The Microachitecture of Schlemm’s Canal before and after Selective Laser Trabeculoplasty

Abstract

Purpose: To characterize the in vivo effect of selective laser trabeculoplasty (SLT) on the structure of Schlemm’s canal (SC) in open-angle glaucoma eyes.

Methods: Open-angle glaucoma patients with no other ocular or systemic diseases known to affect iridocorneal angle or trabecular aqueous outflow structures were prospectively recruited. Eighty-one serial horizontal enhanced depth imaging (EDI) optical coherence tomography (OCT) B-scans (interval between B-scans, ~35 µm) of the nasal corneoscleral limbal area were obtained before and 4 weeks after undergoing SLT in one eye of each patient. The EDI OCT B-scans in the overlapping area between the two sets of serial scans (before and after SLT) were selected for analysis using conjunctival vessels and iris anatomy as landmarks. The SC cross-sectional area was measured in each selected EDI OCT B-scan. After three-dimensional reconstruction, SC volume was determined.

Results: Eight eyes (3 men, 5 women; mean age, 64±10 years) were included. Mean intraocular pressure was 19.4±3.8 mmHg before the procedure and 16.8±5 mmHg after (p=0.17). Schlemm’s canal was continuous in the scanned area in all eyes and was successfully delineated and reconstructed 3-dimensionally pre- and post-operatively. Mean SC cross-sectional area did not change after SLT (6812±1654 µm² vs. 6687±1533 µm², respectively; p=0.44). Mean SC volume was also unchanged (11793990±2848340 µm³ vs. 11571340±2865261 µm³, repectively; p=0.43).

Conclusions: SLT does not affect SC dimensions in open-angle glaucoma patients, suggesting that the IOP reduction following SLT is caused by factors other than mechanical alteration of SC anatomy. Whether specific SC anatomic features are correlated with the amount of IOP reduction remains to be determined. An improved understanding of the SLT effect on microarchitecture of the trabecular outflow pathway in vivo in glaucoma patients, using EDI-OCT, may help better explain its mechanism of action and predict which patients might best benefit from the procedure.