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.

International comparisons of intraocular pressures, as measured by Tono-Pen and Goldmann applanation tonometry, in healthy adults: A meta-analysis

“…Over time, investigators have reported comparison studies in which TP reveal IOP greater than, equal to, and less than IOPs measured by the current gold standard GAT. [3–28]…”

“…This variability and inconsistencies in reported studies have resulted in a confused professional literature. The variability has been explained by differences in research study designs, [3] research methods applied, [4] statistical approaches used to analyze IOP measurements, [5,6] eye biomechanics, [7,8] diurnal variations of IOP, [9] body positions in which measurements were taken (sitting or supine), [10,11] age of subjects, [12–14] ethnicity of subjects, [15] central corneal thickness (CCT), [7,16–21,29] cornea shape, [22] level of training and skill of eye care professional making the measurements (ophthalmologist, technician), [23,24] subjectivity of GAT measurements, [25,26] and fundamental principles of physics underlying the differences in how IOP are measured by the TP or GAT procedure. [7,22,27,28,30]…”