title: Identification of biomechanical properties of the cornea: the ocular response analyzer.
abstract: OBJECTIVE
  Several methods have been devised for measuring geometric parameters of the cornea but, until now, the biomechanics of the cornea have been largely ignored. The relatively new Ocular Response Analyzer (ORA) provides such biomechanical information. In order to correctly interpret the underlying biomechanics of ORA data, we review reported ORA measurements and provide a compendium of factors influencing these measurements, with discussion of possible explanations for ORA measurement results.
  
  
  METHODS
  This review comprised a literature search using "ocular response analyzer" and "ocular response analyser" as keywords. We reviewed and compared reported results from recent ORA studies so obtained, with an eye to understanding corneal biomechanics.
  
  
  RESULTS
  Several ORA biomechanical parameters of the cornea - corneal hysteresis (CH) and corneal resistant factor (CRF) - characterize the viscoelastic properties of the cornea, especially those of the ground substance. The impact on CH and CRF values of various independent factors, e.g. intraocular pressure (IOP), age, central corneal thickness (CCT), and corneal swelling, are discussed. The impact on CH and CRF of treatment-related structural changes of the cornea, i.e. those occurring after refractive surgical procedures, placement of intracorneal rings, and collagen crosslinking (CXL), as well as pathological changes of the cornea, e.g. those resulting from keratoconus, edema, and glaucoma, are discussed.
  
  
  CONCLUSIONS
  Changes in CRF and CH may be reflective of structural changes in the ground substance of the cornea. Thus, ORA provides invaluable information for delineating biomechanical conditions pertaining to the cornea, with special regard to ocular diseases, e.g. keratoconus and glaucoma.
authors.affiliation: Department of Ophthalmology, Carl Gustav Carus University Hospital, Dresden, Germany. naim.terai@uniklinikum-dresden.de
authors.forename: Naim
authors.initials: N
authors.lastname: Terai
authors.forename: Frederik
authors.initials: F
authors.lastname: Raiskup
authors.forename: Michael
authors.initials: M
authors.lastname: Haustein
authors.forename: Lutz E
authors.initials: LE
authors.lastname: Pillunat
authors.forename: Eberhard
authors.initials: E
authors.lastname: Spoerl
mesh_terms: D001696:Biomechanical Phenomena / Q000502:physiology*; D003315:Cornea / Q000033:anatomy & histology / Q000502:physiology*; D003941:Diagnostic Techniques, Ophthalmological / Q000295:instrumentation*; D004548:Elasticity / Q000502:physiology*; D006801:Humans; D007429:Intraocular Pressure / Q000502:physiology; D009929:Organ Size; D054140:Refractive Surgical Procedures; D013666:Tears / Q000737:chemistry