Retrobulbar fat, or the fat behind the eyeball, plays in important
role in eye motion.  In order to gain a better understanding of
retrobulbar fat mobility during eye motion, MRI datasets of the eyes
of a healthy subject were acquired during seven different gaze
directions.  The Demons deformable registration algorithm was used
to derive time-dependent three-dimensional deformation vector fields
from these datasets.  Visualisation techniques were applied to these
datasets in order to investigate fat mobility in specific regions of
interest.  In two of the three regions of interest, fat moved half
as fast as the embedded structures.  In other words, when the
muscles and the optic nerve that are embedded in the fat move, the
fat partly moves along with these structures and partly flows around
them.  This raises compelling research questions.