Characteristics and variations of in vivo Schlemm's canal and collector channel microstructures in enhanced-depth imaging optical coherence tomography

Background/aims To characterise in vivo Schlemm's canal (SC) and collector channels (CC) microstructures using enhanced-depth imaging (EDI) optical coherence tomography (OCT). Methods Serial horizontal EDI OCT B-scans (81 scans, 15×5° rectangle) were prospectively obtained in the nasal and temporal limbus. SC cross-sectional area (CSA) was measured by delineating its lumen in each B-scan. CCs connected to SC were counted. SC CSA and the number of CCs were compared between the nasal and temporal areas. Results Eleven eyes (11 normal subjects) were included (mean age, 28±5 years). SC and CCs were clearly demarcated in EDI OCT B-scans with excellent repeatability and reproducibility (intraclass correlation coefficients, 0.830–0.886 and 0.793, respectively; all p<0.001). SC CSA varied considerably among subjects, ranging from 1664 to 6007 µm2 (average, 3514±1235 µm2), and among different regions of the same eye with coefficient of variation in each eye ranging from 23% to 46% (average, 32±7%). The number of CCs in the analysed area also varied considerably among subjects, ranging from 5 to 11 (average, 8.73±1.85). The mean SC CSA (3839±1402 µm2 vs 3189±1209 µm2; p=0.033) and number of CCs (5.5±1.4 vs 3.3±1.1; p=0.001) were significantly greater nasally than temporally. The mean SC CSA was significantly correlated with the number of CCs (r=0.635, p=0.036). Conclusions High-quality images of the aqueous outflow pathway can be obtained with a clinical device, avoiding postacquisition processing. In vivo SC and CC microstructures vary considerably among individuals and regions. SC tends to be larger in regions with more CCs.