Ophthalmic changes are associated with visual cortex functional network reorganization after 90-day head-down tilt...

Area of Science:

• Space Medicine
• Neuroscience
• Ophthalmology

Background:

• Microgravity causes fluid shifts, potentially leading to neuro-ophthalmological issues like optic disc edema.
• The long-term effects of simulated microgravity on eye health and visual cortex function are not fully understood.

Purpose of the Study:

• To investigate the impact of prolonged simulated microgravity on ophthalmic alterations.
• To explore the relationship between these changes and functional reorganization in the visual cortex.

Main Methods:

• 36 participants underwent 90-day head-down tilt bed rest (HDTBR) simulating microgravity.
• Ophthalmic tests (visual acuity, contrast sensitivity) and neuroimaging (fMRI for visual cortex connectivity, 3D-pcASL for ocular blood flow) were conducted.
• Assessments occurred at baseline, post-HDTBR, and after 28 days of recovery.

Main Results:

• A 90-day HDTBR simulation led to significant decreases in ocular blood flow (OBF), near visual acuity (NVA), and best-corrected visual acuity (BCVA).
• Functional connectivity (FC) increased within the visual cortex (V1) and between V1 and V3.
• Decreased BCVA correlated with reduced OBF and increased V1-V3 FC.

Conclusions:

• Reduced OBF may be a key factor in decreased visual acuity under simulated microgravity.
• Functional reorganization of the visual cortex appears linked to altered visual function and OBF.
• Extended recovery periods, potentially over a month, may be necessary to reverse these spaceflight-induced adaptations.