This retrospective study used anterior segment (AS) OCT to identify Schlemm’s canal (SC), trabecular meshwork (TM), and a novel landmark identified as the band of extracanilicular limbal lamina, or BELL.
Study design
Imaging was performed in a dark room (0 lux) using a swept source-dedicated anterior segment OCT platform. Gonioscopy was performed on these patients and the Spaeth grading system was used. The images were read to identify scleral spur, Schwalbe’s line and Schlemm’s canal. Trabecular meshwork and BELL were also identified. Images were exported into customized software for additional analysis, and a trained reader was blinded to the patient’s known clinical characteristics or gonioscopic grade.
Logistic regression was performed to identify factors associated with the visibility of angle structures. Furthermore, the authors examined 5 enucleated eyes to analyze clinical-pathologic correlations.
Outcomes
A total of 153 eyes of 153 participants were included. Conventional markers such as TM and SC were identified in 73% and 40% of angles, respectively. However, BELL was found in 95% of angles and was more often detected in grade E than grade A eyes (98% vs. 83%, P=0.02). This landmark was identified in pathologic examinations as well. Landmark visibility was not affected by age, IOP or gender (P>0.05).
Temporal angles made it easier to identify TM and SC on AS OCT. Both were more visible in open angles than in narrow angles, but this finding was only significant for SC.
Limitations
Imaging was performed on horizontal angles, which may be easier to image than superior and inferior angles. Additionally, the pathologic evaluation was not age-matched to OCT correlates. The OCT images were obtained in a controlled, dark setting, and on a high-resolution swept-source anterior segment-dedicated OCT. This may have limited the generalizability of these findings, as most ophthalmologists do not have easy access to such imaging technology yet.
Clinical significance
This is the first time BELL was clearly identified. Previous studies merely characterized it as a TM shadow. Further studies are necessary to understand the significance of this structure.