title: Comparison of retinal and choriocapillaris thicknesses following sitting to supine transition in healthy individuals and patients with age-related macular degeneration.
abstract: OBJECTIVE
  The effects of position on retinal and choroidal structure are absent from the literature yet may provide insights into disease states such as age-related macular degeneration (AMD).
  
  
  OBJECTIVE
  To evaluate the effect of postural change on retinal and choroidal structures in healthy volunteers and patients with non-neovascular AMD.
  
  
  METHODS
  Prospective observational case series at an academic tertiary care retina service from September 2013 to April 2014 involving 4 unaffected volunteers (8 eyes) and 7 patients (8 eyes) with intermediate AMD. Healthy volunteers selected for the study had no evidence of ocular disease. Patients with AMD were required to have at least 10 intermediate-sized drusen.
  
  
  METHODS
  Spectral-domain optical coherence tomography with enhanced depth imaging in upright (sitting) and supine positions. Stable imaging was achieved using a rotating adjustable mechanical arm that we constructed to allow the optical coherence tomography transducer to rotate 90°. The Iowa Reference Algorithms were used to quantify choroid and choriocapillaris thicknesses.
  
  
  METHODS
  Changes in sitting and supine position central macular thickness (in micrometers), total macular volume (in cubic millimeters), choroidal thickness (in micrometers), and choriocapillaris-equivalent thickness (CCET, in micrometers).
  
  
  RESULTS
  Choriocapillaris-equivalent thickness was thinner in healthy participants (9.89 μm; range, 7.15-12.5 μm) compared with patients with intermediate AMD (16.73 μm; range, 10.31-27.38 μm) (P = .02); there was no difference in overall choroidal thickness between the 2 groups (P = .38). There was a 15% CCET reduction among healthy participants when transitioning from a sitting (9.89 μm) to supine (8.4 μm; range, 6.92-10.7 μm) position (P = .02) vs a CCET reduction of 11.1% from sitting (16.73 μm) to supine (14.88 μm; range, 8.76-20.8 μm) positioning (P = .10) in patients with intermediate AMD.
  
  
  CONCLUSIONS
  Intermediate AMD appears to be associated with an increase in CCET and with a lack of positional responses that are observed in the CCET of normal eyes. Our results suggest that although outer portions of the choroid do not appear to be responsive to modest positional or hydrostatic pressure, the choriocapillaris capacity is, and this is measurable in vivo. Whether this physiologic deviation that occurs in AMD is related to atrophy, inflammation, or changes in autoregulatory factors or growth factors remains to be determined.
authors.affiliation: Vitreoretinal Service, Department of Ophthalmology and Visual Sciences, University of Iowa Hospitals and Clinics, Iowa City.
authors.forename: David R P
authors.initials: DR
authors.lastname: Almeida
authors.affiliation: The Stephen A. Wynn Institute for Vision Research, University of Iowa, Iowa City.
authors.forename: Li
authors.initials: L
authors.lastname: Zhang
authors.affiliation: Vitreoretinal Service, Department of Ophthalmology and Visual Sciences, University of Iowa Hospitals and Clinics, Iowa City.
authors.forename: Eric K
authors.initials: EK
authors.lastname: Chin
authors.affiliation: The Stephen A. Wynn Institute for Vision Research, University of Iowa, Iowa City.
authors.forename: Robert F
authors.initials: RF
authors.lastname: Mullins
authors.affiliation: The Stephen A. Wynn Institute for Vision Research, University of Iowa, Iowa City.
authors.forename: Murat
authors.initials: M
authors.lastname: Kucukevcilioglu
authors.affiliation: Vitreoretinal Service, Department of Ophthalmology and Visual Sciences, University of Iowa Hospitals and Clinics, Iowa City.
authors.forename: D Brice
authors.initials: DB
authors.lastname: Critser
authors.affiliation: The Stephen A. Wynn Institute for Vision Research, University of Iowa, Iowa City.
authors.forename: Milan
authors.initials: M
authors.lastname: Sonka
authors.affiliation: Vitreoretinal Service, Department of Ophthalmology and Visual Sciences, University of Iowa Hospitals and Clinics, Iowa City2The Stephen A. Wynn Institute for Vision Research, University of Iowa, Iowa City.
authors.forename: Edwin M
authors.initials: EM
authors.lastname: Stone
authors.affiliation: Vitreoretinal Service, Department of Ophthalmology and Visual Sciences, University of Iowa Hospitals and Clinics, Iowa City.
authors.forename: James C
authors.initials: JC
authors.lastname: Folk
authors.affiliation: Vitreoretinal Service, Department of Ophthalmology and Visual Sciences, University of Iowa Hospitals and Clinics, Iowa City2The Stephen A. Wynn Institute for Vision Research, University of Iowa, Iowa City3Iowa Institute for Biomedical Imaging, Iowa City4V.
authors.forename: Michael D
authors.initials: MD
authors.lastname: Abràmoff
authors.affiliation: Vitreoretinal Service, Department of Ophthalmology and Visual Sciences, University of Iowa Hospitals and Clinics, Iowa City2The Stephen A. Wynn Institute for Vision Research, University of Iowa, Iowa City.
authors.forename: Stephen R
authors.initials: SR
authors.lastname: Russell
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D002196:Capillaries / Q000473:pathology; D002829:Choroid / Q000098:blood supply*; D005260:Female; D005451:Fluorescein Angiography; D064368:Healthy Volunteers; D006801:Humans; D008297:Male; D008875:Middle Aged; D011187:Posture; D011446:Prospective Studies; D012160:Retina / Q000473:pathology*; D041623:Tomography, Optical Coherence; D057135:Wet Macular Degeneration / Q000503:physiopathology*