title: Effects of prone and reverse trendelenburg positioning on ocular parameters.
abstract: BACKGROUND
  : In a pilot study of awake volunteers, intraocular pressure (IOP), choroid layer thickness, and optic nerve diameter were shown to increase in the prone position over 5 h with a nonsignificant trend of attenuation using a 4-degree increase of table inclination. These effects have previously not been isolated from anesthetic and fluid administration over a prolonged period, using an adequate sample size.
  
  
  METHODS
  : After institutional review board approval, 10 healthy volunteers underwent IOP measurement (Tono-Pen XL, Medtronic Solan, Jacksonville, FL) as well as choroidal thickness and optic nerve diameter assessment (Sonomed B-1000, Sonomed, Inc., Lake Success, NY, or the I System-ABD, Innovative Imaging, Inc., Sacramento, CA) on a Jackson table (Orthopedic Systems, Inc., Union City, CA), during 5 h horizontal prone and 5 h 4-degree reverse Trendelenburg positioning. Measurements were assessed as initial supine, initial prone, and hourly thereafter. Vital signs were recorded at each position and time point.
  
  
  RESULTS
  : IOP, choroidal thickness, and optic nerve diameter were observed to increase with time in the prone position. A small degree of reverse Trendelenburg attenuated the increase in choroidal thickness but not IOP or optic nerve diameter.
  
  
  CONCLUSIONS
  : Prolonged prone positioning increases IOP, choroid layer thickness, and optic nerve diameter independent of anesthetics and intravenous fluid infusion and 4 degrees of table inclination (15 cm of head to foot vertical disparity) may not attenuate these effects.
authors.affiliation: Department of Anesthesiology, New Jersey Medical School, University of Medicine and Dentistry of New Jersey, Newark, NJ 07103, USA. grantgp@umdnj.edu
authors.forename: Geordie P
authors.initials: GP
authors.lastname: Grant
authors.forename: Bernard C
authors.initials: BC
authors.lastname: Szirth
authors.forename: Henry L
authors.initials: HL
authors.lastname: Bennett
authors.forename: Sophia S
authors.initials: SS
authors.lastname: Huang
authors.forename: Rajesh S
authors.initials: RS
authors.lastname: Thaker
authors.forename: Robert F
authors.initials: RF
authors.lastname: Heary
authors.forename: Roger E
authors.initials: RE
authors.lastname: Turbin
mesh_terms: D000328:Adult; D001794:Blood Pressure / Q000502:physiology; D002829:Choroid / Q000502:physiology; D005123:Eye / Q000000981:diagnostic imaging; D005260:Female; D018475:Head-Down Tilt / Q000502:physiology*; D006339:Heart Rate / Q000502:physiology; D006801:Humans; D007429:Intraocular Pressure / Q000502:physiology; D008297:Male; D008875:Middle Aged; D015588:Observer Variation; D009799:Ocular Physiological Phenomena; D009900:Optic Nerve / Q000033:anatomy & histology; D010865:Pilot Projects; D016684:Prone Position / Q000502:physiology*; D015203:Reproducibility of Results; D018401:Sample Size; D016683:Supine Position / Q000502:physiology; D014463:Ultrasonography; D014792:Visual Acuity / Q000502:physiology; D055815:Young Adult