Ocular outcomes evaluation in a 14-day head-down bed rest study

Area of Science:

• Space medicine
• Ophthalmology
• Human physiology

Background:

• Microgravity poses risks to astronaut vision.
• Head-down tilt bed rest (HDTBR) simulates microgravity effects.
• Understanding ocular changes is crucial for spaceflight safety.

Purpose of the Study:

• To evaluate ocular outcomes during a 14-day head-down tilt bed rest (HDTBR) study.
• To assess changes in visual acuity, intraocular pressure, and retinal structure.
• To determine the safety of short-term HDTBR for ocular health.

Main Methods:

• 16 healthy subjects underwent 14 days of 6° HDT bed rest.
• Ophthalmological examinations included visual acuity, intraocular pressure (IOP), and Spectral-domain OCT.
• Pre/post-BR and in-bed measurements were compared using statistical tests.

Main Results:

• Near best-corrected visual acuity (BCVA) slightly improved; spherical equivalent shifted.
• Intraocular pressure (IOP) showed a small, transient increase (+3.03 mmHg).
• Retinal nerve fiber layer thickness (RNFLT) increased, particularly in the temporal-inferior and nasal-inferior quadrants, without optic disc edema.

Conclusions:

• 14-day HDTBR caused minor, non-progressive ocular changes.
• Improved BCVA may be due to a learning effect.
• Transient IOP elevation and RNFL thickening occurred, returning to baseline post-study.