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Changes in intraocular pressure during prolonged (7-day) head-down tilt bedrest.
Christophe Chiquet1, Marc-Antoine Custaud, Anne Pavy Le Traon
1Department of Ophthalmology, Edouard Herriot Hospital, Claude-Bernard Lyon 1 University, Lyon, France.
Journal of Glaucoma
|June 5, 2003
Summary
Intraocular pressure (IOP) temporarily increases when lying down but decreases during prolonged head-down tilt bedrest. This suggests the eyes may adapt to sustained postural changes, possibly due to dehydration or hormonal shifts.
Area of Science:
- Ophthalmology
- Physiology
- Aerospace Medicine
Background:
- Intraocular pressure (IOP) regulation is crucial for ocular health.
- Postural changes can influence IOP, with implications for conditions like glaucoma.
- Understanding these effects is important for spaceflight and prolonged bedrest scenarios.
Purpose of the Study:
- To investigate the acute and chronic effects of postural changes on intraocular pressure in healthy young women.
- To examine the relationship between intraocular pressure, corneal thickness, and physiological parameters during head-down tilt bedrest.
Main Methods:
- Noncontact tonometry measured IOP in 25 female volunteers in sitting and supine positions.
- Eight female volunteers underwent a 7-day -6 degrees head-down tilt (HDT) with IOP and corneal thickness monitored.
- Blood pressure, hematocrit, plasma volume, osmolality, and catecholamines were also measured.
Main Results:
- Supine position significantly increased IOP compared to sitting (P < 0.001).
- During 7-day HDT, IOP significantly decreased by day 5 and 7 (P = 0.03, P = 0.02).
- Corneal thickness increased significantly during HDT (P < 0.0001), and IOP returned to baseline post-HDT.
Conclusions:
- Healthy women's eyes adapt to prolonged head-down tilt bedrest, showing a slight IOP decrease.
- These adaptations may involve ocular dehydration or systemic cardiovascular and hormonal changes.
- The findings offer insights into ocular responses during sustained altered body positions.