Physiological cerebrospinal fluid interactions between brain and eye structures are altered after long-duration...

Area of Science:

• Neuroscience
• Ophthalmology
• Aerospace Medicine

Background:

• Long-duration spaceflight induces spaceflight-associated neuro-ocular syndrome (SANS), impacting vision and ocular structures.
• Astronauts experience brain adaptations, including ventricular expansion and cerebrospinal fluid (CSF) redistribution, but the link to ocular changes is unclear.

Purpose of the Study:

• To investigate the integrative physiological mechanisms linking brain and eye adaptations during spaceflight.
• To explore the relationship between third ventricle volume and ocular parameters in astronauts and control subjects.

Main Methods:

• Automated morphometric analysis of high-resolution MRI data from astronauts and terrestrial controls.
• Correlation analysis between third ventricle volume and ocular parameters (globe dimensions, optic nerve sheath volume, optic nerve length, retro-orbital width).

Main Results:

• Significant baseline correlations between third ventricle volume and multiple ocular parameters were observed in controls.
• Post-flight, astronauts showed increased optic nerve sheath volume and optic nerve length.
• Longitudinal analysis revealed third ventricle expansion correlated selectively with globe changes, not optic nerve sheath or retro-orbital width.

Conclusions:

• Spaceflight-induced microgravity creates differential biomechanical effects across orbital compartments, supporting CSF compartmentalization.
• The findings suggest a CSF-mediated coupling mechanism underlying SANS, limited by the cranial ceiling effect.
• This study quantifies the limits of brain tissue expansion during intracranial fluid shifts in astronauts.