title: High myopes have lower normalised corneal tangent moduli (less 'stiff' corneas) than low myopes.
abstract: To compare corneal tangent moduli between low and high myopes.
  
  
  
  Corneal hysteresis (CH) and corneal resistance factor (CRF) of 32 low and 32 high myopes were obtained using an Ocular Response Analyzer, followed by a corneal indentation device that measured corneal stiffness. Corneal topography, pachymetry, Goldmann applanation tonometry intraocular pressure (GAT-IOP), and corneal compensated intraocular pressure (IOPcc) were also obtained. Corneal tangent modulus was calculated on the basis of corneal stiffness, central corneal thickness and corneal radius. Comparisons between groups and associations between corneal biomechanical and ocular parameters were performed.
  
  
  
  Corneal tangent moduli were positively correlated with GAT-IOP (R2= 0.078, p = 0.025), and IOPcc (R2= 0.12, p = 0.006). Despite similarity in corneal thickness and radius, high myopes exhibited a significantly higher IOPcc (16.4 ± 2.51 mmHg) than low myopes (13.1 ± 1.96 mmHg; t(62) = -5.57, p < 0.0001). Both groups had similar corneal stiffness (0.063 ± 0.0085 and 0.063 ± 0.0079 N mm-1for low and high myopes, respectively) and CRF (9.6 ± 1.58 and 9.5 ± 1.90 mmHg for low and high myopes, respectively). Moreover, high myopes exhibited a significantly lower CH (9.5 ± 1.51 mmHg) than low myopes (10.6 ± 1.38 mmHg; t(62) = 2.92, p = 0.005). After normalising corneal tangent moduli to the mean intraocular pressure in normal eyes (15.5 mmHg) using IOPcc, high myopes showed a significantly lower corneal tangent moduli (0.47 ± 0.087 MPa) than low myopes (0.57 ± 0.099 MPa; t(62) = 4.17, p < 0.0001).
  
  
  
  High myopes had lower normalised corneal tangent moduli than low myopes, which indicated that their corneas were less stiff. This is the first in vivo study comparing elastic moduli of the cornea in different refractive groups. Further studies are warranted to understand whether a less stiff cornea is a cause for or an outcome from myopia development.
authors.affiliation: School of Optometry, Hong Kong Polytechnic University, Hong Kong, Hong Kong.
authors.forename: Ying
authors.initials: Y
authors.lastname: Hon
authors.affiliation: Department of Mechanical and Aerospace Engineering, Hong Kong University of Science and Technology, Hong Kong.
authors.forename: Guo-Zhen
authors.initials: GZ
authors.lastname: Chen
authors.affiliation: Department of Mechanical and Aerospace Engineering, Hong Kong University of Science and Technology, Hong Kong.
authors.forename: Shu-Hao
authors.initials: SH
authors.lastname: Lu
authors.affiliation: Department of Mechanical and Aerospace Engineering, Hong Kong University of Science and Technology, Hong Kong.
authors.forename: David C C
authors.initials: DC
authors.lastname: Lam
authors.affiliation: School of Optometry, Hong Kong Polytechnic University, Hong Kong, Hong Kong.
authors.forename: Andrew K C
authors.initials: AK
authors.lastname: Lam
mesh_terms: D000328:Adult; D058452:Axial Length, Eye / Q000503:physiopathology*; D003315:Cornea / Q000473:pathology / Q000503:physiopathology*; D019781:Corneal Topography; D004548:Elasticity; D005260:Female; D006801:Humans; D007429:Intraocular Pressure; D008297:Male; D047728:Myopia, Degenerative / Q000175:diagnosis / Q000503:physiopathology*; D012720:Severity of Illness Index; D055815:Young Adult
keywords: corneal biomechanics; corneal indentation; elastic modulus; stiffness