title: Overestimation of subfoveal choroidal thickness by measurement based on horizontally compressed optical coherence tomography images.
abstract: OBJECTIVE
  To measure the difference in subfoveal choroidal thickness between 1:1 pixel (horizontally compressed) images and 1:1 micron images in age-related macular degeneration.
  
  
  METHODS
  This study included 122 eyes from 122 patients diagnosed with age-related macular degeneration. Choroidal thickness was measured using enhanced-depth imaging optical coherence tomography. The measurement line was drawn as a perpendicular line between Bruch's membrane and the chorio-scleral interface. The thickness was compared between measurements based on a 1:1 pixel image and a 1:1 micron image. Eyes with a straight vertical measurement line and oblique measurement line were classified into vertical measurement group and oblique measurement group, respectively. Intra-group comparisons of subfoveal choroidal thickness measurements based on the 1:1 pixel images and the 1:1 micron images were performed for the two groups.
  
  
  RESULTS
  The mean subfoveal choroidal thicknesses measured on the 1:1 pixel images and the 1:1 micron images were 232.3 ± 106.4 μm and 228.9 ± 108.1 μm, respectively (p = 0.003). In the vertical measurement group (86 eyes), the mean subfoveal choroidal thickness was 226.3 ± 109.9 μm and 225.4 ± 112.0 μm, respectively (p = 0.423). In the oblique measurement group (36 eyes), the thickness was 246.5 ± 97.3 μm and 237.5 ± 98.9 μm, respectively (p < 0.001).
  
  
  CONCLUSIONS
  Significant overestimation of the subfoveal choroidal thickness was noted when it was measured on a 1:1 pixel image. This finding suggests that the measurement of choroidal thickness should be performed based on a 1:1 micron image, especially if the measurement line is not vertical.
authors.affiliation: Department of Ophthalmology, Samsung Medical Center, Sungkyunkwan University School of Medicine, #50 Irwon-dong, Kangnam-gu, Seoul 135-710, Korea.
authors.forename: Jae Hui
authors.initials: JH
authors.lastname: Kim
authors.forename: Se Woong
authors.initials: SW
authors.lastname: Kang
authors.forename: Hyo Shin
authors.initials: HS
authors.lastname: Ha
authors.forename: Sang Jin
authors.initials: SJ
authors.lastname: Kim
authors.forename: Jae Ryung
authors.initials: JR
authors.lastname: Kim
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D020533:Angiogenesis Inhibitors / Q000627:therapeutic use; D002829:Choroid / Q000473:pathology*; D015862:Choroid Diseases / Q000175:diagnosis* / Q000188:drug therapy; D044962:Data Compression; D005584:Fovea Centralis; D006801:Humans; D007091:Image Processing, Computer-Assisted; D058449:Intravitreal Injections; D008875:Middle Aged; D009929:Organ Size; D010778:Photochemotherapy; D011127:Polyps / Q000175:diagnosis* / Q000188:drug therapy; D041623:Tomography, Optical Coherence; D042461:Vascular Endothelial Growth Factor A / Q000037:antagonists & inhibitors; D057135:Wet Macular Degeneration / Q000175:diagnosis* / Q000188:drug therapy
chemical_list: D020533:Angiogenesis Inhibitors; C467484:VEGFA protein, human; D042461:Vascular Endothelial Growth Factor A