title: Assessment of the biomechanical properties of the cornea with the ocular response analyzer in normal and keratoconic eyes.
abstract: OBJECTIVE
  To compare hysteresis, a novel measure of ocular rigidity (viscoelasticity) in normal and keratoconic eyes.
  
  
  METHODS
  The study consisted of 207 normal and 93 keratoconic eyes. Eyes were diagnosed as keratoconic based on clinical examination and corneal topography. The hysteresis was measured by the Ocular Response Analyzer (ORA; Reichert Ophthalmic Instruments, Buffalo, NY). The data were recorded by Generation 3 software for the ORA. Central corneal thickness (CCT) was measured with a handheld ultrasonic pachymeter in the midpupillary axis.
  
  
  RESULTS
  The mean hysteresis was 10.7 +/- 2.0 (SD) mm Hg (range, 6.1-17.6) in normal eyes compared with 9.6 +/- 2.2 mm Hg (range, 4.7-16.7) in keratoconic eyes. The difference was statistically significant (P < 0.0001, unpaired t-test). Mean CCT in the normal and keratoconic eyes was 545.0 +/- 36.4 microm (range, 471-650) and 491.8 +/- 54.7 microm (range, 341-611), respectively; the difference was significant (P < 0.0001, unpaired t-test).
  
  
  CONCLUSIONS
  Hysteresis was significantly higher in normal than in keratoconic eyes. It may be a useful measurement in addition to CCT, when assessing ocular rigidity, and may be of particular importance when trying to correct intraocular measurements for increased or decreased ocular rigidity. Long-term studies of change in hysteresis may provide information on the progression of keratoconus.
authors.affiliation: Birmingham Heartlands and Solihull NHS Trust, Solihull, United Kingdom. sunilshah@doctors.net.uk
authors.forename: Sunil
authors.initials: S
authors.lastname: Shah
authors.forename: Mohammed
authors.initials: M
authors.lastname: Laiquzzaman
authors.forename: Rajan
authors.initials: R
authors.lastname: Bhojwani
authors.forename: Sanjay
authors.initials: S
authors.lastname: Mantry
authors.forename: Ian
authors.initials: I
authors.lastname: Cunliffe
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D003315:Cornea / Q000000981:diagnostic imaging / Q000503:physiopathology*; D019781:Corneal Topography; D003941:Diagnostic Techniques, Ophthalmological; D004548:Elasticity; D005260:Female; D006801:Humans; D007640:Keratoconus / Q000503:physiopathology*; D008297:Male; D008875:Middle Aged; D014463:Ultrasonography