title: Repeatability of a novel corneal indentation device for corneal biomechanical measurement.
abstract: OBJECTIVE
  The aim of the study was to evaluate the repeatability of a new device for measuring corneal biomechanics.
  
  
  METHODS
  Twenty-nine normal subjects aged 20-28 years (23.4 ± 1.7 years) underwent measurements of corneal stiffness and tangent elastic modulus using a novel corneal indentation device. Corneal topography, axial biometry and Goldmann applanation tonometry were also performed during the visit. Subjects returned after about 1 week, at approximately the same time, and with the corneal biomechanics, corneal topography and Goldmann applanation tonometry measured again. Both the intrasession and intersession repeatability was assessed.
  
  
  RESULTS
  Both the corneal stiffness and tangent elastic modulus demonstrated good intrasession repeatability (corneal stiffness: coefficient of variation = 7.32%, intraclass correlation coefficient = 0.75; tangent elastic modulus: coefficient of variation = 7.34%, intraclass correlation coefficient = 0.84). The mean modulus after normalised to normal intraocular pressure of 15.5 mmHg was 0.755 ± 0.159 MPa. There was no significant difference between the two visits (paired t-tests: p > 0.05). The repeatability [1.96 times the standard deviation (S.D.) of the intersession difference] of the corneal stiffness and the tangent elastic modulus was 0.0022 N mm(-1) and 0.197 MPa, respectively.
  
  
  CONCLUSIONS
  The corneal indentation device has good intrasession and intersession repeatability. It has good potential to measure corneal biomechanics clinically, even at different corneal regions.
authors.affiliation: School of Optometry, The Hong Kong Polytechnic University, Hong Kong.
authors.forename: Andrew K C
authors.initials: AK
authors.lastname: Lam
authors.affiliation: School of Optometry, The Hong Kong Polytechnic University, Hong Kong.
authors.forename: Ying
authors.initials: Y
authors.lastname: Hon
authors.affiliation: Department of Mechanical and Aerospace Engineering, The Hong Kong University of Science and Technology, Hong Kong.
authors.forename: Leo K K
authors.initials: LK
authors.lastname: Leung
authors.affiliation: Department of Mechanical and Aerospace Engineering, The Hong Kong University of Science and Technology, Hong Kong.
authors.forename: David C C
authors.initials: DC
authors.lastname: Lam
mesh_terms: D000328:Adult; D003315:Cornea / Q000502:physiology*; D019781:Corneal Topography / Q000295:instrumentation*; D055119:Elastic Modulus / Q000502:physiology; D005260:Female; D006801:Humans; D007429:Intraocular Pressure / Q000502:physiology; D008297:Male; D015203:Reproducibility of Results; D014065:Tonometry, Ocular / Q000295:instrumentation*; D055815:Young Adult
keywords: corneal biomechanics; elastic modulus; intraocular pressure; stiffness