NASA is closely monitoring a problem with the eyesight of astronauts who spend a long period in space. Approximately 60% of the astronauts who have spent more than a month in space suffer from intracranial hypertension. This condition is caused by fluid pressure in the skull. This flattening has caused astronauts problems so severe that they can no longer focus correctly. Many astronauts returning to Earth must get glasses for the first time. For others, the problem is so severe that it cannot be corrected. For some astronauts, they can no longer pass the eye exam to get their pilot’s license. Doctors believe the problem is caused by a buildup in fluid in the eyes during the astronauts’ time in flight. Normally, the fluid is pulled down by gravity.
Additionally, 20 percent of the astronauts showed a flattening in the rear of their eyeballs. Almost 33 percent of the astronauts studied also showed an expansion of the space around the optic nerve. This space is normally filled with cerebral spinal fluid. Some astronauts find that the problem corrects itself shortly after returning to earth. Others find that the problem never corrects itself.
Doctors warn that these problems must be further evaluated before longer trips in space can be carried out. Doctors at the University of Texas also warn that astronauts appear to be at greater danger of head trauma upon returning to Earth.
Studies have shown that the human heart could be changed in space, too. According to astrobiologists, it shrinks and pumps less blood. When an astronaut is exposed to microgravity, the blood travels from the lower body to the heart and the head, making the heart larger temporarily. The body interprets this change as an increase of blood volume and tries to expel the excess of fluid through urination, but also the heart shrinks in order to pump less blood. That’s the reason why astronauts feel dizziness when return to Earth.
Image: SCIENCE PHOTO LIBRARY Spacewalk. Composite image of an astronaut floating free during aspacewalk against a backdrop of cloud systems on Earth. A spacewalk is also known as ExtraVehicular Activity (EVA). Astronaut photographed during a space shuttle mission; the spacecraft can be seen reflected in his visor.