title: Effect of Angle of Incidence on Anterior Chamber Angle Metrics From Optical Coherence Tomography.
abstract: OBJECTIVE
  To evaluate the local variability of anterior chamber angle (ACA) metrics obtained by time domain (TD) and spectral domain (SD) optical coherence tomography (OCT).
  
  
  METHODS
  Anterior-segment OCT imaging was performed on 30 normal eyes using Visante TD-OCT and 40 normal eyes using Cirrus SD-OCT. For Visante OCT, a single 16-mm line scan of the inferior angle with 3 slightly different rotations of 265, 270, and 275 degrees was performed. For Cirrus OCT, a 5-line raster of the inferior angle was performed, centering the third scan line at the 6 o'clock position, with 0.25 mm between lines. ACA measurements were taken for angle-opening distance (AOD) and trabecular iris space area (TISA) at 500/750 μm from the scleral spur for Visante OCT and at Schwalbe's line (SL) for Cirrus OCT.
  
  
  RESULTS
  For Visante OCT, AOD500 was 0.406 mm (SD=0.143 mm) and TISA500 was 0.139 mm (0.054 mm). There was no difference in AOD500, AOD750, TISA500, or TISA750 between the 3 scan orientations (P>0.1 for all comparisons). For Cirrus OCT, AOD500 was 0.850±0.318 mm and TISA500 was 0.325±0.145 mm. No difference was found in SL-AOD and SL-TISA between the 3 scan positions.
  
  
  CONCLUSIONS
  These findings suggest that small local changes in the position of the OCT line scan spaced up to 1.0 mm apart on Cirrus, or 10-degree apart on Visante, did not significantly alter the inferior ACA metrics in achieving reliable measurements in young healthy eyes. Given the absence of tracking and registration for current anterior-segment OCT instruments, this observation is of relevance for longitudinal and dynamic studies of angle geometry.
authors.affiliation: *Doheny Image Reading Center, Doheny Eye Institute ‡Department of Ophthalmology, David Geffen School of Medicine, Doheny Eye Institute, University of California, Los Angeles, Los Angeles, CA †The Affiliated Hospital of Medical College, Qingdao University Qingdao, Shandong, China.
authors.forename: Xiaojing
authors.initials: X
authors.lastname: Pan
authors.forename: Jyotsna
authors.initials: J
authors.lastname: Maram
authors.forename: Ken
authors.initials: K
authors.lastname: Marion
authors.forename: Anna
authors.initials: A
authors.lastname: Dastiridou
authors.forename: Zhou Yuan
authors.initials: ZY
authors.lastname: Zhang
authors.forename: Maria F
authors.initials: MF
authors.lastname: Dominguez-Velasco
authors.forename: Srinivas R
authors.initials: SR
authors.lastname: Sadda
authors.forename: Vikas
authors.initials: V
authors.lastname: Chopra
mesh_terms: D000328:Adult; D000867:Anterior Chamber / Q000033:anatomy & histology*; D001699:Biometry; D003941:Diagnostic Techniques, Ophthalmological; D005260:Female; D064368:Healthy Volunteers; D006801:Humans; D015994:Incidence; D007429:Intraocular Pressure; D007498:Iris / Q000033:anatomy & histology*; D016850:Limbus Corneae; D008297:Male; D008875:Middle Aged; D015203:Reproducibility of Results; D041623:Tomography, Optical Coherence / Q000295:instrumentation* / Q000379:methods; D014129:Trabecular Meshwork / Q000033:anatomy & histology*; D055815:Young Adult