title: Glaucoma-related Changes in the Mechanical Properties and Collagen Micro-architecture of the Human Sclera.
abstract: OBJECTIVE
  The biomechanical behavior of the sclera determines the level of mechanical insult from intraocular pressure to the axons and tissues of the optic nerve head, as is of interest in glaucoma. In this study, we measure the collagen fiber structure and the strain response, and estimate the material properties of glaucomatous and normal human donor scleras.
  
  
  METHODS
  Twenty-two posterior scleras from normal and diagnosed glaucoma donors were obtained from an eyebank. Optic nerve cross-sections were graded to determine the presence of axon loss. The specimens were subjected to pressure-controlled inflation testing. Full-field displacement maps were measured by digital image correlation (DIC) and spatially differentiated to compute surface strains. Maps of the collagen fiber structure across the posterior sclera of each inflated specimen were obtained using synchrotron wide-angle X-ray scattering (WAXS). Finite element (FE) models of the posterior scleras, incorporating a specimen-specific representation of the collagen structure, were constructed from the DIC-measured geometry. An inverse finite element analysis was developed to estimate the stiffness of the collagen fiber and inter-fiber matrix.
  
  
  RESULTS
  The differences between glaucoma and non-glaucoma eyes were small in magnitude. Sectorial variations of degree of fiber alignment and peripapillary scleral strain significantly differed between normal and diagnosed glaucoma specimens. Meridional strains were on average larger in diagnosed glaucoma eyes compared with normal specimens. Non-glaucoma specimens had on average the lowest matrix and fiber stiffness, followed by undamaged glaucoma eyes, and damaged glaucoma eyes but the differences in stiffness were not significant.
  
  
  CONCLUSIONS
  The observed biomechanical and microstructural changes could be the result of tissue remodeling occuring in glaucoma and are likely to alter the mechanical environment of the optic nerve head and contribute to axonal damage.
authors.affiliation: Department of Biomedical Engineering, Georgia Institute of Technology, Atlanta, GA, United States of America.
authors.forename: Baptiste
authors.initials: B
authors.lastname: Coudrillier
authors.affiliation: Structural Biophysics Group, School of Optometry and Vision Sciences, Cardiff University, Cardiff, United Kingdom.
authors.forename: Jacek K
authors.initials: JK
authors.lastname: Pijanka
authors.affiliation: Glaucoma Center of Excellence, Wilmer Ophthalmological Institute, Johns Hopkins University School of Medicine, Baltimore, MD, United States of America.
authors.forename: Joan L
authors.initials: JL
authors.lastname: Jefferys
authors.affiliation: Department of Mechanical Engineering, Johns Hopkins University, Baltimore, MD, United States of America.
authors.forename: Adhiraj
authors.initials: A
authors.lastname: Goel
authors.affiliation: Glaucoma Center of Excellence, Wilmer Ophthalmological Institute, Johns Hopkins University School of Medicine, Baltimore, MD, United States of America.
authors.forename: Harry A
authors.initials: HA
authors.lastname: Quigley
authors.affiliation: Structural Biophysics Group, School of Optometry and Vision Sciences, Cardiff University, Cardiff, United Kingdom.
authors.forename: Craig
authors.initials: C
authors.lastname: Boote
authors.affiliation: Department of Mechanical Engineering, Johns Hopkins University, Baltimore, MD, United States of America.
authors.forename: Thao D
authors.initials: TD
authors.lastname: Nguyen
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D000465:Algorithms; D001696:Biomechanical Phenomena; D024022:Fibrillar Collagens / Q000737:chemistry / Q000378:metabolism*; D020342:Finite Element Analysis; D005901:Glaucoma / Q000175:diagnosis / Q000378:metabolism / Q000503:physiopathology*; D006801:Humans; D007429:Intraocular Pressure; D016014:Linear Models; D009900:Optic Nerve / Q000473:pathology / Q000503:physiopathology*; D012542:Scattering, Radiation; D012590:Sclera / Q000378:metabolism / Q000473:pathology / Q000503:physiopathology*; D017356:Synchrotrons; D014961:X-Ray Diffraction
chemical_list: D024022:Fibrillar Collagens