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Jessica E. Nevins, Larry Kagemann, Ning-Jiun Jan, Ian A. Sigal, Gadi Wollstein, Hiroshi Ishikawa, Jonathan Grimm, Zach Nadler, Joel S. Schuman; Schlemm's Canal (SC) Cross-sectional Area (CSA) and Shape Fluctuation. Invest. Ophthalmol. Vis. Sci. 2012;53(14):2744.
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Individual cross-section measurements of SC may not adequately characterize its size and morphology due to structural fluctuations. The purpose of this study was to evaluate the rates of local fluctuation of CSA and circularity of SC.
Six eyes from six healthy volunteers were imaged using Bioptigen spectral-domain optical coherence tomography (Bioptigen Inc., Durham, NC). From a 4mm length segment (40 slices, each comprised of 700 a-scans) of SC, 1mm (10 slices) was selected that contained good visualization of SC throughout. The changes in cross-sectional area and shape of SC within 100µm were quantified sequentially (slice to slice) through the selected 1mm length, yielding 9 measurements per subject (Figure). The area measurement technique and its reproducibility have been described.1 Shape was automatically assessed by circularity (a morphology parameter; a continuous value from 0 = perfectly flat to 1 = perfect circle). Visualization was subjectively optimized and all measurements done in Fiji (ImageJ 1.45q, NIH, http://imagej.nih.gov/ij).
The average and standard deviation CSA and shape across all subjects were 4412.58 ± 2916.95µm2 and 0.42 ± 0.15, respectively. The average and standard deviation slice to slice change of CSA and shape across all subjects were 280.43 ± 1903.63µm2 and 0.00 ± 0.17, respectively. Individual subject's CSA, CSA slice to slice change, circularity, and circularity slice to slice change showed the same variability (Table).
Large variability was observed in size and shape in a very short distance along SC. Analysis of SC should include sampling from multiple locations to ensure the validity of the measurements.1Kagemann L, Wollstein G, Ishikawa H, et al. Identification and assessment of Schlemm's canal by spectral-domain optical coherence tomography. Invest Ophthalmol Vis Sci. Aug 2010;51(8):4054-4059.
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