Swept source optical coherence tomography measurement of the iris–trabecular contact (ITC) index: a new parameter for angle closure

• Published in: Graefe's archive for clinical and experimental ophthalmology 2013-04, Vol.251 (4), p.1205-1211
• Main Authors: Ho, Sue-Wei, Baskaran, Mani, Zheng, Ce, Tun, Tin A., Perera, Shamira A., Narayanaswamy, Arun K., Friedman, David S., Aung, Tin
• Format: Article
• Language: English
• Subjects: Aged; Area Under Curve; Female; Fourier Analysis; Glaucoma; Glaucoma, Angle-Closure - classification; Glaucoma, Angle-Closure - diagnosis; Gonioscopy; Humans; Imaging, Three-Dimensional; Iris - pathology; Male; Medicine; Medicine & Public Health; Middle Aged; Observer Variation; Ophthalmology; Prospective Studies; ROC Curve; Tomography, Optical Coherence; Trabecular Meshwork - pathology
• ISSN: 0721-832X; 1435-702X
• DOI: 10.1007/s00417-012-2158-6

Purpose To evaluate the inter- and intra-observer agreement of measurement of the iris–trabecular contact (ITC) index, a measure of the degree of angle closure, using swept source optical coherence tomography (SSOCT, CASIA SS-1000, Tomey Corporation, Nagoya, Japan). Methods One randomly selected eye of 60 subjects was imaged under dark room conditions. The SSOCT 3-dimensional angle scan simultaneously obtains 128 radial scans of the anterior chamber for the entire circumference of the angle. Post-imaging analysis estimated the ITC index using in-built software. For intra-observer agreement for image grading, one examiner performed the grading twice in a masked fashion and random order after a 1-week interval. A second examiner graded images to assess inter-observer agreement for image grading. For intra-observer agreement for image acquisition, a single operator imaged patients twice. For inter-observer agreement for image acquisition, a single observer graded two sets of images acquired by two different operators on the same patient. Bland–Altman plots and 95 % limits of agreement (LOA) were reported. Results Study subjects were predominantly Chinese (54/60, 90 %) and female (42/60, 70 %), with a mean age of 65.5 years. The median ITC index for eyes with open angles (31/60) and closed angles was 20 % (95 % confidence interval [CI] — 13.6, 27.8) and 49 % (95%CI — 35.5, 69.2) respectively. The mean difference (95 % LOA) for intra-observer agreement for image grading and image acquisition were −0.8 % (−8.2, 6.5) and 0.6 % (−10.9, 9.7); corresponding inter- observer agreement were 0.1 % (−10, 10.1) and −0.3 % (−11.1, 10.5) respectively. Conclusions The inter- and intra-observer agreement of the ITC index, as a measure of extent of angle closure using SSOCT, was good.