title: Determination of axial length requiring adjustment of measured circumpapillary retinal nerve fiber layer thickness for ocular magnification.
abstract: OBJECTIVE
  To determine the axial length requiring adjustment of measured circumpapillary retinal nerve fiber layer (cpRNFL) thickness to account for ocular magnification during spectral-domain optical coherence tomography (SD-OCT).
  
  
  METHODS
  In this prospective study, 148 eyes of 148 healthy student volunteers were imaged by two examiners using three-dimensional SD-OCT. In 54 randomly selected eyes, total cpRNFL thickness was measured with and without adjustment for ocular magnification to establish intra-examiner and inter-examiner measurement error. The 148 eyes were then divided into three groups according to the error values: control group (difference in the corrected and uncorrected total cpRNFL thickness was within the measurement error range), thinner group (the corrected total cpRNFL thickness was less than the uncorrected one), and thicker group (the corrected total cpRNFL thickness was more than the uncorrected one). The cutoff values of axial length between the control and the other groups were calculated by receiver operating characteristic analysis.
  
  
  RESULTS
  Measurement error ranged from 4.2 to 5.3 µm; the threshold value was defined as 5.3 µm. The cutoff values of axial length between the thinner and the control groups and between the control and the thicker groups were 23.60 (area under the curve [AUC] = 0.959) and 25.55 (AUC = 0.944) mm, respectively.
  
  
  CONCLUSIONS
  Axial lengths shorter than 23.60 mm and longer than 25.55 mm require adjustment of measured cpRNFL thickness to account for ocular magnification during SD-OCT.
  
  
  BACKGROUND
  UMIN Clinical Trials Registry (http://www.umin.ac.jp/) under unique trial number UMIN000013248 (date of registration: 02/24/2014).
authors.affiliation: Orthoptics and Visual Science, Department of Rehabilitation, School of Allied Health Sciences, Kitasato University, Kanagawa, Japan.
authors.forename: Kazunori
authors.initials: K
authors.lastname: Hirasawa
authors.affiliation: Orthoptics and Visual Science, Department of Rehabilitation, School of Allied Health Sciences, Kitasato University, Kanagawa, Japan.
authors.forename: Nobuyuki
authors.initials: N
authors.lastname: Shoji
authors.affiliation: Orthoptics and Visual Science, Department of Rehabilitation, School of Allied Health Sciences, Kitasato University, Kanagawa, Japan.
authors.forename: Yukako
authors.initials: Y
authors.lastname: Yoshii
authors.affiliation: Orthoptics and Visual Science, Department of Rehabilitation, School of Allied Health Sciences, Kitasato University, Kanagawa, Japan.
authors.forename: Shota
authors.initials: S
authors.lastname: Haraguchi
mesh_terms: D000328:Adult; D003315:Cornea / Q000473:pathology; D005123:Eye / Q000473:pathology; D005901:Glaucoma / Q000473:pathology*; D064368:Healthy Volunteers; D006801:Humans; D009216:Myopia / Q000473:pathology; D009412:Nerve Fibers / Q000473:pathology*; D009900:Optic Nerve / Q000473:pathology*; D012160:Retina / Q000473:pathology*; D041623:Tomography, Optical Coherence