title: Assessment of corneal biomechanical properties and their variation with age.
abstract: OBJECTIVE
  The aim of this study was to determine the stress-strain behavior of corneal tissue and how the behavior was affected by age.
  
  
  METHODS
  Human corneal specimens ranging in age between 50 and 95 years were tested under inflation conditions to determine their stress-strain behavior. The corneas were subjected to two load rates that represent dynamic and static loading conditions. The pressure-deformation results were analyzed using shell theory to derive the stress-strain behavior.
  
  
  RESULTS
  The corneas demonstrated clear nonlinear behavior with an initial low stiffness stage and a final high stiffness stage. The transition between the two stages coincided with intraocular pressures between 12 and 20 mmHg. There was a considerable increase in stiffness associated with both age and load rate. Equations were derived to describe the nonlinear stress-strain relationship of corneal tissue for any age between 50 and 95 years, and these equations are presented in a form suitable for use in numerical simulations.
  
  
  CONCLUSIONS
  The cornea demonstrates considerable stiffening with age with the behavior closely fitting an exponential power function typical of collagenous tissue. The increase in stiffness could be related to the additional age-related nonenzymatic cross-linking affecting the stromal collagen fibrils.
authors: Division of Civil Engineering, University of Dundee. Dundee, UK. a.i.h.elsheikh@dundee.ac.uk
authors: Ahmed
authors: A
authors: Elsheikh
authors: Defu
authors: D
authors: Wang
authors: Michael
authors: M
authors: Brown
authors: Paolo
authors: P
authors: Rama
authors: Marino
authors: M
authors: Campanelli
authors: David
authors: D
authors: Pye
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D000375:Aging / Q000502:physiology*; D001696:Biomechanical Phenomena; D003315:Cornea / Q000502:physiology*; D006801:Humans; D008433:Mathematics; D008875:Middle Aged; D013314:Stress, Mechanical