title: Assessment of circumferential angle-closure by the iris-trabecular contact index with swept-source optical coherence tomography.
abstract: OBJECTIVE
  To evaluate the diagnostic performance 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) in comparison with gonioscopy.
  
  
  METHODS
  Prospective observational study.
  
  
  METHODS
  A total of 108 normal subjects and 32 subjects with angle-closure.
  
  
  METHODS
  The SSOCT 3-dimensional angle scans, which obtain radial scans for the entire circumference of the angle, were performed under dark conditions and analyzed using customized software by a single examiner masked to the subjects' clinical details. The ITC index was calculated as a percentage of the angle that was closed on SSOCT images. First-order agreement coefficient (AC1) statistics and area under the receiver operating characteristic curve (AUC) analyses were performed for angle-closure on the basis of the ITC index in comparison with gonioscopy.
  
  
  METHODS
  Angle-closure on gonioscopy was defined as nonvisibility of posterior trabecular meshwork for at least 2 quadrants. Agreement of the ITC index with gonioscopically defined angle-closure was assessed using the AC1 statistic.
  
  
  RESULTS
  Study subjects were predominantly Chinese (95.7%) and female (70.7%), with a mean age of 59.2 (standard deviation, 8.9) years. The median ITC index was 15.24% for gonioscopically open-angle eyes (n = 108) and 48.5% for closed-angle eyes (n = 32) (P = 0.0001). The agreement for angle-closure based on ITC index cutoffs (>35% and ≥50%) and gonioscopic angle-closure was 0.699 and 0.718, respectively. The AUC for angle-closure detection using the ITC index was 0.83 (95% confidence interval, 0.76-0.89), with an ITC index >35% having a sensitivity of 71.9% and specificity of 84.3%.
  
  
  CONCLUSIONS
  The ITC index is a summary measure of the circumferential extent of angle-closure as imaged with SSOCT. The index had moderate agreement and good diagnostic performance for angle-closure with gonioscopy as the reference standard.
authors.affiliation: Singapore National Eye Centre, Singapore and Singapore Eye Research Institute, Singapore; Yong Loo Lin School of Medicine, National University of Singapore, Singapore.
authors.forename: Mani
authors.initials: M
authors.lastname: Baskaran
authors.forename: Sue-Wei
authors.initials: SW
authors.lastname: Ho
authors.forename: Tin A
authors.initials: TA
authors.lastname: Tun
authors.forename: Alicia C
authors.initials: AC
authors.lastname: How
authors.forename: Shamira A
authors.initials: SA
authors.lastname: Perera
authors.forename: David S
authors.initials: DS
authors.lastname: Friedman
authors.forename: Tin
authors.initials: T
authors.lastname: Aung
mesh_terms: D000867:Anterior Chamber / Q000473:pathology; D019540:Area Under Curve; D005260:Female; D015812:Glaucoma, Angle-Closure / Q000175:diagnosis*; D006068:Gonioscopy; D006801:Humans; D021621:Imaging, Three-Dimensional; D007429:Intraocular Pressure; D007498:Iris / Q000473:pathology*; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies; D000267:Tissue Adhesions; D041623:Tomography, Optical Coherence / Q000379:methods*; D014065:Tonometry, Ocular; D014129:Trabecular Meshwork / Q000473:pathology*