Microgravity and Vision Impairments in Astronauts

Recent missions on board the International Space Station have revealed previously unreported physiological consequences of long duration space flight, particularly in eyesight, and in this Brief Dr. Seedhouse reviews the existing theories on what causes this degeneration and how long it will last. Notably, 60% of long-duration crews have reported subjective degradation in vision, a clear indication that further study is necessary before astronauts embark on even longer-term space missions. Decreased near-visual acuity was reported in 46% of ISS/Mir crewmembers, resulting in a change of up to 2 dioptres in their refractive correction. It is possible that ophthalmic changes have been present since the first days of spaceflight, but had been attributed to other causes; this approach to the issue as well as other hypotheses are all presented in full to give a broad foundation of the existing knowledge on the topic.  The changes have occurred at various times during a mission with varying degrees of visual degradation. Some cases resolved on return to Earth, but several crewmembers have not regained pre-flight visual acuity, indicating the damage may be permanent. One explanation of the syndrome has been attributed to hyperopic shift due to aging, but onboard analysis techniques, including visual acuity assessments, retinal imagery, and ultrasound examination of the eye, has led to the acceptance of a wider syndrome. In addition to vision changes, studies have reported flattening of the globe, swelling of the optic disc (papilledema), choroidal folds in the retina, swelling of the optic nerve sheath, and visual field defects. It is widely hypothesized that this spectrum of symptoms may be explained by an elevation of intracranial pressure (ICP). Establishing the provenance of this medical problem, monitoring its occurrence and resolving the symptoms for future long term space missions is a key challenge for space medicine. With this book, readers have an entrypoint for understanding the full scope of the problem and its possible origins.

Introduction.- Syndrome-specific Anatomy and Physiology.- Earth-bound Pathophysiology of Increased Intracranial Pressure.- Pathophysiology of Increased Intracranial Pressure in Weightlessness.- Pathology, demographics and anatomy of papilledema.- Microgravity Induced Cephalad Fluid Shift.- The Role of Carbon Dioxide.- Advanced Resistive Exercise Device (ARED).- Diet on board the International Space Station.

Erik Seedhouse is a Norwegian-Canadian suborbital astronaut whose life-long ambition is to work in space. After completing a degree in Sports Science the author joined the 2^nd Battalion the Parachute Regiment. During his time in the ‘Para’s’, Erik spent six months in Belize, where he was trained in the art of jungle warfare. Later, he spent several months learning the intricacies of desert warfare in Cyprus. He made 30+ jumps from a C130, performed 200+ helicopter abseils and fired more anti-tank weapons than he cares to remember! 

 

Upon returning to the comparatively mundane world of academia, the author embarked upon a Master’s in Medical Science, supporting his studies by winning prize money in 100 kilometer running races. After placing third in the World 100km Championships in 1992, the author turned to ultra-distance triathlon, winning the World Endurance Triathlon Championships in 1995 and 1996. For good measure, he won the World Double Ironman Championships and the Decatriathlon, an event requiring competitors to swim 38km, cycle 1800km, and run 422km. Non-stop!

 

Returning to academia, Erik pursued his Ph.D. at the German Space Agency’s Institute for Space Medicine. While studying he won Ultraman Hawai’i and the European Ultraman Championships and completed Race Across America. As the world’s leading ultra-distance triathlete Erik was featured in dozens of magazines and television interviews. In 1997, GQ magazine nominated him as the ‘Fittest Man in the World’.

 

In 1999, Erik retired from triathlon. In 2005 he worked as an astronaut training consultant for Bigelow Aerospace and wrote ‘Tourists in Space’. He is a Fellow of the British Interplanetary Society and a member of the Space Medical Association. In 2009, he was one of the final 30 candidates in the Canadian Space Agency’s Astronaut Recruitment Campaign. Erik works as a spaceflight instructor for the American

Astronautics Institute, professional speaker, triathlon coach, author, and Editor-in-Chief for the Handbook of Life Support Systems for Spacecraft. Between 2008 and 2013 he served as director of Canada’s manned centrifuge operations.

 

In addition to being a suborbital astronaut, triathlete, centrifuge operator, pilot and author, Erik is an avid mountaineer and is pursuing his goal of climbing the Seven Summits. This brief is his eighteenth book. When not writing, he spends as much time as possible in Kona on the Big Island of Hawai’i and at his real home in Sandefjord, Norway. Erik and his wife, Doina, are owned by three rambunctious cats – Jasper, Mini-Mach and Lava.