Comparison of Intraocular Pressure Using Goldmann's Applanation Tonometer as the ‎Current‏ ‏Standard of Clinics with Five Different Tonometers in Healthy People

Abstract

Purpose:To compare the intraocular pressure (IOP) measured with the Goldmann tonometer as the current standard of clinics with five different tonometers in healthy people, and to investigate the effect of corneal thickness and biomechanical properties on measurements.Methods:In this cross-sectional study, IOP was measured in 94 eyes of 94 healthy subjects with the Goldmann, manual applanation resonance, Icare, Topcon non-contact, Ocular Response Analyzer and Corvis’s tonometers. Comparison of the IOPs measured with different techniques was done using the repeated measures analysis of variance while the central corneal thickness as a covariate. The Bland-Altman plots and intraclass correlation coefficients were used to assess the agreement between the measurements. Limits of agreement were determined as the mean difference ±1.96 SD. Regression analysis was used to estimate the effect of central corneal thickness, corneal hysteresis, and corneal resistance factor on IOPs obtained using different tonometers.Results:The lowest mean IOP was obtained with the Goldmann tonometer (13.1 ± 2.6 mmHg) and the highest with the Topcon non-contact tonometer (17.3 ± 2.5 mm Hg). There was a statistically significant difference between the pressure measured by Goldmann's tonometer and other tonometers. The mean IOP measured using Icare (14.6 ± 3.4 mmHg) demonstrated the smallest mean difference and the highest agreement with the Goldmannn tonometer results. Central corneal thickness significantly affected all IOPs except the cornea-compensated IOP (IOPcc). The highest influence of IOP on the corneal resistance factor was related to Topcon non-contact tonometer and Goldmann correlated IOP (IOPg), while the lowest was seen with IOPcc and Goldmann.Conclusions:The Icare tonometer had the highest agreement among the different tonometers with the Goldmann tonometer. The central thickness of the cornea affects the results of all tonometers except IOPcc. Among the two evaluated corneal biomechanical parameters, the corneal resistance factor was the only biomechanical parameter effective on IOPs measured with all devices.

Keywords

• tonometry
• intraocular pressure
• corneal thickness
• corneal hysteresis
• corneal resistance factor