Comparison between rebound tonometer and Tono-Pen® in relation to Goldmann applanation tonometry and the influence of central corneal thickness on these three methods

Abstract

Objective: to compare intraocular pressure (IOP) measurements from two different instruments, the rebound tonometer (Icare®) and the Tono-Pen® XL (TP), with that from Goldmann applanation tonometer (GAT) and to determine the influence of central corneal thickness on these three instruments. Methods: 274 eyes from 137 healthy volunteers were evaluated in this cross-sectional study. All IOP measurements were made by the same examiner who was blinded to the observed result. Icare® tonometry was performed first, followed by TP, GAT, and pachymetry in a random order. Results: a good correlation was observed between IOP measurements obtained with Icare® and GAT (r = 0.79, p = 0.000) and between TP and GAT (r = 0.69, p = 0.000). Icare® and TP measurements were consistently higher than GAT measurements. A Bland-Altman plot indicated that the 95% limits of agreement between Icare® and GAT were 0.98 ± 3.12 (mean ± SD; range, -5.14 to 7.11) mmHg, and those between TP and GAT were 1.88 ± 3.20 (range, -4.38 to 8.15) mmHg. In the group of patients with thinner corneas, Icare® overestimated IOP by 0.5mmHg compared with IOP obtained using GAT and by 1.8 mmHg compared with IOP obtained using TP. In the group of patients with thicker corneas, Icare® overestimated IOP by 1.4 mmHg compared IOP obtained using GAT and by 1.5 mmHg compared with IOP obtained using TP. Conclusion: IOP measurements obtained with Icare® and TP showed a good correlation with that of GAT. Both tonometers tend to overestimate IOP compared to GAT. In patients with thinner corneas, Icare® perfrmed better than TP.