Postural Variations of Intraocular Pressure - Preflight Experiments for the Di-Mission

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Abstract
Specific alterations in systemic circulation due to fluid shift in microgravity may lead to a rise in intraocular pressure (IOP). This situation can be simulated by head-down tilt. Several series of tonometry were performed using a handheld applanation tonometer: (1) Short time postural changes up to -90° head down and back. (2) A period of 2 h in -10° head down. (3) Repetition of series 2 after dehydration of the subjects. (4) Seven-day bedrest study in -7° head-down tilt. (5) A period of lower body negative pressure (LBNP). (6) Valsalva maneuver. Immediately on tilting, the IOP rises with hydrostatic pressure and returns to normal again after about 1 h. The IOP seems to change parallel to venous pressure. Further experiments are planned for Spacelab missions.

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