title: Effect of optical coherence tomography scan decentration on macular center subfield thickness measurements.
abstract: OBJECTIVE
  To investigate the effect of optical coherence tomography macular grid displacement on retinal thickness measurements.
  
  
  METHODS
  SD-OCT macular scans of 66 eyes with various retinal thicknesses were selected. Decentration of the 1-, 3-, 6-mm-diameter macular grid was simulated by manually adjusting the distance between center of the fovea (cFovea) and center of the grid (cGrid). Center subfield thickness (CSF) between the internal limiting membrane and the top of the retinal pigment epithelium was measured along the displacement distance where the grid was displaced in eight cardinal directions from the cFovea in steps of 100 μm within the central 1-mm subfield and then by 200 μm within the inner subfields. One-way/mixed-effects repeated-measures ANOVA models were used to determine changes of CSF (ΔCSF) as a function of displacement distance (for α = 0.05, power = 0.80 and effect size = 0.1). The interactions between the displacement distance and direction, center point thickness (CPT), and foveal contour were also analyzed.
  
  
  RESULTS
  The CSF measurement showed statistically significant error when the displacement distance between cFovea and cGrid exceeded 200 μm. The direction of displacement did not affect the ΔCSF-distance relationship, while the CPT and foveal contour significantly affected the relationship, in that some subgroups showed slightly larger tolerance in the displacement distance up to 300 μm before reaching significant ΔCSF.
  
  
  CONCLUSIONS
  Small displacement distances of the macular grid from the cFovea affect CSF measurements throughout a broad range of thicknesses and retinal contour alterations from disease. Accurate registration of OCT scans or post hoc repositioning of the grid is essential to optimize CSF accuracy.
authors.affiliation: Fundus Photograph Reading Center, Department of Ophthalmology and Visual Sciences, University of Wisconsin-Madison, Madison, Wisconsin, USA.
authors.forename: Jeong W
authors.initials: JW
authors.lastname: Pak
authors.forename: Ashwini
authors.initials: A
authors.lastname: Narkar
authors.forename: Sapna
authors.initials: S
authors.lastname: Gangaputra
authors.forename: Ronald
authors.initials: R
authors.lastname: Klein
authors.forename: Barbara
authors.initials: B
authors.lastname: Klein
authors.forename: Stacy
authors.initials: S
authors.lastname: Meuer
authors.forename: Yijun
authors.initials: Y
authors.lastname: Huang
authors.forename: Ronald P
authors.initials: RP
authors.lastname: Danis
mesh_terms: D000704:Analysis of Variance; D006801:Humans; D008266:Macula Lutea / Q000033:anatomy & histology*; D015233:Models, Statistical; D012189:Retrospective Studies; D041623:Tomography, Optical Coherence / Q000379:methods*
keywords: OCT artifacts; SD OCT; decentration; retinal thickness