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

Graefes Arch Clin Exp Ophthalmol. 2013 Apr;251(4):1205-11. doi: 10.1007/s00417-012-2158-6. Epub 2012 Sep 23.


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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Aged
  • Area Under Curve
  • Female
  • Fourier Analysis
  • Glaucoma, Angle-Closure / classification
  • Glaucoma, Angle-Closure / diagnosis*
  • Gonioscopy
  • Humans
  • Imaging, Three-Dimensional
  • Iris / pathology*
  • Male
  • Middle Aged
  • Observer Variation
  • Prospective Studies
  • ROC Curve
  • Tomography, Optical Coherence*
  • Trabecular Meshwork / pathology*