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Intraocular Pressure (DSO 472)
Principal Investigator
Research Area:
Cardiovascular physiology
Species Studied
Scientific Name: Homo sapiens Species: Human

Intraocular pressure (IOP) has been shown to be an objective and quantitative measure of fluid shifts toward the head in the 10-degree head-down tilt bed rest model of microgravity. However, insufficient numbers of measurements have been made in microgravity to correlate bed rest changes with changes that occur in weightlessness.

A study by Mader and Meehan (Mader et al., 1990) has quantified IOP changes that occurred with a 10-degree whole body head-down tilt over 48 hours. An immediate rise in IOP was documented upon assuming the head-down position. For the next 48 hours, variations in IOP were observed. Upon resuming the sitting position, there was a significant drop in IOP below the initial sitting values. The results of this study support the theory that distension of the retinal veins is a mechanism for the sudden changes in IOP that occur with changes in position. Assuming that head-down tilt is a valid model for fluid shifts in microgravity, the results from this study predict a similar sustained IOP increase in microgravity and a corresponding temporary drop in IOP (to below preflight values) upon return to Earth. Significant increases in IOP could result in visual impairment affecting crew performance and operations.

This study was designed to test the following hypothesis: Intraocular pressures will rise immediately upon entering microgravity due to fluid shifts toward the head, and will drop to below preflight levels upon return to 1-G. The objectives of this study were:

1. To establish a database of changes in intraocular pressures that can be used to evaluate crew health,
2. To validate 10-degree head-down tilt bed rest as a model for fluid shifts toward the head in microgravity,
3. To facilitate the interpretation of data by providing a quantitative measure of microgravity induced fluid shifts toward the head,
4. To validate the hand-held tonometer as an effective tool for diagnostic and scientific data collection that can be used in on orbit investigations.

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Mader TH, Gibson CR, Caputo M, Hunter N, Taylor G, Charles J, Meehan RT. Intraocular pressure and retinal vascular changes during transient exposure to microgravity. American Journal of Ophthalmology. 1993. March 15;115(3):347-50. []

Mader, TH. Intraocular pressure in microgravity. Journal of Clinical Pharmacology. 1991. October;31(10):947-50. []

Intraocular pressure

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Data Information
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Intraocular pressure

Mission/Study Information
Mission Launch/Start Date Landing/End Date Duration
STS-31 04/24/1990 04/29/1990 5 days
STS-32 01/09/1990 01/20/1990 11 days
STS-34 10/18/1989 10/23/1989 5 days
STS-41 10/06/1990 10/10/1990 4 days
STS-44 11/24/1991 12/01/1991 7 days
STS-50 06/25/1992 07/09/1992 14 days
STS-52 10/22/1992 11/01/1992 10 days
STS-53 12/02/1992 12/09/1992 7 days

Additional Information
Managing NASA Center
Johnson Space Center (JSC)
Responsible NASA Representative
Johnson Space Center LSDA Office
Project Manager: Pamela A. Bieri
Institutional Support
National Aeronautics and Space Administration (NASA)
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