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  • Astronaut optic nerve morphology unresponsive to brief lower body negative pressure

    Neuro-Ophthalmology/Orbit

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    Review of: Changes in optic nerve head and retinal morphology during spaceflight and acute fluid shift reversal

    Pardon L, Macias B, Ferguson C, et al. JAMA Ophthalmology, in press 2022

    Astronauts have been recently observed to develop papilledema, choroidal folds, and hyperopic shift during spaceflight, which is presumably due to the microgravity in space. Lowering body negative pressure (LBNP) has been proposed as a potential countermeasure for this phenomenon, called spaceflight-associated neuro-ocular syndrome (SANS). This study reports the results of LBNP from investigations on astronauts during their long-duration missions at the International Space Station.

    Study design

    This prospective cohort study included 14 astronauts who underwent OCT imaging before flight, in-flight, and up to 180 days after return to Earth. In-flight imaging was performed during normal weightless conditions and during 10–20 minutes of LBNP exposure.

    Outcomes

    On flight day 50, 4 of the 14 astronauts (29%) had observable optic disc edema on OCT as measured by an increase in peripapillary total retinal thickness. By flight day 150, 9 of 13 astronauts (69%) had observable optic disc edema on OCT, but only 1 astronaut had visible Frisen grade 1 optic disc edema. Overall, there was a significant increase in minimum rim width, decrease in cup volume, posterior displacement of Bruch membrane opening, and decrease in macular thickness, which returned to baseline 180 days after returning to Earth. LBNP of 25 mm Hg for 10–20 minutes did not change these ocular parameters.

    Limitations

    One of the limitations is the relatively small number of participants. In addition, OCT scans with and without LBNP were not done on the exact same day because of crew-scheduling constraints. In addition, LBNP was only done in 1 session for 10–20 minutes.

    Clinical significance

    This study confirms that mild optic disc edema occurs in the majority of astronauts during spaceflight. However, observation of the posterior displacement of Bruch membrane opening and a decrease in macular thickness shows that the pathophysiology is unlikely due to raised intracranial pressure. The study also showed that short duration LBNP did not mitigate the ocular changes, suggesting that longer duration treatment may be required and/or involvement of other factors. Understanding the ocular changes that occur during spaceflight and approaches to mitigation are important if we are to send astronauts on longer duration spaceflights.