Mader TH, Meehan RT, Hunter N, Taylor G.
Aviat Space Environ Med. 1989 May; 60: 492.
Univ. of Texas Medical Branch, Madigan Army Med Ctr, Galveston 77550.
INTRODUCTION. A rise in intraocular pressure (IOP) has been noted in head-down studies. We used this model for fluid shifts in microgravity to investigate diurnal IOP variations. METHODS. IOPs were measured in 9 subjects during 48 h of 10 degrees head-down tilt by using a pneumatonometer. IOPs were obtained: initially in a sitting position, immediately on assuming head-down, every 6 h during 48 h of head-down and immediately after the final head-down measurement. Visual acuities (VAs) were measured every 6 h by overhead projection. Retinal color photos were taken every 24 h by hand-held KOWA camera and analyzed by computer image analysis. RESULTS. A sudden rise in IOP (14.22 +/- .9mm Hg seated vs 18.89 +/- 1.15mm Hg head-down, p < .001) was recorded when head-down was assumed. During the next 48 h, diurnal variations were noted; initial and final head-down IOPs were not significantly different. When subjects resumed the sitting position, IOPs fell significantly below the initial sitting values (a difference of 3.06 +/- .92mm Hg, p < .001). Retinal vessel constriction was documented and VAs remained unchanged. CONCLUSIONS. Diurnal variations in IOP were recorded despite 48 h of head-down. An increase in choroidal blood volume may occur over 48 h of head-down with a compensatory decrease in aqueous volume. Retinal vessel autoregulation may cause vasoconstriction. VA was unimpaired despite a sudden and sustained 32% increase in IOP.
Publication Types:
Keywords:
- Circadian Rhythm
- Head
- Head-Down Tilt
- Intraocular Pressure
- Protons
- Retina
- Retinal Vessels
- Visual Acuity
- Weightlessness
- NASA Center JSC
- NASA Discipline Number 18-10
- NASA Discipline Regulatory Physiology
- NASA Program Biomedical Research
- Non-NASA Center
Other ID:
UI: 102212571
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