title: Acute effects of changes to the gravitational vector on the eye.
abstract: Intraocular pressure (IOP) initially increases when an individual enters microgravity compared with baseline values when an individual is in a seated position. This has been attributed to a headward fluid shift that increases venous pressures in the head. The change in IOP exceeds changes measured immediately after moving from seated to supine postures on Earth, when a similar fluid shift is produced. Furthermore, central venous and cerebrospinal fluid pressures are at or below supine position levels when measured initially upon entering microgravity, unlike when moving from seated to supine postures on Earth, when these pressures increase. To investigate the effects of altering gravitational forces on the eye, we made ocular measurements on 24 subjects (13 men, 11 women) in the seated, supine, and prone positions in the laboratory, and upon entering microgravity during parabolic flight. IOP in microgravity (16.3 ± 2.7 mmHg) was significantly elevated above values in the seated (11.5 ± 2.0 mmHg) and supine (13.7 ± 3.0 mmHg) positions, and was significantly less than pressure in the prone position (20.3 ± 2.6 mmHg). In all measurements,P< 0.001. Choroidal area was significantly increased in subjects in a microgravity environment (P< 0.007) compared with values from subjects in seated (increase of 0.09 ± 0.1 mm(2)) and supine (increase of 0.06 ± 0.09 mm(2)) positions. IOP results are consistent with the hypothesis that hydrostatic gradients affect IOP, and may explain how IOP can increase beyond supine values in microgravity when central venous and intracranial pressure do not. Understanding gravitational effects on the eye may help develop hypotheses for how microgravity-induced visual changes develop.
authors.affiliation: Giesel School of Medicine at Dartmouth College, Lebanon, New Hampshire; and.
authors.forename: Allison P
authors.initials: AP
authors.lastname: Anderson
authors.affiliation: Giesel School of Medicine at Dartmouth College, Lebanon, New Hampshire; and.
authors.forename: Jacob G
authors.initials: JG
authors.lastname: Swan
authors.affiliation: Creare LLC, Hanover, New Hampshire.
authors.forename: Scott D
authors.initials: SD
authors.lastname: Phillips
authors.affiliation: Creare LLC, Hanover, New Hampshire.
authors.forename: Darin A
authors.initials: DA
authors.lastname: Knaus
authors.affiliation: Creare LLC, Hanover, New Hampshire.
authors.forename: Nicholas T
authors.initials: NT
authors.lastname: Kattamis
authors.affiliation: Giesel School of Medicine at Dartmouth College, Lebanon, New Hampshire; and.
authors.forename: Christine M
authors.initials: CM
authors.lastname: Toutain-Kidd
authors.affiliation: Giesel School of Medicine at Dartmouth College, Lebanon, New Hampshire; and.
authors.forename: Michael E
authors.initials: ME
authors.lastname: Zegans
authors.affiliation: Giesel School of Medicine at Dartmouth College, Lebanon, New Hampshire; and.
authors.forename: Abigail M
authors.initials: AM
authors.lastname: Fellows
authors.affiliation: Giesel School of Medicine at Dartmouth College, Lebanon, New Hampshire; and Jay.C.Buckey.Jr@dartmouth.edu.
authors.forename: Jay C
authors.initials: JC
authors.lastname: Buckey
mesh_terms: D000328:Adult; D005123:Eye / Q000503:physiopathology*; D005260:Female; D006801:Humans; D007427:Intracranial Pressure / Q000502:physiology; D007429:Intraocular Pressure / Q000502:physiology; D008297:Male; D016684:Prone Position / Q000502:physiology*; D016683:Supine Position / Q000502:physiology*; D014690:Venous Pressure / Q000502:physiology; D014893:Weightlessness
keywords: choroidal area; hydrostatic gradient; intraocular pressure; visual impairment and intracranial pressure