PurposeMyopes have a higher risk for open-angle glaucoma; however, the reason is not clear. This study aims to explore the morphologic alterations of Schlemm's canal and trabecular meshwork size in highly myopic eyes. MethodsForty myopic eyes from 40 patients with high myopia and 40 control eyes from 40 subjects with low myopia, emmetropia or low hyperopia were enrolled. Optical coherence tomography (OCT) was used to image Schlemm's canal and trabecular meshwork size. The correlations between the morphological alterations of Schlemm's canal and trabecular meshwork, spherical equivalent refractive error, axial length, and intraocular pressure were analysed. ResultsSubjects with high myopia had a significantly larger Schlemm's canal diameter in the nasal (188.185.6m vs 127.4 +/- 46.7m, P<0.001), temporal (200.1 +/- 7.2m vs 147.6 +/- 68.1m, P=0.001) quadrants and average value (173.1 +/- 48.1m vs 137.3 +/- 39.6m, P=0.001), and larger Schlemm's canal area in the nasal (7333.2 +/- 3877.7m(2) vs 3833.2 +/- 2094.7m(2), P<0.001), temporal (7274.8 +/- 3247.4m(2) vs 4631.1 +/- 2431.9m(2), P<0.001) inferior (5512 +/- 2504.9m(2) vs 3922.6 +/- 1935.6m(2), P=0.003) quadrants and average value(6165.4 +/- 2080.5m(2) vs 4044.4 +/- 1581.1m(2), P<0.001). In the high myopia group, trabecular meshwork thickness of the nasal and temporal quadrants was significantly smaller (108.8 +/- 31.6m vs 126 +/- 42.2m, P=0.045; 100.5 +/- 15.4m vs 118.4 +/- 26.8m, P=0.001, respectively) compared with the control group, as well as the average value (106.4 +/- 16.5m vs 120.9 +/- 23.5m, P=0.002). In the high myopia group, Schlemm's canal and trabecular meshwork size were not correlated with spherical equivalent refractive error and axial length (P>0.05), while Schlemm's canal area showed a significant negative correlation with intraocular pressure (r=-0.33, P=0.039). ConclusionsThis study reports for the first time that eyes with high myopia have a larger Schlemm's canal diameter and area, as well as decreased trabecular meshwork thickness, which may help to understand the close association between high myopia and open-angle glaucoma. Schlemm's canal and trabecular meshwork analysis by OCT images may help to characterise the underlying pathophysiological mechanisms involved in high myopia.