title: Magic angle-enhanced MRI of fibrous microstructures in sclera and cornea with and without intraocular pressure loading.
abstract: OBJECTIVE
  The structure and biomechanics of the sclera and cornea are central to several eye diseases such as glaucoma and myopia. However, their roles remain unclear, partly because of limited noninvasive techniques to assess their fibrous microstructures globally, longitudinally, and quantitatively. We hypothesized that magic angle-enhanced magnetic resonance imaging (MRI) can reveal the structural details of the corneoscleral shell and their changes upon intraocular pressure (IOP) elevation.
  
  
  METHODS
  Seven ovine eyes were extracted and fixed at IOP = 50 mm Hg to mimic ocular hypertension, and another 11 eyes were unpressurized. The sclera and cornea were scanned at different angular orientations relative to the main magnetic field inside a 9.4-Tesla MRI scanner. Relative MRI signal intensities and intrinsic transverse relaxation times (T2 and T2*) were determined to quantify the magic angle effect on the corneoscleral shells. Three loaded and eight unloaded tendon samples were scanned as controls.
  
  
  RESULTS
  At magic angle, high-resolution MRI revealed distinct scleral and corneal lamellar fibers, and light/dark bands indicative of collagen fiber crimps in the sclera and tendon. Magic angle enhancement effect was the strongest in tendon and the least strong in cornea. Loaded sclera, cornea, and tendon possessed significantly higher T2 and T2* than unloaded tissues at magic angle.
  
  
  CONCLUSIONS
  Magic angle-enhanced MRI can detect ocular fibrous microstructures without contrast agents or coatings and can reveal their MR tissue property changes with IOP loading. This technique may open up new avenues for assessment of the biomechanical and biochemical properties of ocular tissues in aging and in diseases involving the corneoscleral shell.
authors.affiliation: NeuroImaging Laboratory, University of Pittsburgh, Pittsburgh, Pennsylvania, United States.
authors.forename: Leon C
authors.initials: LC
authors.lastname: Ho
authors.affiliation: UPMC Eye Center, Ophthalmology and Visual Science Research Center, Department of Ophthalmology, School of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania, United States Department of Bioengineering, Swanson School of Engineering, University of Pittsburgh, Pittsburgh, Pennsylvania, United States.
authors.forename: Ian A
authors.initials: IA
authors.lastname: Sigal
authors.affiliation: UPMC Eye Center, Ophthalmology and Visual Science Research Center, Department of Ophthalmology, School of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania, United States Department of Bioengineering, Swanson School of Engineering, University of Pittsburgh, Pittsburgh, Pennsylvania, United States.
authors.forename: Ning-Jiun
authors.initials: NJ
authors.lastname: Jan
authors.affiliation: Medical Robotics Lab, College of Engineering, University of Georgia, Athens, Georgia, United States.
authors.forename: Alexander
authors.initials: A
authors.lastname: Squires
authors.affiliation: Medical Robotics Lab, College of Engineering, University of Georgia, Athens, Georgia, United States.
authors.forename: Zion
authors.initials: Z
authors.lastname: Tse
authors.affiliation: Department of Electrical and Electronic Engineering, The University of Hong Kong, Pokfulam, Hong Kong, China.
authors.forename: Ed X
authors.initials: EX
authors.lastname: Wu
authors.affiliation: NeuroImaging Laboratory, University of Pittsburgh, Pittsburgh, Pennsylvania, United States Department of Bioengineering, Swanson School of Engineering, University of Pittsburgh, Pittsburgh, Pennsylvania, United States McGowan Institute for Regenerative Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania, United States Center for the Neural Basis of Cognition, University of Pittsburgh and Carnegie Mellon University, Pittsburgh, Pennsylvania, United States.
authors.forename: Seong-Gi
authors.initials: SG
authors.lastname: Kim
authors.affiliation: UPMC Eye Center, Ophthalmology and Visual Science Research Center, Department of Ophthalmology, School of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania, United States Department of Bioengineering, Swanson School of Engineering, University of Pittsburgh, Pittsburgh, Pennsylvania, United States Clinical and Translational Science Institute, University of Pittsburgh, Pittsburgh, Pennsylvania, United States.
authors.forename: Joel S
authors.initials: JS
authors.lastname: Schuman
authors.affiliation: NeuroImaging Laboratory, University of Pittsburgh, Pittsburgh, Pennsylvania, United States UPMC Eye Center, Ophthalmology and Visual Science Research Center, Department of Ophthalmology, School of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania, United States Department of Bioengineering, Swanson School of Engineering, University of Pittsburgh, Pittsburgh, Pennsylvania, United States Center for the Neural Basis of Cognition, University of Pittsburgh and Carnegie Mellon University, Pittsburgh, Pennsylvania, United States.
authors.forename: Kevin C
authors.initials: KC
authors.lastname: Chan
mesh_terms: D000818:Animals; D003094:Collagen / Q000648:ultrastructure*; D003315:Cornea / Q000502:physiology* / Q000648:ultrastructure; D006801:Humans; D007429:Intraocular Pressure / Q000502:physiology*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D023421:Models, Animal; D008954:Models, Biological; D012590:Sclera / Q000502:physiology* / Q000648:ultrastructure; D012756:Sheep
chemical_list: D003094:Collagen
keywords: cornea; magic angle effect; magnetic resonance imaging; ocular hypertension; sclera
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