useful research tool for evaluating morphological changes in the SC in APAC eyes, during an acute attack.