title: Optimizing the information yield of 3-D OCT in glaucoma.
abstract: OBJECTIVE
  To determine, first, which regions of 3-D optical coherence tomography (OCT) volumes can be segmented completely in the majority of subjects and, second, the relationship between analyzed area and thickness measurement test-retest variability.
  
  
  METHODS
  Three-dimensional OCT volumes (6 × 6 mm) centered around the fovea and optic nerve head (ONH) of 925 Rotterdam Study participants were analyzed; 44 participants were scanned twice. Volumes were segmented into 10 layers, and we determined the area where all layers could be identified in at least 95% (macula) or 90% (ONH) of subjects. Macular volumes were divided in 2 × 2, 4 × 4, 6 × 6, 8 × 8, or 68 blocks. We placed two circles around the ONH; the ONH had to fit into the smaller circle, and the larger circle had to fit into the segmentable part of the volume. The area between the circles was divided in 3 to 12 segments. We determined the test-retest variability (coefficient of repeatability) of the retinal nerve fiber layer (RNFL) and ganglion cell layer (RGCL) thickness measurements as a function of size of blocks/segments.
  
  
  RESULTS
  Eighty-two percent of the macular volume could be segmented in at least 95% of subjects; for the ONH, this was 65% in at least 90%. The radii of the circles were 1.03 and 1.84 mm. Depending on the analyzed area, median test-retest variability ranged from 8% to 15% for macular RNFL, 11% to 22% for macular RGCL, 5% to 11% for the two together, and 18% to 22% for ONH RNFL.
  
  
  CONCLUSIONS
  Test-retest variability hampers a detailed analysis of 3-D OCT data. Combined macular RNFL and RGCL thickness averaged over larger areas had the best test-retest variability.
authors.affiliation: Department of Ophthalmology, Erasmus Medical Center, Rotterdam, The Netherlands.
authors.forename: Henriët
authors.initials: H
authors.lastname: Springelkamp
authors.forename: Kyungmoo
authors.initials: K
authors.lastname: Lee
authors.forename: Wishal D
authors.initials: WD
authors.lastname: Ramdas
authors.forename: Johannes R
authors.initials: JR
authors.lastname: Vingerling
authors.forename: Albert
authors.initials: A
authors.lastname: Hofman
authors.forename: Caroline C W
authors.initials: CC
authors.lastname: Klaver
authors.forename: Milan
authors.initials: M
authors.lastname: Sonka
authors.forename: Michael D
authors.initials: MD
authors.lastname: Abràmoff
authors.forename: Nomdo M
authors.initials: NM
authors.lastname: Jansonius
mesh_terms: D000465:Algorithms; D001369:Axons / Q000473:pathology*; D005260:Female; D005584:Fovea Centralis / Q000473:pathology; D005902:Glaucoma, Open-Angle / Q000175:diagnosis*; D006801:Humans; D021621:Imaging, Three-Dimensional; D007429:Intraocular Pressure; D008297:Male; D008875:Middle Aged; D009898:Optic Disk / Q000473:pathology; D015203:Reproducibility of Results; D012165:Retinal Ganglion Cells / Q000473:pathology*; D041623:Tomography, Optical Coherence