OUR CENTRAL OBJECTIVE IS TO USE EXISTING NOVEL METHODS THAT WE HAVE DEVELOPED TO EVALUATE THESE HYPOTHESES. FIRST WE WILL COMPUTE THE MECHANICAL PROPERTIES OF THE DURA MATER IN ASTRONAUTS SEE WHETHER THESE PROPERTIES ARE DIFFERENT THAN IN SUBJECTS WHO HAVE NOT BEEN IN SPACE AND SEE WHETHER THEY CORRELATE WITH THE SEVERITY OF SANS. TO DO SO WE WILL USE EXISTING SETS OF MR SCANS: ONE TAKEN WHEN THE ASTRONAUT IS LYING SUPINE AND THE OTHER TAKEN WHEN THE ASTRONAUT IS LYING IN 15 DEGREE HEAD-DOWN TILT. BY ANALYZING THESE IMAGES AND BUILDING A COMPUTATIONAL MODEL OF HOW THE OPTIC NERVE SHEATH EXPANDS AS FLUID PRESSURE CHANGES WITHIN IT DUE TO HEAD-DOWN TILT WE CAN OBTAIN A PARAMETER OF THE DURA MATER KNOWN AS THE STRUCTURAL STIFFNESS. SECOND WE WILL USE AN EXISTING COMPUTATIONAL MODEL TO DETERMINE STRAINS IN THE OPTIC NERVE HEAD DUE TO CHOROIDAL SWELLING SEE IF THESE STRAINS ARE LARGER THAN THOSE WHICH OCCUR ON EARTH AND SEE IF THEY ARE RELATED TO THE SEVERITY OF SANS IN ASTRONAUTS. CHOROIDAL SWELLING IN SPACE HAS ALREADY BEEN MEASURED USING OPTICAL IMAGING TECHNOLOGY AND THUS WE CAN IMMEDIATELY USE OUR MODELING APPROACH WITH THIS DATA SET. THIS WORK DIRECTLY ADDRESSES THE FOLLOWING STATED GOAL OF THE RFA: QUANTIFICATION OF THE CREW HEALTH AND PERFORMANCE RISKS ASSOCIATED WITH HUMAN SPACE-FLIGHT FOR THE VARIOUS EXPLORATION MISSIONS. MORE SPECIFICALLY IT ADDRESSES TWO NEEDS IDENTIFIED BY NASA RELATED TO SANS. FIRST WE DO NOT KNOW THE ETIOLOGICAL MECHANISMS AND CONTRIBUTING RISK FACTORS FOR OCULAR STRUCTURAL AND FUNCTIONAL CHANGES SEEN INFLIGHT AND POST FLIGHT AND THIS WORK COULD HELP DETERMINE SUCH FACTORS. SECOND WE NEED A SET OF VALIDATED AND MINIMALLY OBTRUSIVE DIAGNOSTIC TOOLS TO MEASURE AND MONITOR CHANGES IN INTRACRANIAL PRESSURE OCULAR STRUCTURE AND OCULAR FUNCTION. THE TOOLS WE PROPOSE TO USE WILL MEASURE THE FUNCTION OF A KEY OCULAR STRUCTURE NAMELY THE OPTIC NERVE SHEATH.