title: Collagen fibrils appear more closely packed in the prepupillary cornea: optical and biomechanical implications.
abstract: OBJECTIVE
  The size and organization of stromal collagen fibrils influence the biomechanical and optical properties of the cornea and hence its function. How fibrillar structure varies with position across the cornea has not been fully characterized. The present study was designed to quantify the collagen fibril spacing and diameter across the normal human cornea and to relate this to the properties of the tissue.
  
  
  METHODS
  Small-angle x-ray diffraction was used to map in detail the variation in fibril spacing and fibril diameter along orthogonal medial-lateral and inferior-superior meridians of five normal human corneoscleral discs.
  
  
  RESULTS
  Mean fibril diameters remained constant across all corneas up to the limbus, whereupon a sharp increase was observed. However, mean fibril spacing across the central 4 x 3 mm (prepupillary) cornea measured 5% to 7% lower than in the peripheral cornea.
  
  
  CONCLUSIONS
  Collagen fibrils in the prepupillary cornea appear to be more closely packed than in the peripheral cornea. Anisotropy in fibril packing across the cornea has potential implications for the transparency and refractive index of the tissue. Biomechanically, it is possible that the higher packing density of stress-bearing collagen fibrils in the prepupillary cornea is necessary for maintaining corneal strength, and hence curvature, in a region of reduced tissue thickness. By inference, these results could have important implications for the development of corneal models for refractive surgery.
authors.affiliation: Department of Optometry and Vision Sciences, Cardiff University, Cardiff, Wales, United Kingdom. bootec@cf.ac.uk
authors.forename: Craig
authors.initials: C
authors.lastname: Boote
authors.forename: Sally
authors.initials: S
authors.lastname: Dennis
authors.forename: Richard H
authors.initials: RH
authors.lastname: Newton
authors.forename: Hina
authors.initials: H
authors.lastname: Puri
authors.forename: Keith M
authors.initials: KM
authors.lastname: Meek
mesh_terms: D001696:Biomechanical Phenomena; D003094:Collagen / Q000737:chemistry* / Q000502:physiology; D003319:Corneal Stroma / Q000737:chemistry* / Q000502:physiology; D006801:Humans; D014961:X-Ray Diffraction
chemical_list: D003094:Collagen