title: 3D collagen orientation study of the human cornea using X-ray diffraction and femtosecond laser technology.
abstract: OBJECTIVE
  To study the distribution and predominant orientations of fibrillar collagen at different depths throughout the entire thickness of the human cornea. This information will form the basis of a full three-dimensional reconstruction of the preferred orientations of corneal lamellae.
  
  
  METHODS
  Femtosecond laser technology was used to delaminate the central zones of five human corneas into three separate layers (anterior, mid, and posterior stroma), each with predetermined thicknesses. Wide-angle x-ray diffraction was used to study the gross collagen fibril orientation and distribution within each layer.
  
  
  RESULTS
  The middle and posterior parts of the human cornea demonstrated a preferential orthogonal arrangement of collagen fibrils, directed along the superior-inferior and nasal-temporal meridians, with an increase in the number of lamellae toward the periphery. However, the anterior cornea (33% of total corneal thickness) showed no systematic preferred lamellar orientation.
  
  
  CONCLUSIONS
  In the posterior two thirds of the human cornea, collagen lies predominantly in the vertical and horizontal meridians (directed toward the four major rectus muscles), whereas collagen in the anterior third of the cornea is more isotropic. The predominantly orthogonal arrangement of collagen in the mid and posterior stroma may help to distribute strain in the cornea by allowing it to withstand the pull of the extraocular muscles, whereas the more isotropic arrangement in the anterior cornea may play an important role in the biomechanics of the cornea by resisting intraocular pressure while at the same time maintaining corneal curvature.
authors.affiliation: School of Optometry and Vision Sciences, Cardiff University, Cardiff, United Kingdom.
authors.forename: Mohammad
authors.initials: M
authors.lastname: Abahussin
authors.forename: Sally
authors.initials: S
authors.lastname: Hayes
authors.forename: Nathaniel E
authors.initials: NE
authors.lastname: Knox Cartwright
authors.forename: Christina S
authors.initials: CS
authors.lastname: Kamma-Lorger
authors.forename: Yasir
authors.initials: Y
authors.lastname: Khan
authors.forename: John
authors.initials: J
authors.lastname: Marshall
authors.forename: Keith M
authors.initials: KM
authors.lastname: Meek
mesh_terms: D003315:Cornea / Q000737:chemistry*; D024022:Fibrillar Collagens / Q000737:chemistry*; D006801:Humans; D007834:Lasers; D008968:Molecular Conformation; D014961:X-Ray Diffraction
chemical_list: D024022:Fibrillar Collagens