Understanding the effects of microgravity on the human body is essential in enabling astronauts to travel through the harsh environment of space for months, or even years. Significant changes to the body's skeletal and muscle systems have been studied for decades, and strategies to maintain physical fitness are being applied through various countermeasures, including vigorous exercise, aboard the International Space Station. But scientists and researchers still have a lot to learn—including how time spent in space affects the eyes and brain.

Even during a trip as short as two weeks, vision changes occur for about a one-third of American astronauts. When the trip is longer—say, four to six months—that figure may double. But, before potential solutions can be proposed, scientists first have to understand what's causing these changes.

On Earth, gravity forces a body's natural blood volume downward, below the waist. Our heart forces it back up to the areas above the waist, including our eyes. But, what happens to that volume of blood and other fluids when gravity is no longer pulling them down?

The human body has an amazing ability to adapt.