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T. Aung, C. Zheng, C.-L. Ho, T. A. Tun, R. S. Kumar, T. Y. Wong, C. Y. Cheung; Novel Anterior Chamber Angle Measurements With High Definition Optical Coherence Tomography Using the Schwalbe’s Line as the Landmark. Invest. Ophthalmol. Vis. Sci. 2010;51(13):3855. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
To propose the Schwalbe’s line (SL) as a new anatomical landmark, independent of scleral spur (SS) location, for assessing anterior chamber angle (ACA) width quantitatively with high-definition optical coherence tomography (HD-OCT) (Cirrus, Carl Zeiss Meditec, Dublin, CA).
Seventy-three hospital-based subjects were recruited for this study. All subjects underwent standardized dark room gonioscopy (graded with the modified Shaffer system) and HD-OCT in one eye. To assess the ACA width quantitatively, we developed a computer program to define two new parameters using SL as the landmark: Schwalbe’s line-angle opening distance (SL-AOD) and Schwalbe’s line-trabecular-iris space area (SL-TISA), both measured at 500 µm from the SL. We also measured SS-parameters (SS-AOD and SS-TISA measured at 500 and 750 µm from the SS). The association between SL-parameters, SS-parameters and gonioscopic grading were evaluated, and area under the receiver operating characteristic curves(AUC) were used to assess the ability of SL- and SS-parameters to detect closed angles.
117 HD-OCT images from 73 subjects (47 female, 26 male) were used for analysis. The mean (standard deviation [SD]) age of the subjects was 60.6 (11.4) years. SL and SS could not be identified in 5% and 15% respectively of HD-OCT scans (p=0.035). The reproducibility of SL-measures was high (intraclass correlations ranged from 0.98 to 0.99). SL-AOD and SL-TISA were significantly correlated with SS-parameters (Pearson correlation coefficients ≥ 0.85, p<0.001) and gonioscopic width (Spearman’s correlation coefficient ≥ 0.69, p<0.001). The discriminative ability of SL-parameters in identifying open- and closed-angle groups was comparable to that of SS-parameters (all AUCs between 0.83-0.88, all p>0.05 comparing AUC between SL and SS parameters).
The SL can be identified in 95% of HD-OCT scans. Novel parameters, SL-AOD and SL-TISA measured by HD-OCT, may be useful to quantify the ACA width and to assess for angle closure.
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