A Comparison of Three Techniques for Measurement of Intraocular Pressure in Normal Eyes

Abstract

Objectives: To compare the precision of intraocular pressure (IOP) measurements acquired using an ocular response analyser (ORA), Auto Kerato-Refracto-Tonometer (TRK-1P), and Goldmann applanation tonometer (GAT) in healthy eyes. Methods:In this prospective study, one eye of each of 57 normal subjects was randomly selected for analysis. Measurements of the IOP were performed using ORA, TRK-1P, and GAT, and measurements of corneal hysteresis (CH), corneal resistance factor (CRF), and central corneal thickness (CCT) were performed using ORA. Repeatability was assessed by the coefficient of variation (CV) and interclass correlation coefficients (ICCs). Agreement among tonometers was assessed by Bland-Altman plots and one-way ANOVA. Results:The average IOPs measured using Goldmann-correlated IOP (IOPg), corneal-compensated IOP (IOPcc), TRK-1P, and GAT (± SDs) were 15.13 ± 2.76, 14.39 ± 2.59, 16.54 ± 2.93, and 15.21 ± 2.54 mmHg, respectively. Intra-observer agreement across all tonometers was strong and slightly higher for GAT and IOPg than for TRK-1P. The intra-observer CVs for GAT IOPg, and TRK-1P, were 4.22 (ICC=0.94), 4.99 (ICC=0.93), and 6.69 (ICC=0.86), respectively. Inter-observer agreement between various measurement methods was evaluated with Bland-Altman plots with multiple measurements per subject and ICCs. Results indicated fairly poor agreement across measurement methods, as supported by large limits of agreement and ICCs. Conclusion:GAT, ORA, and TRK-1P are highly reliable methods for measurement of the IOP; however, the instruments cannot be used interchangeably.