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

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.