title: Subfoveal choroidal thickness and foveal retinal thickness during head-down tilt.
abstract: BACKGROUND
  To reveal subtle morphological changes in the eye during simulated microgravity for spaceflights, we measured subfoveal choroidal thickness and foveal retinal thickness during 10 degrees head-down tilt (HDT). We hypothesized that elevated ophthalmic vein pressure during simulated microgravity increases subfoveal choroidal thickness via enlargement of the choroidal vasculature and greater choroidal blood volume.
  
  
  METHODS
  The right eyes of nine healthy subjects (seven men, two women) were examined. Subfoveal choroidal thickness and foveal retinal thickness were measured using spectral domain-optical coherence tomography in the sitting position, and after 15 and 30 min of 10 degrees HDT. Intraocular pressure was also measured.
  
  
  RESULTS
  Mean subfoveal choroidal thickness (+/- SEM) increased from 300 +/- 31 microm in the sitting position to 315 +/- 31 microm with 15-min HDT, and 333 +/- 31 microm with 30-min HDT. However, no change in foveal retinal thickness was observed (228 +/- 9 microm in the sitting position, 228 +/- 10 microm with 15-min HDT and 228 +/- 9 microm with 30-min HDT). Intraocular pressure increased from 14 +/- 1 mmHg in the sitting position to 21 +/- 2 mmHg with 30-min HDT (54 +/- 6%, N = 5).
  
  
  CONCLUSIONS
  Subfoveal choroidal thickness and intraocular pressure were increased by HDT during simulated microgravity, although no change in foveal retinal thickness was observed.
authors.affiliation: Division of Ophthalmology, Department of Visual Science, Nihon University School of Medicine, Tokyo, Japan.
authors.forename: Ari
authors.initials: A
authors.lastname: Shinojima
authors.forename: Ken-Ichi
authors.initials: K
authors.lastname: Iwasaki
authors.forename: Ken
authors.initials: K
authors.lastname: Aoki
authors.forename: Yojiro
authors.initials: Y
authors.lastname: Ogawa
authors.forename: Ryo
authors.initials: R
authors.lastname: Yanagida
authors.forename: Mitsuko
authors.initials: M
authors.lastname: Yuzawa
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D002829:Choroid / Q000098:blood supply*; D004562:Electrocardiography; D005260:Female; D005584:Fovea Centralis / Q000098:blood supply*; D018475:Head-Down Tilt; D006801:Humans; D007429:Intraocular Pressure; D008297:Male; D008875:Middle Aged; D013026:Space Flight; D041623:Tomography, Optical Coherence; D014893:Weightlessness