Some ocular changes in astronauts are reversible upon return to Earth

This study monitored ocular structural changes in astronauts caused by long-term spaceflight.

Study design

In this longitudinal prospective cohort study, investigators evaluated the ocular health of 11 astronauts before, during and after 6-month missions on board the International Space Station. The study used OCT to determine the effects of spaceflight-associated neuro-ocular syndrome.

Outcomes

The optic nerve head rim tissue and peripapillary choroidal thickness both increased during spaceflight, with the majority of changes occurring during the first 90 days. At flight day 150, the mean optic nerve head rim tissue thickness and choroidal thickness increased by 35.7 µm (10% change) and 43 µm (18% change), respectively. These changes reverted to normal over 90 days following the astronauts’ return to Earth.

The axial eye length and anterior chamber depth decreased by a mean of 0.08 mm and 0.09 mm, respectively, when measured upon return to Earth and these changes persisted for at least 1 year. These structural changes resulted in a hyperopic shift. 

Limitations

The primary limitation of the study was the small number of participants. In addition, the optical biometry for measuring axial eye length was not conducted during spaceflight.

Clinical significance

This was the first study to report the time course and recovery of ocular changes that develop in astronauts during spaceflight, which may provide insight into the mechanism of spaceflight-associated neuro-ocular syndrome. It demonstrates that the retinal and choroidal thickening is reversible upon returning to Earth, but the axial length and hyperopic shifts can be permanent. These findings are important as we prepare for longer spaceflight missions to Mars and beyond.