title: In vivo study of corneal responses to increased intraocular pressure loading.
abstract: BACKGROUND
  The cornea is responsible for two-thirds of the eye's refractive power which is a function of the shape and refractive index. The aim of this present study is to examine human eyes in vivo for corneal shape changes in response to short-term elevation in intraocular pressure.
  
  
  METHODS
  Videokeratographic and tonometric assessments at baseline were compared with the same assessments when intraocular pressure was elevated to approximately double (199 ± 22 %) the baseline levels using ophthalmodynamometer applanation of the sclera. Composite maps of the cornea and limbus were created by combining topographical assessments for central, nasal, temporal, inferior and superior fixation. Numerical finite-element simulations were custom built for each subject and the stiffness distribution across corneal surface modified to achieve matches between simulated and experimental data.
  
  
  RESULTS
  The stiffness distributions required to achieve simulation-experimental matches showed a consistent trend with the 2.5 mm annulus bounded by the limbus showing a mean stiffness reduction of 47.3 ± 10.8 % compared with the central cornea (P = 0.001).
  
  
  CONCLUSIONS
  Corneal structure appears to provide the central cornea with a greater stiffness compared with the peripheral cornea and associated greater tolerance to elevation in intraocular pressure, consistent with the need for stable corneal refraction and vision. The method adopted to examine corneal biomechanical performance in vivo may have applications in additional studies.
authors.affiliation: School of Engineering, University of Liverpool, Brownlow Hill, Liverpool, L69 3GH UK ; National Institute for Health Research (NIHR) Biomedical Research Centre, Moorfields Eye Hospital NHS Foundation Trust and UCL Institute of Ophthalmology, London, UK.
authors.forename: Ahmed
authors.initials: A
authors.lastname: Elsheikh
authors.affiliation: School of Optometry and Vision Science, University of New South Wales, Sydney, Australia.
authors.forename: Charles W
authors.initials: CW
authors.lastname: McMonnies
authors.affiliation: School of Engineering, University of Liverpool, Brownlow Hill, Liverpool, L69 3GH UK.
authors.forename: Charles
authors.initials: C
authors.lastname: Whitford
authors.affiliation: School of Optometry and Vision Science, University of New South Wales, Sydney, Australia.
authors.forename: Gavin C
authors.initials: GC
authors.lastname: Boneham
keywords: Corneal biomechanics; Numerical simulation; Topography