June 2015
Volume 56, Issue 7
Free
ARVO Annual Meeting Abstract  |   June 2015
Clinical Evaluation of Correction Algorithm for Corvis ST Tonometry
Author Affiliations & Notes
  • Ahmed Elsheikh
    School of Engineering, University of Liverpool, Liverpool, United Kingdom
    NIHR Biomedical Research Centre, Moorfields Eye Hospital NHS Foundation Trust, London, United Kingdom
  • Akram Joda
    School of Engineering, University of Liverpool, Liverpool, United Kingdom
  • Riccardo Vinciguerra
    Eye Center, Humanitas Clinical and Research Center, Rozzano, Italy
  • Paolo Vinciguerra
    Eye Center, Humanitas Clinical and Research Center, Rozzano, Italy
  • Daniel Kook
    Center of Refractive Therapy, Ludwig Maximilians University Munich, Munich, Germany
  • Shervin Sefat
    Smile Eyes Private Eye Clinic, Munich, Germany
  • FangJun Bao
    Wenzhou Medical University, Wenzhou, China
  • Footnotes
    Commercial Relationships Ahmed Elsheikh, Oculus (F); Akram Joda, Oculus (F); Riccardo Vinciguerra, None; Paolo Vinciguerra, None; Daniel Kook, None; Shervin Sefat, None; FangJun Bao, None
  • Footnotes
    Support None
Investigative Ophthalmology & Visual Science June 2015, Vol.56, 101. doi:
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      Ahmed Elsheikh, Akram Joda, Riccardo Vinciguerra, Paolo Vinciguerra, Daniel Kook, Shervin Sefat, FangJun Bao; Clinical Evaluation of Correction Algorithm for Corvis ST Tonometry. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):101.

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      © ARVO (1962-2015); The Authors (2016-present)

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Abstract
 
Purpose
 

To develop and clinically evaluate a correction algorithm to improve the accuracy of intraocular pressure (IOP) measurements made by the non-contact Corvis ST (CVS) tonometer, which considers the combined effects of variations in central corneal thickness (CCT), age and the IOP level itself.

 
Methods
 

Nonlinear numerical simulations based on the finite element method were used to represent corneal behaviour under the effect of IOP and the CVS air pressure. The simulations considered important biomechanical properties including the cornea’s non-uniform thickness, elliptical topography, weak stromal inter-lamellar cohesion, low epithelial and endothelial stiffness, and hyperelastic and hysteretic material behaviour. The simulations represented the CVS procedure on corneas to obtain a correction algorithm based on the values of CCT, age and the measured IOP. The effectiveness of the algorithm in reducing the effects of corneal parameters on CVS-IOP was assessed using three independent clinical databases involving 632, 1047 and 99 participants, respectively and obtained at Smile Eyes Clinics, Germany, Humanitas Clinical and Research Center, Italy and Wenzhou Medical University, China.

 
Results
 

CCT was the dominant stiffness factor affecting CVS-IOP, and both CCT and age had a nonlinear (second order) effect on the IOP measurements. The correction algorithm was successful in significantly reducing the strength of association between CVS-IOP and CCT in the three clinical databases respectively, from 0.031 mmHg/um (R2=0.204) to 0.004 mmHg/um (R2=0.004), from 0.029 mmHg/um (R2=0.095) to 0.009 mmHg/um (R2=0.016) and from 0.033 mmHg/um (R2=0.222) to 0.001 mmHg/um (R2=00), Figs. 1 and 2. The association with age was weak, remaining below 0.06 mmHg/year (R2=0.05) in all three databases and reducing slightly with the correction algorithm.

 
Conclusions
 

The CVS correction algorithm considerably reduced the dependence of CVS-IOP on CCT, addressing an important error source in CVS-IOP measurements. The consistency in performance of the new algorithm over three independent clinical databases indicates the suitability of the algorithm for clinical utility.  

 
Fig 1 Effectiveness of algorithm in reducing association of CVS-IOP with CCT for a clinical database with 632 participants
 
Fig 1 Effectiveness of algorithm in reducing association of CVS-IOP with CCT for a clinical database with 632 participants
 
 
Fig 2 Effectiveness of algorithm in reducing association of CVS-IOP with CCT for a clinical database with 1047 participants
 
Fig 2 Effectiveness of algorithm in reducing association of CVS-IOP with CCT for a clinical database with 1047 participants

 
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