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 entry point for understanding the full scope of the
problem and its possible origins.
