title: Assessment of corneal biomechanical parameters in myopes and emmetropes using the Corvis ST.
abstract: BACKGROUND
  Prior studies have demonstrated conflicting results regarding the relationship between corneal biomechanical properties and refractive error. Thus, the purpose of this study was to compare the corneal biomechanical parameters of myopes and emmetropes.
  
  
  METHODS
  Ninety-four subjects with varying degrees of myopia (aged 29 to 74 years, spherical equivalent [SE] -0.5 to -17.5 D) and 25 emmetropes (aged 19 to 75 years, SE: -0.5 to +0.5 D) presenting at the Queen Mary Hospital, Hong Kong were recruited sequentially for this prospective study. All patients were phakic with no history of coexisting ocular disease. The corneal biomechanical parameters of the right eye of each subject were analysed using the Corvis ST non-contact tonometer. Intraocular pressure (IOP) was measured using both the Corvis ST and the Topcon Non-Contact Tonometer CT-80. Refractive error was measured by non-cycloplegic subjective and objective refractometry.
  
  
  RESULTS
  High myopes (SE greater than -6.00 D) demonstrated greater mean outward applanation velocities (p < 0.001) and peak distance measurements (p = 0.009) compared to both low to moderate myopes (SE -0.50 to -6.00 D) and emmetropes. Both outward applanation velocity and peak distance were moderately correlated with refractive error (p ≤ 0.001), strongly correlated with IOP and weakly correlated with central corneal thickness. There were no statistically significant differences in age, IOP or central corneal thickness among emmetropes, low to moderate myopes or high myopes.
  
  
  CONCLUSIONS
  Within this study of Chinese subjects, high myopes demonstrate greater corneal mean outward applanation velocity on Corvis ST testing, than emmetropes. In particular, those with high myopia (SE greater than -6.00 D) show a distinct corneal biomechanical profile relative to those with either emmetropia or low to moderate myopia using the Corvis ST.
authors.affiliation: Stanford University School of Medicine, Palo Alto, California, USA. rhlee@stanford.edu.
authors.forename: Rachel
authors.initials: R
authors.lastname: Lee
authors.affiliation: Stanford University School of Medicine, Palo Alto, California, USA.
authors.forename: Robert T
authors.initials: RT
authors.lastname: Chang
authors.affiliation: The Department of Ophthalmology, The University of Hong Kong Faculty of Medicine, Hong Kong, China.
authors.forename: Ian Y H
authors.initials: IY
authors.lastname: Wong
authors.affiliation: The Department of Ophthalmology, The University of Hong Kong Faculty of Medicine, Hong Kong, China.
authors.forename: Jimmy S M
authors.initials: JS
authors.lastname: Lai
authors.affiliation: The Department of Ophthalmology, The University of Hong Kong Faculty of Medicine, Hong Kong, China.
authors.forename: Jacky W Y
authors.initials: JW
authors.lastname: Lee
authors.affiliation: Stanford University School of Medicine, Palo Alto, California, USA.
authors.forename: Kuldev
authors.initials: K
authors.lastname: Singh
mesh_terms: D000328:Adult; D000368:Aged; D001696:Biomechanical Phenomena; D003315:Cornea / Q000503:physiopathology*; D063171:Corneal Pachymetry; D004548:Elasticity; D058453:Emmetropia / Q000502:physiology*; D005260:Female; D006801:Humans; D007429:Intraocular Pressure / Q000502:physiology; D008297:Male; D008875:Middle Aged; D009216:Myopia / Q000503:physiopathology*; D011446:Prospective Studies; D014065:Tonometry, Ocular; D014792:Visual Acuity; D055815:Young Adult
keywords: Corvis ST; IOP; central corneal thickness; corneal biomechanics; emmetropia; myopia