title: Characterisation of Schlemm's canal cross-sectional area.
abstract: OBJECTIVE
  To compare three methods of Schlemm's canal (SC) cross-sectional area (CSA) measurement.
  
  
  METHODS
  Ten eyes (10 healthy volunteers) were imaged three times using spectral-domain optical coherence tomography (Cirrus HD-OCT, Zeiss, Dublin, California, USA). Aqueous outflow vascular structures and SC collector channel ostia were used as landmarks to identify a reference location within the limbus. SC CSA was assessed within a 1 mm segment (±15 frames of the reference, 31 frames in all) by three techniques. (1) Using a random number table, SC CSA in five random frames from the set of 31 surrounding the reference were measured and averaged. (2) The most easily visualised SC location (subjective) was measured, and (3) SC CSA was measured in all 31 consecutive B-scans, and averaged. (comprehensive average, gold standard). Subjective and random CSAs were compared with the comprehensive by general estimating equation modelling, and structural equation modelling quantified agreement.
  
  
  RESULTS
  The average from five random locations (4175±1045 µm(2)) was not significantly different than that obtained from the gold standard comprehensive assessment (4064±1308 µm(2), p=0.6537). Subjectively located SC CSA (7614±2162 µm(2)) was significantly larger than the comprehensive gold standard SC CSA (p<0.0001). The average of five random frames produced significantly less bias than did subjective location, yielding a calibration line crossing the 'no-bias' line.
  
  
  CONCLUSIONS
  Subjectively located SC CSA measurements produce high estimates of SC CSA. SC assessed by measuring five random locations estimate CSA was similar to the gold standard estimate.
authors.affiliation: Department of Ophthalmology, UPMC Eye Center, Eye and Ear Institute, Ophthalmology and Visual Science Research Center, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, USA Department of Bioengineering, Swanson School of Engineering, University of Pittsburgh, Pittsburgh, Pennsylvania, USA.
authors.forename: Larry
authors.initials: L
authors.lastname: Kagemann
authors.affiliation: Department of Ophthalmology, UPMC Eye Center, Eye and Ear Institute, Ophthalmology and Visual Science Research Center, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, USA.
authors.forename: Jessica E
authors.initials: JE
authors.lastname: Nevins
authors.affiliation: Department of Ophthalmology, UPMC Eye Center, Eye and Ear Institute, Ophthalmology and Visual Science Research Center, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, USA Department of Bioengineering, Swanson School of Engineering, University of Pittsburgh, Pittsburgh, Pennsylvania, USA.
authors.forename: Ninj-Jiun
authors.initials: NJ
authors.lastname: Jan
authors.affiliation: Department of Ophthalmology, UPMC Eye Center, Eye and Ear Institute, Ophthalmology and Visual Science Research Center, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, USA.
authors.forename: Gadi
authors.initials: G
authors.lastname: Wollstein
authors.affiliation: Department of Ophthalmology, UPMC Eye Center, Eye and Ear Institute, Ophthalmology and Visual Science Research Center, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, USA Department of Bioengineering, Swanson School of Engineering, University of Pittsburgh, Pittsburgh, Pennsylvania, USA.
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Ishikawa
authors.affiliation: Zeiss Inc., Dublin, California, USA.
authors.forename: Janice
authors.initials: J
authors.lastname: Kagemann
authors.affiliation: Department of Ophthalmology, UPMC Eye Center, Eye and Ear Institute, Ophthalmology and Visual Science Research Center, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, USA Department of Bioengineering, Swanson School of Engineering, University of Pittsburgh, Pittsburgh, Pennsylvania, USA.
authors.forename: Ian A
authors.initials: IA
authors.lastname: Sigal
authors.affiliation: Department of Ophthalmology, UPMC Eye Center, Eye and Ear Institute, Ophthalmology and Visual Science Research Center, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, USA.
authors.forename: Zach
authors.initials: Z
authors.lastname: Nadler
authors.affiliation: Department of Ophthalmology, UPMC Eye Center, Eye and Ear Institute, Ophthalmology and Visual Science Research Center, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, USA.
authors.forename: Yun
authors.initials: Y
authors.lastname: Ling
authors.affiliation: Department of Ophthalmology, UPMC Eye Center, Eye and Ear Institute, Ophthalmology and Visual Science Research Center, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, USA Department of Bioengineering, Swanson School of Engineering, University of Pittsburgh, Pittsburgh, Pennsylvania, USA.
authors.forename: Joel S
authors.initials: JS
authors.lastname: Schuman
mesh_terms: D000328:Adult; D019412:Anatomy, Cross-Sectional; D001082:Aqueous Humor / Q000502:physiology; D003315:Cornea / Q000033:anatomy & histology*; D005260:Female; D064368:Healthy Volunteers; D006801:Humans; D016850:Limbus Corneae / Q000033:anatomy & histology*; D008297:Male; D008875:Middle Aged; D012590:Sclera / Q000033:anatomy & histology*; D041623:Tomography, Optical Coherence; D055815:Young Adult
keywords: Aqueous humour; Imaging