title: Swept source optical coherence tomography measurement of the iris-trabecular contact (ITC) index: a new parameter for angle closure.
abstract: OBJECTIVE
  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.
authors.affiliation: Singapore Eye Research Institute and Singapore National Eye Centre, Singapore, Singapore.
authors.forename: Sue-Wei
authors.initials: SW
authors.lastname: Ho
authors.forename: Mani
authors.initials: M
authors.lastname: Baskaran
authors.forename: Ce
authors.initials: C
authors.lastname: Zheng
authors.forename: Tin A
authors.initials: TA
authors.lastname: Tun
authors.forename: Shamira A
authors.initials: SA
authors.lastname: Perera
authors.forename: Arun K
authors.initials: AK
authors.lastname: Narayanaswamy
authors.forename: David S
authors.initials: DS
authors.lastname: Friedman
authors.forename: Tin
authors.initials: T
authors.lastname: Aung
mesh_terms: D000368:Aged; D019540:Area Under Curve; D005260:Female; D005583:Fourier Analysis; D015812:Glaucoma, Angle-Closure / Q000145:classification / Q000175:diagnosis*; D006068:Gonioscopy; D006801:Humans; D021621:Imaging, Three-Dimensional; D007498:Iris / Q000473:pathology*; D008297:Male; D008875:Middle Aged; D015588:Observer Variation; D011446:Prospective Studies; D012372:ROC Curve; D041623:Tomography, Optical Coherence; D014129:Trabecular Meshwork / Q000473:pathology*