title: Effects of 30-day head-down bed rest on ocular structures and visual function in a healthy subject.
abstract: BACKGROUND
  We report ocular changes occurring in a healthy human subject enrolled in a bed rest (BR) study designed to replicate the effects of a low-gravity environment.
  
  
  METHODS
  A 25-yr-old Caucasian man spent 30 consecutive days in a 6 degrees head-down tilt (HDT) position at the NASA Flight Analogs Research Unit. Comprehensive ophthalmologic exams, optic disc stereo-photography, standard automated perimetry (SAP), and optic disc Spectralis OCT scans were performed at baseline, immediately post-BR (BR+0), and 6 mo post-BR.
  
  
  METHODS
  changes in best-corrected visual acuity, intraocular pressure (IOP), cycloplegic refraction, SAP, and Spectralis OCT measures. At BR+0 KIOP was 11 and 10 mmHg in the right (OD) and left eye (OS), respectively (a bilateral 4-mmHg decrease compared to baseline); SAP documented a possible bilateral symmetrical inferior scotoma; Spectralis OCT showed an average 19.4 microm (+5.2%) increase in peripapillary retinal thickness, and an average 0.03 mm3 (+5.0%) increase in peripapillary retinal volume bilaterally. However, there were no clinically detectable signs of optic disc edema. At 6 mo post-BR, IOP was 13 and 14 mmHg in OD and OS, respectively, and the scotoma had resolved. Spectralis OCT measurements matched the ones recorded at baseline.
  
  
  CONCLUSIONS
  In this subject, a reduction in IOP associated with subtle structural and functional changes compared to baseline were documented after prolonged head-down BR. These changes may be related to cephalad fluid shifts in response to tilt. Further studies should clarify whether decreased translaminar pressure (i.e., the difference between IOP and intracranial pressure) may be responsible for these findings.
authors: Department of Ophthalmology and Visual Sciences, The University of Texas Medical Branch, Galveston, TX 77555-1106, USA.
authors: Giovanni
authors: G
authors: Taibbi
authors: Kevin
authors: K
authors: Kaplowitz
authors: Ronita L
authors: RL
authors: Cromwell
authors: Bernard F
authors: BF
authors: Godley
authors: Susana B
authors: SB
authors: Zanello
authors: Gianmarco
authors: G
authors: Vizzeri
mesh_terms: D000328:Adult; D001510:Bed Rest; D003941:Diagnostic Techniques, Ophthalmological; D005123:Eye / Q000033:anatomy & histology*; D018495:Fluid Shifts / Q000502:physiology; D018475:Head-Down Tilt / Q000502:physiology; D006801:Humans; D007429:Intraocular Pressure / Q000502:physiology*; D008297:Male; D009901:Optic Nerve Diseases / Q000175:diagnosis; D014786:Vision Disorders / Q000209:etiology* / Q000503:physiopathology*; D018474:Weightlessness Simulation