September 2016
Volume 57, Issue 12
Open Access
ARVO Annual Meeting Abstract  |   September 2016
A New Stiffness Parameter in Air Puff Induced Corneal Deformation Analysis
Author Affiliations & Notes
  • Cynthia J Roberts
    Ophthalmology & VIsual Science; and Biomedical Engineering, The Ohio State University, Columbus, Ohio, United States
  • Ashraf M Mahmoud
    Ophthalmology & VIsual Science; and Biomedical Engineering, The Ohio State University, Columbus, Ohio, United States
  • Jeffrey Bons
    Mechanical & Aerospace Engineering, The Ohio State University, Columbus, Ohio, United States
  • Arif Hossain
    Mechanical & Aerospace Engineering, The Ohio State University, Columbus, Ohio, United States
  • Ahmed Elsheikh
    School of Engineering, University of Liverpool , Liverpool, United Kingdom
  • Riccardo Vinciguerra
    Division of Ophthalmology, University of Insubria, Varese, Italy
  • paolo vinciguerra
    Eye Center, Humanitas Clinical and Research Center, Rozzano , Italy
    Vincieye Clinic, Milano, Italy
  • Renato Ambrosio
    Rio de Janeiro Corneal Tomography and Biomechanics Study Group, Rio de Janeiro, Brazil
    Ophthalmology, Federal University of São Paulo , Rio de Janeiro, Brazil
  • Footnotes
    Commercial Relationships   Cynthia Roberts, Oculus (C), Oculus (F); Ashraf Mahmoud, None; Jeffrey Bons, None; Arif Hossain, None; Ahmed Elsheikh, Oculus (F); Riccardo Vinciguerra, None; paolo vinciguerra, Oculus (C); Renato Ambrosio, Oculus (C)
  • Footnotes
    Support  OCULUS Optikgeräte GmbH
Investigative Ophthalmology & Visual Science September 2016, Vol.57, 2390. doi:
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    • Get Citation

      Cynthia J Roberts, Ashraf M Mahmoud, Jeffrey Bons, Arif Hossain, Ahmed Elsheikh, Riccardo Vinciguerra, paolo vinciguerra, Renato Ambrosio; A New Stiffness Parameter in Air Puff Induced Corneal Deformation Analysis. Invest. Ophthalmol. Vis. Sci. 2016;57(12):2390.

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Abstract

Purpose : To investigate a new stiffness parameter in corneal deformation analysis and compare responses in normal (NL) and keratoconic (KC) subjects, matched for intraocular pressure (IOP).

Methods : A new stiffness parameter (SP) is defined as the resultant pressure at inward applanation, divided by corneal deflection amplitude at highest concavity (HCDeflectAmp). The spatial and temporal profiles of the Corvis ST air puff (Oculus, Wetzlar, Germany) were characterized using hot wire anemometry from 0 to 16mm from the nozzle. Measured velocity was correlated with the pressure profile exported by the Corvis ST, measured within the nozzle. The z position of the cornea at the time of inward applanation was used to calculate an adjusted air pressure value (adjAP1) at the time and position of first applanation. An algorithm to correct IOP estimation based on finite element modeling, termed IOPfem, was used for the equation: SP = (adjAP1 - IOPfem)/ HCDeflectAmp. Linear regression analyses between corneal deformation parameters (CDP’s) and SP were performed on a retrospective dataset of 258 KC eyes and 460 NL eyes. CDP’s from a subset of 119 eyes of 119 subjects in each group were matched for IOPfem and compared using t-tests. Significance threshold was p < 0.05.

Results : All CDP’s evaluated showed a significant difference between NL and KC, except peak distance. (Table 1) The KC group had lower SP values, thinner pachymetry, shorter applanation lengths, greater absolute values of applanation velocities, earlier first applanation times and later second applanation times, greater HC deformation and HC deflection amplitudes, and lower HC radius of concave curvature (greater concave curvature). All CDP’s evaluated showed a significant relationship with SP in both groups. Stiffer eyes were associated with greater pachymetry, longer applanation lengths, lower absolute value of applanation velocities, later first applanation times, earlier second applanation times, lower HC deformation and HC deflection amplitudes, shorter peak distances, greater HC radius of concave curvatures (flatter), and higher values of IOPfem.

Conclusions : Keratoconic eyes demonstrated less resistance to deformation than normal eyes with similar IOP. All of the deformation parameters investigated showed a significant relationship with the new stiffness parameter. This may be useful in future biomechanical studies comparing populations without having to match IOP.

This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.

 

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