Space Headaches?! : NASA Looks at How Cephalad Fluid Shifts Affect Retinal Blood Vessels

On October 25th, 2017 (published by NASA in 2018), researchers at NASA’s Ames Research Center in Mountain View California explored the differences in pre and post vascular pressure in International Space Station Crew members and Head Down Tilted (HDT) Bed Rest patients. This study found that venous responses to these long-duration phenomena were marked by a decrease in vascular densities in the retinas of crew members and an increase in subjects after HDT. It is well known that long term space travelers experience “Space” headaches due to cephalad fluid shifts increasing fluid pressure in the upper body. Cephalad fluid shifts occur when an astronaut experiences more fluid then normal in their upper body due to the lack of gravity forcing the fluid down. This effect is easily seen in the puffy faces of astronauts in space.

Astronaut floating in space on the ISS
Astronaut Karen Nyberg floating in the International Space Station. You can somewhat see her puffier face in this image.

The researchers used a 30 infrared (IR) Heidelberg Spectralis® machine (a more advanced version of that fun puff test you get at the doctors) to determine that the vascular part of the retina in the eyes decreased in crew members after space flight yet increased in subjects after HDTBR. Pictures from Spectralis were looked at by VESGEN, a new automated software developed to discover vascular diseases in the retina and other tissue. The pictures created a map of blood vessel diameters and densities utilizing a new measure of vascular space-filling capacity called . The experiment used four people who experienced HDT and eight ISS crewmembers for the project. The VESGEN program performed two distinct tests on these individuals. Test one did not disclose if the left and right retinas were from the ISS travelers or HDT patients, while test two matched the pairs for each subject to display the effects of either HDT or space flight.

The researchers were surprised to see that 11 out of 16 retinas of the crew members’ space-filling capacity of their retinal vessels decreased and that 6 out of 10 retinas of the HDT patients vascular densities increased. The researchers believe that this difference mostly comes from lack of imaging that can capture smaller vessels rather than from vessel growth or decay. They also said that six months on the ISS compared to seventy days on HDT and the presence of microgravity and gravity may also have a large effect. However, there is still room to improve! The biostatistical and medical analyses of the images will have the final say on whether the VESGEN findings were correct or not.

OPINION: Who knew that main reason astronauts have space headaches was because of excess fluid on on their optic nerves! I think it’s very possible that VESGEN outcomes are true. As an aspiring optometrist myself, I found these results to be pretty cool. I’ve never really heard about the effects of almost no gravity on vision, but it makes sense right? Vision has to be compromised somehow with all of that extra fluid in the upper body. However it was a very small sample size so the VESGEN outcomes might be wrong, but then again its expensive to send people to space and hard to get people to do HDT for seventy days.


Murray, M.C., Vizzeri, G., Taibbi, G., Mason, S. S., Young, M. H., Zanello, S. B., and Parsons-Wingerter, P. A. 2018. Differences in Pre and Post Vascular Patterning of Retinas from ISS Crew Members and HDT Subjects by VESGEN Analysis. NASA Technical Reports Server: JSC-CN-40700.

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