Schlemm's canal and trabecular meshwork morphology in high myopia.

Abstract

Myopes 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. Forty 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. Subjects with high myopia had a significantly larger Schlemm's canal diameter in the nasal (188.1±85.6μm vs 127.4±46.7μm, P<0.001), temporal (200.1±7.2μm vs 147.6±68.1μm, P=0.001) quadrants and average value (173.1±48.1μm vs 137.3±39.6μm, P=0.001), and larger Schlemm's canal area in the nasal (7333.2±3877.7μm2 vs 3833.2±2094.7μm2 , P<0.001), temporal (7274.8±3247.4μm2 vs 4631.1±2431.9μm2 , P<0.001) inferior (5512±2504.9μm2 vs 3922.6±1935.6μm2 , P=0.003) quadrants and average value(6165.4±2080.5μm2 vs 4044.4±1581.1μm2 , P<0.001). In the high myopia group, trabecular meshwork thickness of the nasal and temporal quadrants was significantly smaller (108.8±31.6μm vs 126±42.2μm, P=0.045; 100.5±15.4μm vs 118.4±26.8μm, P=0.001, respectively) compared with the control group, as well as the average value (106.4±16.5μm vs 120.9±23.5μm, 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). This 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.