title: Novel anterior-chamber angle measurements by high-definition optical coherence tomography using the Schwalbe line as the landmark.
abstract: OBJECTIVE
  To propose the Schwalbe line (SL) as a new anatomical landmark, independent of the scleral spur (SS) location, for assessing anterior chamber angle (ACA) width quantitatively with high-definition optical coherence tomography (HD-OCT).
  
  
  METHODS
  Study subjects underwent dark-room gonioscopy and HD-OCT in one randomly selected eye. The authors developed a computer-aided program to define two new quantitative parameters for assessing ACA width: Schwalbe line-angle opening distance (SL-AOD) measured at the SL, and Schwalbe line-trabecular-iris space area (SL-TISA) measured 500 μm from the SL. The associations between SL parameters, SS parameters and gonioscopic grading were evaluated.
  
  
  RESULTS
  Seventy-three (47 females, 26 males) subjects were recruited, the majority of whom were Chinese (89%). The authors excluded 29 images (19.9%) owing to poor image quality, leaving 117 HD-OCT images (65 nasal, 52 temporal) for analysis. SL and SS could be identified in 95% and 85% of quadrants respectively (p = 0.035). SL-AOD and SL-TISA were significantly correlated with SS parameters (all r ≥ 0.85) and gonioscopic grading (all r ≥ 0.69). In eyes with closed angles (n = 36), SL parameters showed strong correlations with gonioscopic grading (r ranged from 0.43 to 0.44). Conclusions Novel angle parameters, based on SL as a landmark, may be useful to quantify ACA width and to assess for risk of angle closure.
authors.affiliation: Singapore Eye Research, Institute and Singapore National Eye Centre, Singapore.
authors.forename: Carol Y
authors.initials: CY
authors.lastname: Cheung
authors.forename: Ce
authors.initials: C
authors.lastname: Zheng
authors.forename: Ching-Lin
authors.initials: CL
authors.lastname: Ho
authors.forename: Tin A
authors.initials: TA
authors.lastname: Tun
authors.forename: Rajesh S
authors.initials: RS
authors.lastname: Kumar
authors.forename: Fouad El
authors.initials: FE
authors.lastname: Sayyad
authors.forename: Tien Y
authors.initials: TY
authors.lastname: Wong
authors.forename: Tin
authors.initials: T
authors.lastname: Aung
mesh_terms: D000867:Anterior Chamber / Q000033:anatomy & histology*; D044466:Asian People; D005260:Female; D015812:Glaucoma, Angle-Closure / Q000209:etiology; D006068:Gonioscopy / Q000379:methods*; D006801:Humans; D008297:Male; D011446:Prospective Studies; D012984:Software; D041623:Tomography, Optical Coherence / Q000379:methods*