title: Assessment of choroidal thickness before and after steep Trendelenburg position using swept-source optical coherence tomography.
abstract: BACKGROUND
  To evaluate changes in choroidal thickness before and after steep Trendelenburg position (STP, 40° head-down) using automated segmentation software to analyse swept-source optical coherence tomography (SS-OCT) data.
  
  
  METHODS
  The eyes of 20 healthy volunteers underwent a three-dimensional wide scanning protocol with SS-OCT (Topcon, Tokyo, Japan) at baseline, immediately after STP was initiated, and 5, 10 and 15 min after STP; blood pressure and heart rate were measured concurrently. The predictive mean difference was calculated using a generalised linear mixed model that adjusted for potential confounders.
  
  
  RESULTS
  Mean choroidal thickness significantly and transiently increased immediately (268.18±9.24 μm, p<0.01) and 5 min (264.25±9.30 μm, p=0.03) after STP, relative to baseline (256.51±9.20 μm). However, choroidal thickness decreased by 10 min (262.51±9.34 μm, p=0.15) and 15 min (261.38±9.40 μm, p=0.37) after STP. Mean arterial pressure also transiently increased from baseline (78.2±1.2 mm Hg) immediately after STP (79.9±1.1 mm Hg, p=0.01), but normalised by 5 min after STP (p>0.05 for all comparisons ≥5 min).
  
  
  CONCLUSIONS
  Choroidal thickness significantly but transiently increases after adopting STP, as evaluated by automated layer segmentation analysis of SS-OCT data.
authors.affiliation: Department of Ophthalmology, Severance Hospital, Institute of Vision Research, Yonsei University College of Medicine, Seoul, Korea.
authors.forename: Tyler Hyungtaek
authors.initials: TH
authors.lastname: Rim
authors.affiliation: Department of Ophthalmology, Severance Hospital, Institute of Vision Research, Yonsei University College of Medicine, Seoul, Korea.
authors.forename: Christopher Seungkyu
authors.initials: CS
authors.lastname: Lee
authors.affiliation: Department of Ophthalmology, Severance Hospital, Institute of Vision Research, Yonsei University College of Medicine, Seoul, Korea.
authors.forename: Kangyoon
authors.initials: K
authors.lastname: Kim
authors.affiliation: Department of Ophthalmology, Severance Hospital, Institute of Vision Research, Yonsei University College of Medicine, Seoul, Korea Yonsei Healthcare Big Data-Based Knowledge Integration System Research Center and Institute of Convergence Science, Yonsei University College of Medicine, Seoul, Korea.
authors.forename: Sung Soo
authors.initials: SS
authors.lastname: Kim
mesh_terms: D000328:Adult; D001794:Blood Pressure / Q000502:physiology; D002829:Choroid / Q000033:anatomy & histology*; D005260:Female; D018475:Head-Down Tilt / Q000502:physiology*; D064368:Healthy Volunteers; D006339:Heart Rate / Q000502:physiology; D006801:Humans; D021621:Imaging, Three-Dimensional; D008297:Male; D009929:Organ Size; D011446:Prospective Studies; D041623:Tomography, Optical Coherence
keywords: Anatomy; Choroid; Imaging