title: Directional Optical Coherence Tomography Reveals Reliable Outer Nuclear Layer Measurements.
abstract: Directional Optical Coherence Tomography (D-OCT) is a method used to optically segment and identify the outer nuclear layer (ONL) in vivo. The purpose of this study was to determine the repeatability and reproducibility of D-OCT ONL thickness measurements in healthy eyes.
  
  
  
  Sixteen healthy eyes of sixteen subjects were imaged using the Cirrus SD-OCT. The OCT beam entry position was varied horizontally and vertically through the pupil, and cross-sectional images were obtained at baseline and 1-month follow-up by two observers. Detailed segmentation was performed to quantify the thickness of ONL without the inclusion of overlying Henle Fiber Layer. Inter-observer, intra-observer, and inter-visit variability was evaluated using Bland-Altman and coefficient of variation analysis for each category.
  
  
  
  All 16 eyes were successfully imaged, registered, and segmented. The maximum mean (SD) inter-operator difference was 2.6 (4.8) μm. The maximum mean (SD) intra-operator difference was 2.4 (5.3) μm. There was no statistically significant difference in ONL measurements detected between baseline and follow-up (p > 0.05). The mean (SD) differences measured across visits by one operator varied from -1.6 (3.1) to 1.1 (6.1) μm. The mean (SD) coefficient of variance (CV%) for all sectors with horizontal orientation was 9.1% (2.3%), 10.1% (2.5%), and 8.6% (2.3%) for inter-observer, intra-observer, and inter-visit, respectively. The mean (SD) coefficient of variance (CV%) for all sectors with vertical orientation was 8.3% (1.8%), 6.9% (1.4%), and 8.3% (2.1%) for inter-observer, intra-observer, and inter-visit, respectively. The majority of the variation of paired repeated measurements originated from between-subject variance. The within-subject variance accounted for less than 1% of the total variability.
  
  
  
  ONL thickness measurements can be quantified with good repeatability and reproducibility using D-OCT. Identifying the magnitude of D-OCT variability among normal subjects will allow for improved development of future clinical studies that quantitatively track the progression of macular pathology.
authors.affiliation: *OD †MD ‡PhD §OD, FAAO School of Optometry (KKT, MCL), Vision Science Program (BJL, MCL), University of California, Berkeley, Berkeley; West Coast Retina Medical Group (BJL), San Francisco; and Clinical Research Center (YZ, MCL), University of California, Berkeley, Berkeley, California.
authors.forename: Kevin K
authors.initials: KK
authors.lastname: Tong
authors.forename: Brandon J
authors.initials: BJ
authors.lastname: Lujan
authors.forename: Yixiu
authors.initials: Y
authors.lastname: Zhou
authors.forename: Meng C
authors.initials: MC
authors.lastname: Lin
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D003430:Cross-Sectional Studies; D005260:Female; D064368:Healthy Volunteers; D006801:Humans; D008297:Male; D008875:Middle Aged; D009412:Nerve Fibers; D015588:Observer Variation; D015203:Reproducibility of Results; D055351:Retinal Neurons / Q000166:cytology*; D041623:Tomography, Optical Coherence / Q000379:methods*