Optic disc edema develops in astronauts during long-duration spaceflight and is a risk for all future space travelers. Researchers based in Houston thought a ground-based analog of weightlessness that reproduces critical features of spaceflight-associated neuro-ocular syndrome would help facilitate a better understanding of the condition, as well as help clinicians prevent and treat it. However, their study found that while participants both in space and in simulation experienced a long-term mild elevation in intracranial pressure, small differences in the magnitude of pressure might dictate the severity of optic disc edema.

The study analyzed 11 healthy test participants before, during and after 30 days of strict 6° head-down tilt bed rest (the traditional spaceflight analog) along with 20 astronauts before and during approximately 30 days of spaceflight. The researchers collected data from the NASA Johnson Space Center, the German Aerospace Center and on board the International Space Station.

Peripapillary total retinal thickness increased to a greater degree (a mean difference of 37μm) among those on bed rest compared with the astronauts. Conversely, choroid thickness did not increase among those exposed to bed rest but increased among the astronauts—a mean difference of 27μm.

The researchers suggest that mild, long-term elevation in intracranial pressure experienced by individuals on bed rest is greater than the intracranial pressure experienced by astronauts, which could lead to the development of worse optic disc edema in individuals participating in the bed rest analogue. Still, they believe that developing their model of optic disc edema will be valuable for investigating countermeasures to protect astronauts and for studying the early onset of this pathologic condition, which is limited in symptomatic patients presenting with more advanced disease.

Laurie SS, Lee SMC, Macias BR, et al. Optic disc edema and choroidal engorgement in astronauts during spaceflight and individuals exposed to bed rest. JAMA Ophthalmol. December 26, 2019. [Epub ahead of print].