Can Corneal Biomechanical Properties Explain Difference in Tonometric Measurement in Normal Eyes?

Corneal biomechanical parameters can affect intraocular pressure (IOP) measurements by different tonometers compared with Goldmann applanation tonometer. This study implies that corneal hysteresis (CH) and corneal resistance factor (CRF) better explain variability in IOP measurements.

The aim of this study was to evaluate the effect of corneal properties on the difference in IOP measured by the Ocular Response Analyzer (ORA), Rebound Tonometer (RBT), Dynamic Contour Tonometer (DCT), and Tono-Pen from the Goldmann applanation tonometer (GAT).

An observational study was done on healthy participants in a tertiary eye care center. Corneal curvature was measured with a manual keratometer prior to IOP measurements. Intraocular pressure was measured by a single trained examiner with ORA, RBT, DCT, GAT, and Tono-Pen. CH and CRF were measured using the ORA. Central corneal thickness was measured using the ultrasonic pachymeter. Only the right eye was included for analysis. One-way analysis of variance was performed to compare variables, Bland-Altman plots to assess agreement, and regression analyses to study associated factors.

We included 82 eyes of 82 participants with a mean age of 40.9 (14.3) years. Mean ± SD DCT IOP (15.22 ± 1.98) mmHg was significantly higher than GAT IOP (13.73 ± 2.42) (P = .01) and ORA Goldmann correlated IOP (13.66 ± 3.16) (P = .003). The limits of agreement between GAT and other tonometers measurements ranged between -5.0 and 2.1 mmHg. With multiple linear regression analyses, CH and CRF were found to be associated with the measured IOP differences between GAT and ORA (corneal compensated IOP and Goldmann correlated IOP) (P < .001) and DCT (P = .014, <.001) whereas differences between GAT and RBT measurements were independently explained by corneal curvature (P = .035) and central corneal thickness (P = .045).

There was good agreement between GAT and other tonometers, but was not good enough for them to be used interchangeably. A combination of CH and CRF may better explain the variability between GAT and tonometers.