title: Variability of Corneal Deformation Response in Normal and Keratoconic Eyes.
abstract: OBJECTIVE
  To compare the corneal deformation response, central corneal thickness (CCT), and intraocular pressure (IOP) measurements and their test-retest variability obtained with an ultrahigh-speed Scheimpflug camera between normal and keratoconus eyes.
  
  
  METHODS
  Three consecutive measurements were obtained using Corvis ST. The following parameters were analyzed: A1 and A2 length (length of flattened cornea at first and second applanation), A1 and A2 velocity (deformation velocity until first and second applanation), corneal deformation amplitude (deformation amplitude of cornea at the highest concavity), peak distance (distance of two apices of cornea at time of highest concavity), and radius of corneal curvature at the time of maximum deformation. Repeatability coefficient and intraclass correlation coefficient were measured. Linear mix models were used to adjust for the effect of age, CCT, and IOP on corneal deformation response parameters.
  
  
  RESULTS
  Twelve normal subjects and 12 keratoconus patients were included. Data from only one eye of each participant were randomly selected for analysis. Significant differences were found in corneal deformation amplitude (p < 0.001) and radius of corneal curvature (p < 0.001) between normal and keratoconus eyes after adjusting for age, CCT, and IOP. Although there was no significant difference of intraclass correlation coefficient between the groups, repeatability coefficient values of A1 and A2 length, A1 velocity, and peak distance were significantly smaller in normal eyes as compared with keratoconus eyes (p ≤ 0.023).
  
  
  CONCLUSIONS
  Corvis ST showed adequate repeatability for measurement of corneal deformation amplitude, CCT, and IOP in normal and keratoconus eyes. It may be used to understand ocular pathologies associated with altered biomechanical properties.
authors.affiliation: *PhD †BSc ‡MD, FRCOphth Department of Ophthalmology and Visual Sciences, The Chinese University of Hong Kong, Hong Kong (all authors); Department of Mathematics and Statistics, Hang Seng Management College, Hong Kong (MY); and Centre for Eye Research Australia, University of Melbourne, Victoria, Australia (VJ).
authors.forename: Cong
authors.initials: C
authors.lastname: Ye
authors.forename: Marco
authors.initials: M
authors.lastname: Yu
authors.forename: Gilda
authors.initials: G
authors.lastname: Lai
authors.forename: Vishal
authors.initials: V
authors.lastname: Jhanji
mesh_terms: D000328:Adult; D000368:Aged; D003315:Cornea / Q000503:physiopathology*; D063171:Corneal Pachymetry; D019781:Corneal Topography; D004548:Elasticity / Q000502:physiology*; D005260:Female; D006801:Humans; D007429:Intraocular Pressure / Q000502:physiology*; D007640:Keratoconus / Q000503:physiopathology*; D008297:Male; D008875:Middle Aged; D010781:Photography / Q000379:methods; D012029:Refraction, Ocular / Q000502:physiology; D041623:Tomography, Optical Coherence; D014065:Tonometry, Ocular; D014792:Visual Acuity / Q000502:physiology