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Eric L Crowell, Mark E Gold, Alice Chuang, Laura Baker, Robert M Feldman, Nicholas P Bell, Lauren S Blieden; Characterizing Angle Landmarks with Anterior Segment Optical Coherence Tomography. Invest. Ophthalmol. Vis. Sci. 2014;55(13):929.
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© ARVO (1962-2015); The Authors (2016-present)
Identify the presence/absence of 3 identifiable landmarks: trabecular meshwork (TM), TM interface, and a novel landmark termed Bell’s Layer (BL), which is a juxtatrabecular landmark visible on anterior segment optical coherence tomography (ASOCT)
This is a retrospective review of imaging data from prior IRB-approved studies. Horizontal images from 2D angle analysis scans using a CASIA SS-1000 (Tomey, Nagoya, Japan) were evaluated by a masked, experienced reader for presence/absence of TM, TM interface, and BL using the ACAI (Houston, TX) software. Only one eye was included per participant. Logistic regression was used to analyze the potential factors of age, gender, race, IOP, gonioscopy grade, angle location and history/presence of surgery on visibility of these structures.
A total of 173 horizontal images were included in this study. The mean age of participants was 52.4 (+15.6) years old with 114 female (66%) and 109 (63%) white. No factors were found to affect the visibility of BL; however, it is more visible in white and black (p<0.05) populations than Asians in paired comparison. It is also more likely to be visible in eyes with a gonioscopy grade of E than of A (P=0.047). Being female is 2.86 times (P=0.0069) and a nasal angle is 2.98 times (P=0.0003) more likely to have an invisible TM. Additionally, being female is 1.78 times (P=0.0314) and a nasal angle is 2.22 times (P=0.0021) more likely to have an invisible TM interface.
Gender and location in the angle are 2 factors affecting visibility of TM and TM interface, while BL is more visible in non-Asian populations and eyes with wide open gonioscopy. We have identified a novel ASOCT landmark adjacent to the TM interface (Schlemm’s canal) which has not previously been identified or described. Further study is needed to determine the pathophysiologic relevance. We hypothesize that BL may correlate with directionally aligned fibers seen surgically when entering Schlemm’s canal via an abexterno approach.
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