Akram Abdelazim Joda1,2, Mir Mohi Sefat Shervin3, Daniel Kook4, Ahmed Elsheikh1,5. 1. a School of Engineering , University of Liverpool , Liverpool , UK. 2. b Department of Mechanical Engineering , College of Engineering, King Faisal University , Al-Ahsa , Kingdom of Saudi Arabia. 3. c Smile Eyes Clinic , Munich , Germany. 4. d Department of Ophthalmology , Ludwig-Maximilians-University , Munich , Germany. 5. e NIHR Biomedical Research Centre for Ophthalmology , Moorfields Eye Hospital NHS Foundation Trust and UCL Institute of Ophthalmology , London , UK.
Abstract
PRIMARY 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. MATERIALS AND 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.
PRIMARY 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. MATERIALS AND 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.