title: Adjustment of the retinal angle in SD-OCT of glaucomatous eyes provides better intervisit reproducibility of peripapillary RNFL thickness.
abstract: OBJECTIVE
  To report an automated method for adjustment of the retinal angle in spectral-domain optical coherence tomography (SD-OCT) and compare its intervisit reproducibility of the peripapillary retinal nerve fiber layer (RNFL) thicknesses of glaucomatous eyes to that obtained by the Cirrus algorithm.
  
  
  METHODS
  Fifty-six glaucoma and glaucoma suspect subjects were repeatedly imaged, and optic nerve head (ONH)-centered OCT image volumes (200×200×1024 voxels, 6×6×2 mm3, Cirrus HD-OCT machine) were acquired within a 4-month period from one eye of the 56 patients. Retinal angle correction in B-scans was accomplished by adjusting the angle using the voxel aspect ratio of the SD-OCT followed by straightening of rotated A-scans. The RNFL layer was automatically segmented using the Iowa Reference Algorithm. Reproducibility of the peripapillary RNFL thicknesses was determined by intraclass correlation coefficient (ICC), coefficient of variation (CV), repeatability coefficient (RC), and 95% tolerance limit (TL) for the Iowa Reference Algorithm without and with the retinal angle correction and for the Cirrus algorithm (Cirrus version 5.1.0.96).
  
  
  RESULTS
  The angle corrected Iowa Reference Algorithm (ICC: 0.990, 95% confidence interval [CI]: 0.983-0.994) for peripapillary RNFL thicknesses showed significantly better reproducibility than the nonangle corrected algorithm (ICC: 0.964, 95% CI: 0.940-0.979) and the Cirrus algorithm (ICC: 0.960, 95% CI: 0.933-0.976) based on the 95% CIs for the ICCs.
  
  
  CONCLUSIONS
  Angle correction leads to more consistent peripapillary RNFL thicknesses. This may lead to improved management of patients with glaucoma.
authors.affiliation: Department of Electrical and Computer Engineering, University of Iowa, Iowa City, Iowa 52242, USA.
authors.forename: Kyungmoo
authors.initials: K
authors.lastname: Lee
authors.forename: Milan
authors.initials: M
authors.lastname: Sonka
authors.forename: Young H
authors.initials: YH
authors.lastname: Kwon
authors.forename: Mona K
authors.initials: MK
authors.lastname: Garvin
authors.forename: Michael D
authors.initials: MD
authors.lastname: Abràmoff
mesh_terms: D000368:Aged; D000704:Analysis of Variance; D005260:Female; D005901:Glaucoma / Q000175:diagnosis*; D006801:Humans; D008297:Male; D008875:Middle Aged; D009412:Nerve Fibers / Q000473:pathology*; D009900:Optic Nerve / Q000473:pathology*; D015203:Reproducibility of Results; D041623:Tomography, Optical Coherence / Q000379:methods*
keywords: peripapillary retinal nerve fiber layer (RNFL) thickness; retinal angle adjustment; spectral-domain coherence tomography (SD-OCT)