title: Optimal number of angle images for calculating anterior angle volume and iris volume measurements.
abstract: OBJECTIVE
  We determined the optimal number of angle images required to obtain reliable measurements of trabecular-iris circumferential volume (TICV) and iris volume (IV) using swept-source Fourier domain anterior segment optical coherence tomography (SSFD-ASOCT) scans in narrow angle eyes.
  
  
  METHODS
  Scleral spur landmarks (SSL) were manually identified on ASOCT angle images from 128 meridians from each of 24 eyes with chronic primary angle closure (PAC) spectrum of disease. The anterior and posterior corneal curves, and the anterior and posterior iris surfaces were identified automatically by the anterior chamber analysis and interpretation (ACAI) software, then manually examined and edited by the reader if required. Trabecular-iris circumferential volume at 750 μm from SSL (TICV750) and IV were subsequently calculated using varying numbers of angle images. Threshold error was determined to be less than the lower 95% confidence limit of mean absolute percent error (MAPE) of the change in TICV or IV resulting from laser peripheral iridotomy, which would be 17% for TICV and 5% for IV, based on previous studies. The optimal number of angle images was the smallest number of images where MAPE was less than this threshold for TICV and IV.
  
  
  RESULTS
  A total of 32 equally-spaced angle images (16 meridians) was required to estimate TICV750 and 16 angle images (8 meridians) to estimate IV. Both were within 4.6% and 1.6% of MAPE, respectively.
  
  
  CONCLUSIONS
  It is possible to determine TICV and IV parameters reliably in narrow angles without evaluating all 128 meridians obtained with SSFD-ASOCT.
authors.affiliation: Ruiz Department of Ophthalmology and Visual Science, The University of Texas Medical School at Houston, Houston, Texas, United States 2Robert Cizik Eye Clinic, Houston, Texas, United States.
authors.forename: Lauren S
authors.initials: LS
authors.lastname: Blieden
authors.affiliation: Ruiz Department of Ophthalmology and Visual Science, The University of Texas Medical School at Houston, Houston, Texas, United States.
authors.forename: Alice Z
authors.initials: AZ
authors.lastname: Chuang
authors.affiliation: Robert Cizik Eye Clinic, Houston, Texas, United States.
authors.forename: Laura A
authors.initials: LA
authors.lastname: Baker
authors.affiliation: Ruiz Department of Ophthalmology and Visual Science, The University of Texas Medical School at Houston, Houston, Texas, United States 2Robert Cizik Eye Clinic, Houston, Texas, United States.
authors.forename: Nicholas P
authors.initials: NP
authors.lastname: Bell
authors.affiliation: Ruiz Department of Ophthalmology and Visual Science, The University of Texas Medical School at Houston, Houston, Texas, United States 2Robert Cizik Eye Clinic, Houston, Texas, United States.
authors.forename: Timothy S
authors.initials: TS
authors.lastname: Fuller
authors.affiliation: Ruiz Department of Ophthalmology and Visual Science, The University of Texas Medical School at Houston, Houston, Texas, United States.
authors.forename: Kimberly A
authors.initials: KA
authors.lastname: Mankiewicz
authors.affiliation: Ruiz Department of Ophthalmology and Visual Science, The University of Texas Medical School at Houston, Houston, Texas, United States 2Robert Cizik Eye Clinic, Houston, Texas, United States.
authors.forename: Robert M
authors.initials: RM
authors.lastname: Feldman
mesh_terms: D000368:Aged; D000869:Anterior Eye Segment / Q000473:pathology*; D005260:Female; D015812:Glaucoma, Angle-Closure / Q000175:diagnosis* / Q000473:pathology; D006801:Humans; D007498:Iris / Q000473:pathology*; D008297:Male; D008875:Middle Aged; D015203:Reproducibility of Results; D012189:Retrospective Studies; D041623:Tomography, Optical Coherence / Q000379:methods*; D014129:Trabecular Meshwork / Q000473:pathology
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