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Jyotsna Maram, Xiaojing Pan, Zhou Yuan Zhang, Muneeswar Nittala, Peggy Romano, Vikas Chopra, Srinivas Sadda; Reproducibility of Schwalbe’s Line identification using time-domain and spectral-domain OCT. Invest. Ophthalmol. Vis. Sci. 2013;54(15):83. doi: https://doi.org/.
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The purpose of this study was to evaluate the intra and inter grader reproducibility for identifying the location of Schwalbe’s line (SL) using time domain (TD) and spectral domain (SD) anterior segment optical coherence tomography (AS-OCT) imaging.
AS-OCT imaging of the anterior chamber angle was performed on 20 eyes of 10 healthy normal subjects. All subjects underwent imaging with both a TD-OCT (Visante AS OCT) and a SD-OCT (Cirrus HD-OCT) in a darkened room (1 foot candles at eye) without mydriatic drops using a standardized imaging protocol. For the Visante AS-OCT, both vertical and horizontally-oriented B-scans were obtained to image the nasal and inferior angles. For the Cirrus HD-OCT, a 5-line raster scan was obtained of the nasal angle. For intra-grader reproducibility assessments, images were re-graded by the same grader at a later date after random sorting of images to maintain masking. For inter-grader assessments, a second masked grader reviewed the images. For each case, the grader identified and marked the location of Schwalbe’s line and determined its coordinate location relative to the borders of the image.
The mean age of the normal subjects was 30±6 years, and all had open angles by biomicroscopy and by OCT. The mean anterior chamber angle (SS angle) was 46.6±6.8 degrees with the Visante OCT. For intra-grader reproducibility in SL identification, excellent agreement was observed for both the TD-OCT and SD-OCT. The Intraclass correlation coefficients (ICC) were 0.99, 0.96, and 0.99 for nasal TD-OCT, inferior TD-OCT, and SD-OCT respectively (p<0.001 for all). For inter-grader reproducibility, excellent agreement was observed for the SD-OCT (ICC=0.95) but was not quite as consistent overall for TD-OCT (nasal ICC=0.99, but inferior ICC=0.89).
The position of Schwalbe’s line can be reproducibly determined using both SD and TD anterior segment OCT. The visualization of the termination of the endothelial cell layer made possible by the high-resolution and sensitivity of SD-OCT likely contributed to the excellent precision and reproducibility of this methods. Though Schwalbe’s line is often not as well-seen with TD-OCT, this requiring estimation of its position, application of standardized reading center approaches still allow Schwalbe’s to be localized reproducibly.
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