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Sue Wei Ho, Mani Baskaran, Ce Zheng, Tin A. Tun, Arun Kumar Narayanaswamy, Shamira A Perera, David S. Friedman, Tin Aung; Reproducibility Of Swept Source Optical Coherence Tomography Measurement Of The Iris-trabecular Contact (ITC) Index: A New Parameter For Angle Closure. Invest. Ophthalmol. Vis. Sci. 2012;53(14):3264.
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To evaluate the inter- and intra-observer reproducibility of measurement of the iris-trabecular contact (ITC) index using swept source optical coherence tomography (SS-OCT; CASIA SS-1000 Tomey).
This was a prospective observational study. All subjects underwent a standardized ophthalmic examination including gonioscopy. SS-OCT scans of one randomly selected eye was captured under strict dark room conditions and constituted acquisition of 128 consecutive meridional scans along 360 degrees. Each eye was scanned 3 times by two experienced operators. Post imaging analysis involved the estimation of the ITC index, a semi-quantitative measure of the degree of angle closure of each imaged eye using in-built software in the imaging device. Sixteen images or frames were used for the measurement of ITC index (Figure 1). The inter- and intra- observer reproducibility was analyzed separately for image grading and image acquisition. Intra-class coefficient (ICC) and the Bland-Altman plot were used to evaluate the agreement between inter and intra-observer reproducibility of the ITC.
Twenty-nine patients (29/60 eyes, 48.3% of those enrolled) had angle closure in two or more quadrants on gonioscopy, with a mean age of 65.5 (Standard deviation [SD] 7.1). Study subjects were predominantly Chinese 54/60 (90%) and female (42/60, 70%). The intraclass correlation (ICC) for inter observer reproducibility of ITC was excellent [0.98 (95% confidence interval (CI) = 0.95-0.99)] and the mean difference (95% intervals of agreement) using Bland-Altman test was -0.8 (-7.3,5.7). The ICC for intra observer reproducibility of ITC index was 0.991 (95% CI = 0.96-1.00) and the mean difference and 95% intervals of agreement was -0.8 (-8.2,6.5). The ICC for inter examiner reproducibility of image acquisition was 0.97 (95% CI = 0.95- 0.98) and the mean difference by Bland Altman test was 0.3 (-13.4,13.9)
The inter- and intra-observer reproducibility of measurement of the ITC index was excellent using SS-OCT.
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