title: Development and validation of a correction equation for Corvis tonometry.
abstract: OBJECTIVE
  This study uses numerical analysis and validation against clinical data to develop a method to correct intraocular pressure (IOP) measurements obtained using the Corvis Tonometer for the effects of central corneal thickness (CCT), and age.
  
  
  METHODS
  Finite element analysis was conducted to simulate the effect of tonometric air pressure on the intact eye globe. The analyses considered eyes with wide variations in IOP (10-30 mm Hg), CCT (445-645 microns), R (7.2-8.4 mm), shape factor, P (0.6-1) and age (30-90 years). In each case, corneal deformation was predicted and used to estimate the IOP measurement by Corvis (CVS-IOP). Analysis of the results led to an algorithm relating estimates of true IOP as a function of CVS-IOP, CCT and age. All other parameters had negligible effect on CVS-IOP and have therefore been omitted from the algorithm. Predictions of corrected CVS-IOP, as obtained by applying the algorithm to a clinical data-set involving 634 eyes, were assessed for their association with the cornea stiffness parameters; CCT and age.
  
  
  RESULTS
  Analysis of CVS-IOP measurements within the 634-large clinical data-set showed strong correlation with CCT (3.06 mm Hg/100 microns, r(2) = 0.204) and weaker correlation with age (0.24 mm Hg/decade, r(2) = 0.009). Applying the algorithm to IOP measurements resulted in IOP estimations that became less correlated with both CCT (0.04 mm Hg/100 microns, r(2) = 0.005) and age (0.09 mm Hg/decade, r(2) = 0.002).
  
  
  CONCLUSIONS
  The IOP correction process developed in this study was successful in reducing reliance of IOP measurements on both corneal thickness and age in a healthy European population.
authors.affiliation: a School of Engineering , University of Liverpool , Liverpool , UK.|b Department of Mechanical Engineering , College of Engineering, King Faisal University , Al-Ahsa , Kingdom of Saudi Arabia.
authors.forename: Akram Abdelazim
authors.initials: AA
authors.lastname: Joda
authors.affiliation: c Smile Eyes Clinic , Munich , Germany.
authors.forename: Mir Mohi Sefat
authors.initials: MM
authors.lastname: Shervin
authors.affiliation: d Department of Ophthalmology , Ludwig-Maximilians-University , Munich , Germany.
authors.forename: Daniel
authors.initials: D
authors.lastname: Kook
authors.affiliation: a School of Engineering , University of Liverpool , Liverpool , UK.|e NIHR Biomedical Research Centre for Ophthalmology , Moorfields Eye Hospital NHS Foundation Trust and UCL Institute of Ophthalmology , London , UK.
authors.forename: Ahmed
authors.initials: A
authors.lastname: Elsheikh
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000465:Algorithms; D003315:Cornea / Q000033:anatomy & histology; D063171:Corneal Pachymetry; D006801:Humans; D007429:Intraocular Pressure; D008875:Middle Aged; D008962:Models, Theoretical; D009716:Numerical Analysis, Computer-Assisted; D011312:Pressure; D015203:Reproducibility of Results; D013997:Time Factors; D014065:Tonometry, Ocular / Q000379:methods*; D055815:Young Adult
keywords: Corvis ST; Tonometry; cornea; intraocular pressure; ocular biomechanics