illustration (IMAGE) UT Southwestern Medical Center Caption Body fluids in zero gravity apply constant pressure behind the eyes, causing progressive flattening of the eyeball, swelling of the optic nerve, and vision impairment. Credit UT Southwestern Medical Center Usage Restrictions none License Original content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.