In Vivo Structure of the Schlemm’s Canal and the Collector Channels in Eyes with Chronic Angle-Closure Glaucoma Compared to Normal Eyes

Abstract

 

Purpose

 

To characterize in vivo structure of the Schlemm’s canal (SC) and the collector channels (CC) in eyes with chronic angle-closure glaucoma (CACG) compared to normal eyes.

 

Methods

 

Serial horizontal enhanced depth imaging optical coherence tomography (EDI OCT) B-scans were obtained in the nasal and temporal limbal areas from CACG patients and normal subjects (81 scans per 15x5 degree rectangle; interval between scans, ~35 µm; Fig A and B). The cross-sectional area of the SC was measured in each EDI OCT B-scan (Fig C). After three-dimensional SC reconstruction, SC volume was calculated for each eye. The CCs connected to SC (Fig D) were counted.

 

Results

 

Nine CACG eyes (9 patients; mean age, 72±10 years) and 11 normal eyes (11 subjects; mean age, 28±5 years) were included. In CACG eyes, the SC and CC were mostly obliterated in the areas with high peripheral anterior synechiae (PAS; Fig E) and were mostly open but smaller than those in normal eyes in the areas with no or low PAS (Fig F). The mean cross-sectional SC area was significantly smaller in the CACG than in the normal eyes (863±611 µm² vs. 3512±1228 µm²; p<0.001; Fig G), as was the SC volume (0.005±0.003 mm³ vs. 0.020±0.006 mm³; p<0.001). The number of the CCs was significantly smaller in the CACG than in the normal eyes (2.3±1.3 vs. 6.5±1.6; p<0.001; Fig H).

 

Conclusions

 

SC appears smaller and connected to fewer open CCs in CACG eyes than in normal eyes. In CACG eyes, circumferential aqueous flow is compromised in areas with high PAS.

 

 

(A) 15x5 degree rectangle for 81 serial horizontal EDI OCT B-scans. (B) A horizontal EDI OCT B-scan of the limbus and sclera (red arrow = Schlemm’s canal [SC]). (C) SC was delineated (red dotted line) to measure its cross-sectional area (asterisk = scleral spur). (D) Yellow arrows = collector channel. (E) Obliterated SC (red arrows). (F) Open but small SC (red arrows) and CC (yellow arrows). (G and H) Box-and-whisker plot for the SC area and the number of collector channels in the CACG and the normal eyes.

 

Keywords: 419 anatomy • 421 anterior segment • 552 imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound)