title: Visualization of Sliding and Deformation of Orbital Fat During Eye Rotation.
abstract: OBJECTIVE
  Little is known about the way orbital fat slides and/or deforms during eye movements. We compared two deformation algorithms from a sequence of MRI volumes to visualize this complex behavior.
  
  
  METHODS
  Time-dependent deformation data were derived from motion-MRI volumes using Lucas and Kanade Optical Flow (LK3D) and nonrigid registration (B-splines) deformation algorithms. We compared how these two algorithms performed regarding sliding and deformation in three critical areas: the sclera-fat interface, how the optic nerve moves through the fat, and how the fat is squeezed out under the tendon of a relaxing rectus muscle. The efficacy was validated using identified tissue markers such as the lens and blood vessels in the fat.
  
  
  RESULTS
  Fat immediately behind the eye followed eye rotation by approximately one-half. This was best visualized using the B-splines technique as it showed less ripping of tissue and less distortion. Orbital fat flowed around the optic nerve during eye rotation. In this case, LK3D provided better visualization as it allowed orbital fat tissue to split. The resolution was insufficient to visualize fat being squeezed out between tendon and sclera.
  
  
  CONCLUSIONS
  B-splines performs better in tracking structures such as the lens, while LK3D allows fat tissue to split as should happen as the optic nerve slides through the fat. Orbital fat follows eye rotation by one-half and flows around the optic nerve during eye rotation.
  
  
  CONCLUSIONS
  Visualizing orbital fat deformation and sliding offers the opportunity to accurately locate a region of cicatrization and permit an individualized surgical plan.
authors.affiliation: Department of Ophthalmology Erasmus Medical Center, Rotterdam, the Netherlands.
authors.forename: Gijsbert J
authors.initials: GJ
authors.lastname: Hötte
authors.affiliation: Department of Mediamatics, Technical University Delft, Delft, the Netherlands.
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Schaafsma
authors.affiliation: Department of Mediamatics, Technical University Delft, Delft, the Netherlands ; Department of Radiology, Laboratory for Clinical and Experimental Image Processing, Leiden University Medical Center, Leiden, the Netherlands.
authors.forename: Charl P
authors.initials: CP
authors.lastname: Botha
authors.affiliation: Department of Radiology, Erasmus Medical Center, Rotterdam, the Netherlands.
authors.forename: Piotr A
authors.initials: PA
authors.lastname: Wielopolski
authors.affiliation: Department of Ophthalmology Erasmus Medical Center, Rotterdam, the Netherlands.
authors.forename: Huibert J
authors.initials: HJ
authors.lastname: Simonsz
keywords: eye movements; nonrigid registration; optical flow; orbital fat; soft tissue deformation