title: Effect of signal strength on reproducibility of circumpapillary retinal nerve fiber layer thickness measurement and its classification by spectral-domain optical coherence tomography.
abstract: OBJECTIVE
  To assess the effect of signal strength (SS) on the reproducibility of circumpapillary retinal nerve fiber layer (cpRNFL) thickness measurement (measurement agreement) and its color-coded classification (classification agreement) by Cirrus spectral-domain optical coherence tomography (OCT).
  
  
  METHODS
  Seven hundred and eighty-nine participants, consecutively enrolled from December 2009 to August 2010, underwent two repeated Cirrus OCT scans to measure cpRNFL thickness (optic disc cube 200 × 200). Intraclass correlation (ICC) and linear-weighted kappa coefficient (κ) were calculated as indicators for cpRNFL measurement and classification agreement. The difference in cpRNFL thickness measurements between repeated OCT scans (inter-scan measurement difference) was correlated with mean SS, SS change or difference between repeated OCT scans (inter-scan SS difference), and average cpRNFL thickness.
  
  
  RESULTS
  Mean SS was negatively correlated with inter-scan SS difference and was positively correlated with the inter-scan measurement difference. Repeated scans with SS change (inter-scan SS difference = 1 or 2) showed larger variability than scans without SS change (inter-scan SS difference = 0) in total average cpRNFL and all quadrant maps except for the nasal quadrant. Multivariate analysis revealed that inter-scan measurement differences increased in subjects with thinner cpRNFL thicknesses and in scans with lower mean SS and higher inter-scan SS differences. Measurement agreement (ICC) in groups with larger inter-scan SS differences (=2) was lower than those with smaller inter-scan SS differences (=0 or 1) in their average cpRNFL and inferior quadrant maps. Classification agreement (κ) in groups with larger inter-scan SS differences (=2) was lower than those with smaller inter-scan SS differences (=0 or 1) in their average cpRNFL and quadrant maps (superior and inferior quadrant) although statistically not significant.
  
  
  CONCLUSIONS
  Special attention should be paid when comparing the cpRNFL thickness measurement and color-coded classification of 2 or more Cirrus OCT scans as the agreements may be susceptible to SS differences.
authors.affiliation: Department of Ophthalmology, Institute of Vision Research, Yonsei University College of Medicine, CPO Box 8044, Seoul, 120-752, Korea.
authors.forename: Ji Hyun
authors.initials: JH
authors.lastname: Kim
authors.affiliation: Department of Ophthalmology, Institute of Vision Research, Yonsei University College of Medicine, CPO Box 8044, Seoul, 120-752, Korea.
authors.forename: Na Rae
authors.initials: NR
authors.lastname: Kim
authors.affiliation: Department of Applied Statistics, Yonsei University, Seoul, Korea.
authors.forename: Hyunjoong
authors.initials: H
authors.lastname: Kim
authors.affiliation: Department of Ophthalmology, Institute of Vision Research, Yonsei University College of Medicine, CPO Box 8044, Seoul, 120-752, Korea. eslee.korea@gmail.com.
authors.forename: Eun Suk
authors.initials: ES
authors.lastname: Lee
authors.affiliation: Department of Ophthalmology, Institute of Vision Research, Yonsei University College of Medicine, CPO Box 8044, Seoul, 120-752, Korea.
authors.forename: Gong Je
authors.initials: GJ
authors.lastname: Seong
authors.affiliation: Department of Ophthalmology, Institute of Vision Research, Yonsei University College of Medicine, CPO Box 8044, Seoul, 120-752, Korea.
authors.forename: Chan Yun
authors.initials: CY
authors.lastname: Kim
mesh_terms: D005260:Female; D005901:Glaucoma / Q000145:classification* / Q000175:diagnosis; D006801:Humans; D007429:Intraocular Pressure / Q000502:physiology; D008297:Male; D008875:Middle Aged; D009412:Nerve Fibers / Q000473:pathology*; D009798:Ocular Hypertension / Q000145:classification / Q000175:diagnosis; D009898:Optic Disk / Q000473:pathology*; D009901:Optic Nerve Diseases / Q000145:classification* / Q000175:diagnosis; D015203:Reproducibility of Results; D012165:Retinal Ganglion Cells / Q000473:pathology*; D041623:Tomography, Optical Coherence; D014065:Tonometry, Ocular; D014792:Visual Acuity / Q000502:physiology; D058609:Visual Field Tests; D014794:Visual Fields