Microarchitecture of Schlemm Canal Before and After Selective Laser Trabeculoplasty in Enhanced Depth Imaging Optical Coherence Tomography

Purpose:To characterize the in vivo effect of selective laser trabeculoplasty (SLT) on the Schlemm canal (SC) in eyes with primary open-angle glaucoma (POAG).Materials and Methods:Eighty-one serial horizontal enhanced depth imaging optical coherence tomograph B-scans (interval between B-scans, approximate to 35 m) of the nasal corneoscleral limbus were obtained before and 4 weeks after SLT. Fifty B-scans in the overlapping regions before and after SLT were selected for analysis based on the structures of aqueous and blood vessels as landmarks. The SC cross-sectional area (CSA) was measured in each selected B-scan and averaged to generate the mean SC CSA of the eye. SC volume in the overlapping region was calculated using commercially available 3-dimensional reconstruction software. The mean SC CSA and SC volume were compared between pre-SLT and post-SLT B-scans. Correlation analysis was performed between SC CSA changes and intraocular pressure (IOP) changes.Results:Thirteen POAG eyes (13 patients) were included for analysis (mean age, 68.29.2 y). After SLT, the mean IOP was reduced from 19.8 +/- 7.6 to 14.4 +/- 3.8 mm Hg (P=0.003); the mean SC CSA increased by 8%, from 2478 +/- 550 to 2682 +/- 598 m(2) (P=0.029); and the mean SC volume increased from 4,304,592 +/- 954,777 to 4,658,250 +/- 1,039,956 m(3) (P=0.029). Increase in SC CSA had a significant positive correlation with IOP reduction after SLT (P=0.023, R=0.622).Conclusions:SLT expands SC in POAG patients and even more so with greater IOP reduction after SLT. Post-SLT expansion of SC may be due to increased trabecular aqueous outflow, IOP decrease, or structural changes in trabecular meshwork resulting from SLT.