Changes in Optic Nerve Head and Retinal Morphology During Spaceflight and Acute Fluid Shift Reversal

Area of Science:

• Space Medicine
• Ophthalmology
• Physiology

Background:

• Spaceflight causes headward fluid shifts, potentially leading to spaceflight-associated neuro-ocular syndrome.
• Countermeasures reversing fluid shifts are crucial for mitigating these risks.

Purpose of the Study:

• To investigate if lower-body negative pressure (LBNP) mitigates ocular structural changes during spaceflight.
• To assess the impact of LBNP on optic nerve head and retinal morphology.

Main Methods:

• Prospective cohort study involving 14 crew members on 6-12 month International Space Station missions.
• Optical coherence tomography (OCT) scans of optic nerve head and macula were taken pre-flight, in-flight (with and without LBNP), and post-flight.
• Data analyzed from 2016-2021.

Main Results:

• Long-duration spaceflight (mean 214 days) was associated with increased optic nerve rim width, decreased optic cup volume, and reduced macular thickness.
• Acute in-flight exposure to 25-mm Hg LBNP did not significantly alter these ocular parameters.
• Posterior displacement of Bruch membrane opening was observed.

Conclusions:

• Spaceflight induces significant changes in optic nerve head and retinal structure.
• Brief LBNP application is insufficient to counteract these spaceflight-induced ocular alterations.
• Further research is needed to determine optimal LBNP duration or explore other mitigating factors.