Heavier Astronauts Have Higher Risk of Post-flight Eye Changes

Heavier Astronauts Have Higher Risk of Post-flight Eye Changes

The results of a research project led by Dr. Jay Buckey of Dartmouth College have just been published, as described in this American Journal of Physiology press release.  The findings suggest that changes in the eye that occur during spaceflight may be related to how much an astronaut weighs. The study is published ahead of print in the American Journal of Physiology—Regulatory, Integrative and Comparative Physiology.  Creare LLC collaborated with Dartmouth to develop numerical models of the eye structure and the cerebrovascular/cerebrospinal circulation.

Spaceflight-Associated Neuro-ocular  Syndrome

Recently, awareness has increased over astronaut vision changes that occur during and after spaceflight. Reduced gravity levels (microgravity) in space can lead to spaceflight-associated neuro-ocular syndrome (SANS) in some astronauts. SANS refers to structural changes in the eye that may impair vision, including swelling of the optic nerve (optic disc edema) and colored indentations (choroidal folds) in the blood vessel network at the back of the eye. Researchers now think that how much a person weighs may play a role in these ocular changes.

The research team examined data collected by NASA from astronauts who had made long-duration space flights (averaging 165 days). The data included the astronauts’ sex and pre-flight height, weight, waist and chest size, as well as information about post-flight eye changes. The findings were related to body weight, not body mass index. They found that none of the female astronauts analyzed—who weighed less than the males—returned to Earth with symptoms of SANS. To rule out sex differences as a cause for the disparity, the researchers also examined the men’s data separately. “Pre-flight weight, waist circumference and chest circumference were all significantly greater in those who developed either disc edema or choroidal folds. This was still true when only the male cohort was analyzed,” the researchers wrote. “The results from this study show a strong relationship between body weight and the development of ocular changes in space.”

Creare developed, validated, and demonstrated a numerical model for simulating ocular physiology changes that occur in microgravity and that impact astronaut vision during and after spaceflight. The numerical modeling work was necessitated by the complexity of ocular anatomy and physiology and the difficulty of making detailed measurements on human subjects in microgravity.  A system-level model was developed as a series of networked fluid elements to represent the flow and pressure responses in the human body.   The system-level model was then linked to a detailed finite element model to describe stresses in the eye and the resulting geometry changes. Creare has used the model to predict the effects of body weight on ocular physiology suggested in the NASA astronaut data analysis.

You can read the full article, “Microgravity-induced ocular changes are related to body weight,” published ahead of print in the American Journal of Physiology—Regulatory, Integrative and Comparative Physiology.